aj mccormack and son

Flags & Slabs - Page 10
The Brew Cabin
flags and slabs


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Forum Question Joints turning green - Keith - Sep 14th 2003
I have laid a patio for a good customer. Since last year the some of the Bradstone slabs and many of the pointed joints have turned green. It is not moss but may be a type of fungus. There are deciduous trees nearby but not directly over the paving. There are also two dogs who use the patio regularly. frown

Any ideas as to what may have caused the greening, and how can it be controlled?

forum answer Tony McCormack - Sep 15th 2003
It's probably algae or possibly a lichen. Swilling down the area with Jeyes Fluid or a good weedkiller should get rid of it.

Jeyes Fluid is good for those paved areas frequented by dogs, as it disinfects their waste products, but is less effective at controlling weed growth, so, it may be a case of using a good weedkiller once every six weeks, and the JF once a fortnight for maximum protection from greening and odour.

Forum Question Cleaning internal stone flags - Jan Hurley - Sep 16th 2003
We have just uncovered stone flags in the hall of our 350 year old cottage. They are very dusty and dirty, We used soda crystals and water to try and clean them up but that does not seem to have made much of a difference, please can you give advise on the best way to clean them and what to use make them shiny?
forum answer Tony McCormack - Sep 16th 2003
A power washer is ideal, if you can protect your internal fittings and furnishings, otherwise, it's hot, soapy water, a wire brush and plenty of elbow grease. There are so-called "Patio Cleaners" but many of these are acid-based and less than ideal for indoor use, or use on stone of an unknown nature - if you want to "risk it", then make sure all the windows are flung wide open, anything valuable is well out of the way, and test a small, discreet, out-of-the-way corner first, as the acid can adversely affect some types of stone.

Once you've got them clean, then I'd suggest using an internal stone polish to make them "shiny" - Golvpolish from HG Hagesan seems to be the most popular choice.

Sep 17th 2003
We have polished Yorkstone flags in our hallway, but they are badly worn in places (like where everyone turns at the foot of the stairs). This wear has caused the flags to start to delaminate, and there are now holes up to two inches deep in places. The previous owners appear to have tried filling these with somethings that I suspect has caused further damage. Is there some sort of filler that will match the existing stone, and not damage it further, or am I in line for a very expensive replacement (the flags are around three foot square)?
Tony McCormack
Sep 17th 2003
You could use a high-strength repair concrete, something like Ultracrete from Instarmac or Monoset from me good friend Simeon at Ronacrete. These are fast-setting, extremely tough, fine aggregate concretes that are used in highway applications, so have a proven pedigree. However, their colouring probably won't match that of your stone flooring, and you'll have to decide whether you want a 'patch' or whether it would be a better job to replace the damged stone completely. Remember, if the stone is delaminating now, it will probably continue to do so.
Forum Question Membranes, pointing and road bases - Mark H - Sep 16th 2003
I have a Victorian Semi with front garden containing a small grass area (3m square) surrounded on 3 sides with earth borders with shrubs in. The 4th side is the path to front door.

I've dug around the edge of grass and borders/path and laid in some quality Victorian rope edgings in a bed of concrete and haunched in.

The area enclosed by the rope edging is thus is 3.1 m square (i.e 3 m square for slabs with bit more for pointing room betwen slabs).

Now I want to remove the grass/earth inside the 3.1 square and lay 600mm sq. riven paving slabs - 37mm thick.

Now the questions Tony et all:

  • - after digging out grass/mud do I need to lay any geo-membrane down or weed kill to stop plants rising?
  • - how deep do I excavate the grass/soil to i.e what thickness of bedding material
  • - what bedding material do you suggest
  • - do I need to compact the soil once excavated and do I need to compact the bedding material

The paving area will only be used for putting flower pots on and sitting on (no cars)  smile

Another question is that do you recommend pointing by sweeping in the mortar dry and spraying with atomiser?

Only last time I "wet" pointed it stained the slabs and was well fiddly!

Sorry for such big list.

PS for Tony - I thought the road base, not sub base, carries design weight in roads/pavements?

Best Rgds - Mark

forum answer Tony McCormack - Sep 17th 2003
All the answers to your questions are on the main website. There's a FAQ on whether a membrane is required, and then the Laying Flags page deals with the bedding requirements and laying details. Once you've got the flags laid, there's a lot of advice on Pointing in that particular section. The atomiser idea is a bit of a nonsense and is best avoided.

On your technical point, it can be argued that a road base carries the loading of a road/pavement, but, as much of this website is devoted to lightweight pavements rather than roads and highways, there isn't a lot to be gained by introducing discussion on construction layers that are often omitted in the type of pavements under consideration. Personally, I still believe the sub-base is just as vital in ensuring pavement strength as is the road base. As sub-bases are present in more pavements, it makes more sense (on this website) to devote more attention to sub-bases and leave discussion of road bases to those areas where higher traffic levels are expected.

Mark H
Sep 17th 2003
Roger Tony re FAQ and pavements. Understood over and out ... except....

Re dry pointing..... where does the moisture come from if you lay flags on dry bed?


Tony McCormack
Sep 17th 2003
I don't like dry grouting/pointing, and although there is some discussion of it on the website, it is there for the sake of completeness, not as a recommendation.

However......a dry grouting mix will draw moisture from underlying materials, whether that's the bedding or the sub-grade, as well as from the pavers themselves and even the atmosphere. The big "but" is that there isn't sufficient moisture available to achieve a satisfactory water:cement ratio, and so you end up with a drastically weakened mortar. Fairy Nuff, your flags aren't stained, but the jointing is a waste of time and materials, in my opinion!

When it comes to laying on a SEMI-dry bed, there should be enough free moisture in the bedding sand to initiate hydration of the cement content, and, because we are only looking for a low-strength binding agent rather than a tough, hard "concrete", an ideal w/c ratio is not required. The key point here is that it is not a dry mix on which the flags are laid, but a semi-dry mix - there is some water present, unlike the situation where a dry grout is used.

Sep 19th 2003
Sorry to labour the point Tony.... how do you lay a semi dry bed?

I assume you mix up sand and cement bed with a really low water content?

Or can you just spray the dry bed with fine water sprinkler?

TIA - Mark

Tony McCormack
Sep 20th 2003
There should be sufficient mositure in your grit sand to allow it to be mixed with the cement without needing to add any additional water. However, if your grit sand is particularly dry for some reason, or if you're adding gravel to the recipe, then some water may need to be added, but it should be kept to an absolute minimum. The usual rule of thumb is that, when you squeeze a handful of the mix, it should clump together but no water should escape - ie damp, but not wet.

Sep 21st 2003
Thanks Tony.

After reading your replies I'm going to lay a dry mix and bite the bullet and point with firm wet grout rather than dry grout.


Forum Question Home-made sub-base - Phileas - Sep 21st 2003
I am intending to construct a patio and have a quantity of flint chippings which I would like to incorporate into the sub-base. If I mix these with sand will this form a suitable sub-base material?

I was hoping to use this mix at the bottom and then crushed stone on top.

forum answer Tony McCormack - Sep 26th 2003
Mixing grit sand and flint chipping would make a reasonable sub-base-cum-fill-layer for a patio, as there's no heavy loads involved, but such a concoction wouldn't be suitable for use beneath a driveway or other pavement that was intended to carry vehicular traffic.
Forum Question New Slate Path & Patio with a twist - LV Lishious - Sep 24th 2003
Thank you for this amazingly informative site. From the posts, it appears that the time you invest in it is appreciated by its users a hundred-fold. I've not seen some of my issues directly addressed elsewhere on the site or I wouldn't bother you. This confluence of circumstances, materials and concerns may be uniquely peculiar to me, but I would appreciate your input nonetheless. I hope you can help me.

I am a do-it-yourselfer in the US (Pennsylvania where the frost heaves are great and the humidity worse). My standard methodology is to build it so it'll last 1000 years---guilty of a bit of overkill. I'm also a recycler and frugal. I'd like to use what I have, and, though it may sound like I'm trying to avoid work, I think underkill may be the way to proceed for this particular project.

I'm building a winding path from my gravel driveway to an out-building where I'm putting my office and from the outbuilding to my deck. The full length of the path will be about 210 feet (64 m). I'll build a small patio in front of the outbuilding about 150 sq. ft. (13.94 sq. m.), and I'm going to put two wide steps (slate slabs?) up to the building's doorway from the patio.

I could build the patio and about one-third of the path in the typical way you describe on your site - the earth is easily removed and I could dump tons of gravel into the void and compact it, etc. However, I have two problems. The first is the paving material (see below). The second is that two-thirds of the path is under some old trees. I've double dug big gardens in this area and the roots of the trees show their gratitude by poking through the new surface within two years. The wooded pathway is criss-crossed by huge surface roots I'd rather not remove. I'm wondering if it's not best to put the path on top of the ground surface rather than fighting nature by digging it in. I can always plant and mound earth up to the sides of the path to disguise its appearance and make it a little safer to use. While the path may be gently undulating in spots, for the most part I should be able to install it so you'd barely notice.

I've gotten a great price on what are called "Slate Mill Ends"---basically they're scrap left after the best pieces are cut to specs. The slates are relatively "square" and they range in size from 6 in. x 1 ft. (15 cm x 30.5 cm) to 2 ft x 2 ft (61 cm square). The bigger problem is they are cleaved and rough and vary in thickness---from each other and within the same piece. The bulk of the larger 2 ft square pieces will be used for the patio and range from 3/4 in to 2 in thick (19 to 51 mm). The smaller slates to be used for the path are predominantly 3/4 to 1 in. thick (19 to 26 mm) so they could be bedded fairly evenly. A few years ago I laid a 50 ft slate mill-end path on finely crushed gravel and spent a lot of time trying to get the surface even---since then it's become quite uneven because the sand and gravel washed out. Given this material, I can't use a flat bed and don't want to take the time make uneven pieces appear flat. Not having tried it, I'm guessing that laying the uneven slate in a bed of mortar is the only way to get the surfaces relatively flat.

MATERIALS FOR BASE - Concrete Panels and Used Sidewalk Slabs
My late dad was a contractor and used to salvage things from various jobs. He salvaged some tongue and groove concrete panels which are about 2 in thick (51mm), 22.5 in. wide (57 cm.) and about 8 ft long (2.4 m). These panels may have been designed as a wall panel but I think they'd be satisfactory for my application. They are also narrow but could be doubled up. Two panels would be 46 in (117 cm) wide. When I bought the slate I anticipated a path about 30 in wide (86 cm.) so I'd be short on slate if I doubled up the panels. 46 in is also a bit wide for my proposed traffic (my personal use and people visiting my office). Doing a curve with these pieces will also be very hard. They will be near impossible to cut because they are reinforced with thick reinforcing wire criss-crossed every 3 in.---I'd need a blowtorch. So my walk would have to be somewhat angular and then I'll try to fill in with cinderblocks to create softer lines. Being tongue and groove, these panels should be fairly easy to piece together to create a nice patio.

I also have about 50 ft. (15 m) of old sidewalk which are about 10 in thick (25 cm) . These slabs were lifted out in 4-5 ft sections. I could sink these down in the areas easily excavated and it would be easy to match the different levels. These sidewalks are also about 24 in. wide (61cm.). The concrete panels and the old sidewalk are free but super heavy. Once in place and back strains healed, I suppose the weight is a plus when the ground heaves (freezes and thaws repeatedly).

So even though I could use the typical installation method on about one-third of the path and on the patio, I have these (free) concrete panels and slabs which may save us a lot of work. Do you agree?

My son and I will do the work but we only want to do it once. Given the ground conditions and the materials I have, how should I proceed?


  • -Can I use the concrete panels and old sidewalk slabs as a good base?
  • -Can the concrete panels be placed on top of the ground rather than in-ground in the wooded area, or is this insane as my son suggests?
  • -Given the panels' and slabs' weight, do they need any footers?
  • -Would the panels have to be laid in a sub-base of crushed stone?
  • -Assuming the slate will be laid on top of the panels and slabs, and given the slates' varying thicknesses, should I bed them in concrete and then point with mortar?
  • -Or should I just bed the slate in mortar even if it does get thick in spots? I'd do my best to pick pieces similar in thickness.
  • -What kind of concrete and/or mortar mix would you recommend?

I know this was a long explanation but I've not seen these issues addressed in any of my research. I have printed your sections on laying brick and block on an inflexible base.

Now that the heat of summer is over, I'd like to get started. Winter comes too early these days.

I look forward to your expert advice. Thanks!

forum answer Tony McCormack - Sep 26th 2003
Well, that's a fairly comprehensive posting! I'll try and work my way through each of the issues, but I should warn you that UK/Irish practice differs from that in the continental USA, and it might be worth checking my thoughts with someone on your side of the water.

I'm not sure why you want to use these great big concrete slabs and panels as a 'base'. They will be difficult to handle, and, because of their size, will act as bridges or blocks rather than as a base. The idea of a base layer (or a sub-base) is to evenly spread the imposed loads onto the underlying layers. By using monolithic blocks such as you propose, you are not really spreading the loads, but transferring them directly to the sub-grade. There will be some load transfer, because the paving units are smaller in surface area than the blocks/slabs, but the pavement will behave as a series of unconnected blocks rather than a flexible whole. This, I think, answers your first question.

On your second point, laying these blocks on top of the existing sub-grade rather than excavating to a formation level is possible, but I can't see how it would benefit the final construction. When you've got a flexible sub-base or base layer, then any minor ground movement caused by light frosting or root growth can often be accommodated by the flexible base/sub-base, but, when the base is a monolithic block, any ground movement is directly transmitted to the surface layer.

On to Q3, and the use of footers is wandering further into the realm of major civil engineering work. The idea of using these reclaimed materials is to reduce the amount of labour and materials required, not make even more work! However, if you did decide to use the blocks/slabs, then you probably would need some form of concrete blinding to seat them securely and prevent them rocking or settling over time.

This brings us on to your next point, regarding the need for a sub-base. This project is assuming massive proportions the more you consider it! A sub-base would be ideal, if you were planning to run your 4x4 over the finished pavement, but, as this is supposed to be a pedestrian only footpath, then using a sub-base AND a base layer of reclaimed blocks/slabs is probably going a bit too far.

And so to your final questions, regarding the bedding of the slate. I think they'd be best laid on a full concrete bed. This would vary in thickness from, say, 200mm (8 in.) to (150mm (6 in.) to accommodate the variation in slate thickness, yet provide adequate resistance to frosting. The concrete should be a reasonably strong mix, something around 20-30 Newtons (that's roughly 1 part cement to 2 parts sand to 4 parts gravel), and the pointing should be done wioth a frost-proofed mortar, mixed at 4 parts sand to 1 part cement.

I'd lay all of this on a base of 150mm of 15-20 Newtons concrete, which would itself lie on top of a 200mm sub-base of granular material laid over a root barrier membrane. This gives us something around the 500-600mm thickness that seems to be the norm for ligt-use footpaths in areas where frost heave is a problem.

The granular sub-base and base layer of concrete could be laid first, and then the paving bedded directly onto the bedding concrete while it's still fresh. As ever, this is much easier when a semi-dry mix is used.

As I said right back at the beginning, you really could do with checking this with one of your compatriots as my experience of frost heave is minimal at best. However, assuming a frost prenetration of 450mm (18 in) this construction should be OK, and should be thick enough to resist interference from roots.

I'd be interested to hear how you get on!

LV Lishious
Sep 26th 2003
Didn't think of all that. Guess that's why your're called the "Paving Expert". Thanks.

I have only one reason I'd use the concrete panels as opposed to pouring a new concrete walk on which to lay the slate: expense. We've used the panels elsewhere by just laying them at ground level or just on top of ground and when interlocked with the tongue and groove they don't really move. Without the interlocking (which can't really be done end to end), I see your point that they'd be individual floating blocks. I don't think they weigh as much as nor are they as bound together as sidewalks poured with control joints. I had thought that laying each panel on a couple of inches of crushed stone wouldn't be much different than pouring a slab over a stone sub-base, but I guess not.

The reason I didn't want to dig into the root system of the tree is that the old maple and arborvitae are around 85 years old and the surface roots are like tree trunks. There are probably plenty more gigantic roots underground but I didn't want to damage the trees or make them more likely to fall on my house. So even if I pour a slab I'd form it above ground and then build up soil on the edges. Am I being too much of a tree-hugger here? Do old trees like a severe root trimming now and then?

The bottom line is that I can't afford a pour at this time: 65 sq. meters of 6 in concrete? Uh, no. So I may to have to settle for laying the slate directly on top of a shallow gravel base until the spring and then do the job more permanently next summer. I have a pile of gravel. I should be able to shovel the snow off of that path, and as long as it's flat people should be able to negotiate it safely. I could probably get a season out of it.

There's no comparable site on my side of the pond, and any do-it-yourself site addressing these subjects is skeletal at best. I'll refer to the other resources on your site to do a "proper job".

Thank you kindly for your advice.

Tony McCormack
Sep 29th 2003
I hope you manage to get your slate laid. If you take any photo's I'd be chuffed to see them, These 'Slate Mill Ends' sound very interesting.

You may be right that laying a temporary surface on gravel to get you through the winter could be the best option at this stage. I'm supposed to be meeting a US-ian paving contractor sometime later this month, so, if I can, I'll get him to give me a quick briefing on US methods that I could possibly turn into a page of basic hints.

With regard to your trees, if the maple is what we call a Sycamore, then the roots are fairly forgiving, as long as you don't take out too many, but the Arbor Vitae, which is a conifer over here, tend to have shallow, fibrous roots and you have to be more careful, as they rely on the fibrous mat for anchorage. If it's only a small tree, then it shouldn't mind a bit of a trim, but for anything more than 3m high, it's best to consult a tree surgeon.

LV Lishious
Sep 30th 2003
My Maple is a Sugar Maple (Acer Saccharum), not a Sycamore   (Platanus occidentalis). The Sugar Maple Specimen is so old that it's upper branches look like tree trunks. I'm sure it's not long for this world. The arborists can't really do anything with it, topping is out of the question, and so I'll nurse it along until it split open in some storm. I'll call my local agricutural extension service before I start cutting any roots.

I'll check your site for a North American tips page you put together. I just saw a do-it-yourselfer show where they were laying a path in California with big blocks of granite on a couple of inches of gravel and a few dollops of mortar----they then said basically "don't try this at home kids if you live in the colder latitudes...."

I'll see if I can get a picture of the slate mill ends --- my sister has a digital camera and knows how to download it. I don't think "mill ends" is a term of art but of commerce. When the quarry gets to the end of a run the stone will have a slice left and this is it. Also, when they cleave it and it's too uneven, it ends up in this pile. However, the local quarry sells it for $1 for each piece, no matter the size, so I even picked up the 2 x 2s for $1 each. Can't beat the price.

Thanks again for taking your valuable time to respond to my inquiry and maintain this wonderful site.

Tony McCormack
Sep 30th 2003
I see that BBC America has inflicted 'GroundForce' on your country, as though you don't already have enough troubles, and they are using the very same paving practices on US-ian projects that we use here in the UK.

I wonder if they'll ever get around to doing the Follow-Ups that we get over here? Basically, 12-18 months after they've made over your garden, the two eejits make an alleged 'surprise' visit to see if you're looking after the plants, or whether you've ripped up the bloody decking and painted the fence any colour other than blue. Given the problem with frost heave, which doesn't seem to be a consideration in their construction works, I doubt we'll ever get to see the twisted and broken paths, and the rumpled pavers that didn't manage to survive even one winter!

Looking forward to your pix!   smile

Forum Question Calder Brown Patio All Finished - Mark H - Sep 27th 2003
Just finished laying Marshalls Calder Brown Flags out the back path.

Laid on the old concrete path via 5 spots (sorry Tony!) followed by wet grout.

Levels were difficult as multi sloped.


forum answer Tony McCormack - Sep 30th 2003
Looks neat and tidy, Mark - well done! I'll say nowt about the spot bedding and the "4-corners meeting" at this stage! wink

How did the wet grout work for you? Didn't you find vast quantities of it disappearing beneath the flags because of the spot-bedding?

Mark H
Sep 29th 2003
Dead on Tony.

I had to "butter" each edge with loads of mortar..... and still I had to ram loads of mortar into the gaps with the mortar tool when pointing... it seemed to eat up all my precious and backbreaking mortar mix.   wink

All in all the spot technique was a bit of a pain as some of the spots were about 9" tall (before being compressed by the slab) when I tried to even out the levels a bit... and then kept lifting/re-lifting the slabs to re-spot correctly for levels.

The wet grouting left quite a bit of staining as I let it get on the slabs at first (my fault being a complete newbie).

The only way to get rid of the staining was to manual wire brush (I got through 4 wire brushes) and then wised up and used a moderate power tool with rotary wire brush attachment.

Trouble was, it started out as "I'll just lay 6 slabs" from back door to the shed" over the existing gravel on concrete path.... and ended up laying 107 slabs and doing the whole small yard/path   smile

A little way through I noticed the mortar staining and an internet search pointed me in here to see how to get rid of the staining......./ only then I saw the advice I really needed before I started.   smile

Rgds - Mark

Tony McCormack
Sep 30th 2003
Better late than never....almost!   smile
Forum Question Price of yorkstone - Razor11 - Sep 29th 2003
Please humour me.

I want to install about 100m² of paving (part driveway and part patio) around my house.

Ideally I would like Yorkstone (as I live in York), but I've been quoted £70/m² supply only.

So I am looking for alternatives and need help narrowing my choice down....and price expectation.  I would spend up to 3£0/m² for the stone itself.

My queries:

  1. Is Yorkstone really that expensive?
  2. I am open to ideas as to alternatives (stone/concrete) that looks similar, any suggestions/price?
  3. Ideas as to where to purchase in/around York?


forum answer Tony McCormack - Sep 29th 2003
1 - Yes: Yorkstone is that expensive, but, if you shop around, you can get it for around two-thirds of that price by taking a thinner flag (40mm) for the patio, and a 65 or 70mm thickness for the driveway. Reclaimed yorkstone can be had for 30-40 quid per square metre, for top quality stuff.

2 - There's a lot of imported sandstone on the market just now. It's not quite as good a real yorkstone, but it's only the anoraks like me that can tell!   smile

3 - Try Chris over at Bingley Stone. He has both Yorkstone and imported stone, and he's less than an hour from your place. Tel: 01535 273813

Sep 30th 2003

Where should/could I look for reclaimed Yorkstone at the prices your suggest? I emailed Bingley and got very high quotes (at the top end of my original quote, with reclaimed yorkstone the same as the new stuff).

Any other suggestions, or failing that, any good (reasonably priced) sources of good quality Indian stone local to me?

Thanks for the continued help.

Tony McCormack
Sep 30th 2003
What sort of quantity are you looking for?
Oct 1st 2003


Tony McCormack
Oct 2nd 2003

  • BBS in Wakefield - 01924 241100
  • Architectural Stone in Nelson - 01282 614966
  • Purpletree in Richmond - 01748 850896
Forum Question Is fall essential? - Mark H - Oct 4th 2003
For a 3m square paved area surrounded by 3 earth garden borders and one garden gravel path is it worth putting a fall on it?

I was going to just lay slabs dead level all way round and grout.

It's not as if it's going to collect large volumes of water and where the water does run to is not important.

TIA - Mark

forum answer Tony McCormack - Oct 6th 2003
Yes! It is worth laying the flags to a gradient, even over such a small area, otherwise you will be relying on hydrostatic pressure to drain the paving. This means that, as the 'level' of surface water builds up on the paving, it will exert a pressure which forces water to trickle over the edges and lose it self. The drawback with this approach is that you end up with a thin film of standing water for a period of time after the rain stops, and which turns to ice in the winter.

We lay ALL paving with a fall, even when it's only one flag wide around the house. It's just as easy to lay to a gradient as it is to lay flat - in fact, it's easier to lay to a fall!

Mark H
Oct 6th 2003
I know it's easier to lay flags with a fall.

Trouble is, mine fall all in different directions.   smile

Seriously, Tony thanks for the info and bothering to respond as usual.


Tony McCormack
Oct 7th 2003
We've had a few so-called Flaggers working for us who had just the same problem, Mark!   wink
Forum Question Flagging a driveway - Fraser P - Oct 6th 2003
What mix/strength of 'mortar' is recomended for bedding a car drive?

I'm having to lift and re-lay the flags (2" 2x3 and 2x2) on my drive and front path. Not a large area. 35m² in all. Due to cost restraints I have decided to use the following format:-

Sub base - 100 \150mm DPT1 or 50 mm Crusher
Bedding - 25 \50mm Mortar mix on drive

I had considered concrete base but the cost was prohibitive.


forum answer Tony McCormack - Oct 6th 2003
Use a relatively weak mortar for the bedding. A Class V mortar (1:8) is ample.

Under site conditions, we'd use a lime mortar, but this is not always possible for residential projects. Further, using a stiff bed over a flexible sub-base is less than ideal, but it's not critical on a residential driveway. Make the bed 35-50mm thick and you should be fine - you'll find that a semi-dry mix is much easier to work with than a wet mix, and you can use grit sand rather than building sand.

Fraser P
Oct 6th 2003
Thanks for the feedback. Probably a silly question, but..... you mentioned that  "Further, using a stiff bed over a flexible sub-base is less than ideal, but it's not critical on a residential driveway. "

Is it considered 'acceptable' to use a simple bedding on a subbase for a drive way? Clearly it wouldnt be as strong as mass concrete and mortar but is it a viable option?

I'm really after a simple do it myself fix.


Tony McCormack
Oct 6th 2003
The usual rule of thumb is "stiff on stiff: flexi on flexi" and so a flagged driveway (using pcc flags, not wet-cast decorative patio rubbish) would normally be laid using an unbound bed of grit sand.

However, some contractors prefer to use a bound bedding material, and so a weak concrete/mortar is just about acceptable. Using a high-strength concrete or mortar is a waste, so the idea is to provide just enough 'binding' to stiffen the bedding and prevent any minor settlement or erosion, rather than provide a solid base. Larger flags, such as you have, are less popular for vehicle overrun areas nowadays, as we would prefer to use something like the 400x400 or 450x450 Small Element Pavers, which are a sort of half-way between block pavers and big flags, but they are still used, and whether you use clean, unbound grit sand or a weak mortar/concrete as the bedding, as long as they are firmly consolidated when laid, they should be fine.   smile

Fraser P
Oct 6th 2003
So from your comment do you think a more acceptable formula for the drive would be:-

Sub base - 100 \150mm DPT1 or 50 mm Crusher
Bedding - 25 \50mm Grit sand

These old style paving slabs are PCC, V thick and V heavy, but thats what I have to work with. The previous laying lasted 30 years, and that was on a grit bedding. I'm going to do some test excavations to see exactly the state of the sub surface.

One more question, 'where to get' the sub base or bedding? Do you recommend going direct to a quarry or use a builders merchants? I may be needing 8 ton of Sub and 2.5 or 3 tons of bedding. I've never had to buy this before.

Thanks again

Tony McCormack
Oct 6th 2003
I'd be happy with your revised spec. There's no need to use a cement-bound bedding for this type of project unless there's a specific reason to do so, such as ground instability or excessive mining by ants.

As I've just replied to one of my email questioners...

"I recommend using a weak-ish sand/cement bedding mix for patio work because it's damn near impossible to get full consolidation of the bedding without breaking the weak wet-cast patio flags, but there's nowt wrong with using unbound, cement-free sand, for proper pcc driveway/highway flags."

As for buying your materials, unless you can buy in full loads (20T or more) the quarries are unlikely to deal with you, so you'll have to go through a BM.   frown

Forum Question Dry or wet mix for a step? - Bry - Oct 12th 2003
I'm part way through building a slightly raised patio, 450mm square textured flags on a 10:1 dry mix to be grouted later. They're built on one course of blocks. I've been individually bedding the flags and the dryness of my mix is rather erratic. I reckon I added water when I shouldn't. frown

Problem is, some of the flags have adhered to the bed and some haven't, in particular a few that are at the edge and overhanging the step-bricks are loose. What did I do wrong there, and how should I fix them? In fact, should they actually have stuck down at all? I still have lots to learn, so forgive my ignorance. When it's built, may I post you some piccies?

forum answer MRW - Oct 13th 2003
Good one - I am not the only one then. I've just laid block pavers for a path and some have stuck and some have not. It says 10/1 for slabs. Then on the ridged section 3/1. I did about 8 to 1. I did a fairly stiff mix then tapped down with a mallet. Where have I gone wrong? Have I not tapped down hard enough? Cheers great site
Oct 16th 2003
I use 4 shovels of sharp to 2 shovels of builders and 1 shovel of OP (cement), and make it pretty wet, then I lay on 2 inches of this mortar and have never had a problem with loose slabs or edgers. I find a wetter mix adheres very well and goes off in around 24-48 hrs. Yo u can use hardener if you are in a hurry, and in hot weather I use a plasticiser.
Tony McCormack
Oct 26th 2003
For flags/slabs, there's usually no need for the flags to adhere to the bedding. In fact, on commercial contracts, we use a lime-based mortar to ensure that any bonding will be weak and easy to break should the paving have to be lifted for whatever reason.

The only time you would definitely want the flags to bond to the bedding is where one or more edges of the flags are 'free'; that is, they are not abutting any other flag or a fixed object such as a wall or manhole cover. This can happen with a typical patio or other pavement at the edges, but, in the vast majority of jobs, there's no need to bond these edge flags to the bedding as the forces they encounter are minimal and easily contained. However, in those scenarios where the edge of the flag is exposed, or overhangs a sub-structure, such as a step, then it is a definite advantage to have the flag bonded to the bedding, purely for reasons of safety.

If a point load (ie, a person) is applied to the overhanging edge of a step, then there is a possibility that the whole flag could pivot and flick upwards. This possibility declines with larger flags, smaller overhangs and lighter point loads, but it is good practice to create a bond in these situations, just to be on the safe side.

A good bond can only be achieved between a reasonably wet/tacky bedding material. You can't get a good bond between the underside of a flag and a semi-dry or dry mix, and so a wetter mix, such as that described by Suki, would be ideal for use at the edges of pavements or when constructing steps, even though it is (in my opinion) much harder to work with elsewhere in the pavement.

So, in summary, I would only ever use a wet bedding mix for step treads and/or for pavements where there is a real chance of flags at free edges slipping out of place. Elsewhere, I'd use a semi-dry mix.

To Bry, the original poster, you're more than welcome to send in piccies of your efforts, and pass on anything you've learned from the experience.

To MRW, the second poster in this thread - I've no idea what you're on about!

Oct 26th 2003
Cheers Tony,
I've lifted those few flags and used a stronger wetter mix: They seem well stuck now. That said the overhang is only ½ an inch, so I'd probably have been ok anyway.

The project, affectionately known as "Bry's bandstand" is coming on nicely, I laid the last cut bit of flag today, and have just to add some coping to the wall, then lots of grouting. Dark nights, weather, and having a day job are all detracting, but I'll be sure to post you some pics, 'cos I'm well chuffed at my first bit of building. smile

And Yes, I've learned a few lessons, some painful, which I'll relate later.

Now I've got the bug, I can see myself ripping up all the garden and building an aerodrome. Maybe next year though for that, when I've got a new wheelbarrow.

Regards - Bry.

Tony McCormack
Oct 27th 2003
If you're a good boy, Santa might bring you a new barrow.  wink
Forum Question Whinstone paving and river sand bedding - Birch R - Oct 16th 2003
I have nearly laid the front driveway 50m square, I used the above flags in two sizes trying to make it look like it had been down for years 2x2 and 2x1.

I started off by breaking all the concrete up with the help of a Kango and loading three skips two 8 ton and one 4 tonof mostly concrete and a little soil. I then proceeded to apply the crusher run after using 4 ton and a machine to hammer it flat (vibrator) I left it for two weeks, then went over it again to see if it went down any further.

I was then ready to start laying the flags I went to order 5 ton of 3/8 stone and grit sand, but was informed that RIVER sand would be more suitable, the mix of RIVER sand and cement was to be ½ bag cement and fill the mixer (Baby Belle) and not to make it to wet.

This I have done and the final flags should be laid either tomorrow or Saturday depending when the supplier can deliver the last 17 as I used all there stock of 2x1's. The flags seem very solid, but alas I haven't drove the car on it yet?

What are your views of laying flags on RIVER sand?

forum answer Danensis - Oct 17th 2003
I'm sure Tony will add his two penn'orth when he gets back from his hols, but I would expect soft sand to wash out more easily than sharp sand.
Birch R
Oct 18th 2003
Hi Danensis

Thanks for the quick reply, I have had a look at what I have already laid as I am still waiting for the supplier to deliver the last 17. The sand has gone rock solid and I mean rock solid the colour has gone BLACK and a hammer and bolster was needed where I had left a little overhang.

Tony McCormack
Oct 26th 2003
River sand is a loose term. Some river sands, such as the Mersey grit we have around here, are great for bedding and concreting, but other river sands, such as one I saw in Bristol, is too fine, too silty to be an ideal choice.

However, it seems that you are reasonably happy with yours, so we'll sy it's OK. But for future reference, it is the class of the sand, whether it's a coarse, medium or fine sand, that is important, not its source. For bedding and general concreteing, we prefer a Medium (Class M) or Coarse (Class C) sand.

Forum Question Can I Wacker me flags? - Urmate - Oct 20th 2003
Help help! This is my first visit to this site and its helped big style. I am laying flags to my back garden, so far so good, I have screeded and laid flags but I need to know if I can use a Wacker on 900x600x60 flags? Some say it will break flags, some say use an old blanket. Anyone help? Ta very much
forum answer Paul Challinor - Oct 25th 2003
Don't use a Wacker on flags, they should be mauled, or if you can't get your hands on one of these, use a piece of 4x2 timber and a lump hammer, to firm them in. Concrete without steel inserted is very fragile.
Tony McCormack
Oct 26th 2003
Paul's right: you cannot use a plate compactor on the larger sizes of BS flags, and never on any of the wet-cast decorative patio flags, even with a blanket!!

You can use a plate compactor to consolidate Small Element Paving units, which includes specially manufactured BS flags of 450x450mm or smaller, as well as the usual block and brick pavers.

For D50s (900x600x50mm) you really do need a maul. The little rubber mallets (we call them 'clonkers') are too lightweight, and the plate compactors will snap them like Arrowroot biscuits at a WI coffee morning!

Forum Question US Flagstones on Mortar - Mr Mayer - Nov 3rd 2003
I mortared the upper level of my new flagstone patio last weeked. The pieces were not very large (around half a square meter) and it was not easy.

Next up I need to mortar the lower level which is five times larger. Also, I used larger flagstones, with some of the pieces being as large as 1.25 square meters, and require two fit men to move. Here's a pic of the lower level (obviously a work in progress, and I have a few more pieces to cut):

mayer patio

So, are there any tips on how to do set these stones in mortar? I think that it might be impossible for us to lift them up once they are down in the mortar. We had to do that twice on the upper level and I do not want to have to do that with these larger stones. It might not even be possible.

Also, my wife just came back from a tile store and they wanted her to buy this sealer that costs $250 (170 quid) per gallon. That does not seem right.

Any advice?

forum answer Tony McCormack - Nov 4th 2003
I used to have a Chinese puzzle game that looked a bit like that patio!

When you say that you need to 'mortar', what do you mean exactly? Do you mean bed the pieces of stone, joint them, or both?

If it were my job, and the stone was being laid onto wet morrtar, I'd screed out a bed using a short length of timber, and try to set the level just fractionally higher than 'spot on', say 3-5mm high. By screeding the bedding, you ensure that you've got even coverage and that there are unlikely to be any voids once the flag is in place. Ripple the top of the screeded bed using the stick or a trowel, so that there's room for the mortar to adjust itself to any uneveness in the base of the flag when it's placed.

Once all that's done, get a couple of handy lads to lift the flagstone gently into place and tap it down using a small rubber hammer (a "clonker", as we call them in Culcheth). Check for any wobble, and if necessary, lift and re-bed.

One problem with laying larger pieces of thin flagstone or slate onto a wet mortar bed is that it can be difficult to lift the stone free of the mortar if adjustments are needed, as there is a tremendous suction created with a wet mortar. However, if you have a couple of lengths of 10-12mm steel bar, these can be slid under the offending flag and used to lever up the stone from beneath, so that there is much less chance of straining your back or breaking the flagstone.

Getting the bed right on the first attempt is, obviously, the best way to proceed, but, when you're working with a naturally variable product such as stone or slate, the best you can do is guess. Your guesses become more experienced with practice, and my dad, now almost 70 and into his 6th decade of flag laying, now gets the bed right almost every time!

I can't comment on the price of the sealant as I don't know what prices are like over there. 170 quid for 25 litres of a top quality sealant is not unusual in Britain, I have to say, but, to be honest, I wouldn't be thinking about sealing that stonework until the spring. I prefer to give the mortar a chance to exude all the efflorescence, and to make sure there's no movement or problems. Is it normal to seal flagstones in your part of the world?

Mr Mayer
Nov 4th 2003
Thank you for your great advice (again)!

I'm trying to bed the flags in mortar. I was thinking that the correct thing would be to joint the flags with a similar colored (slightly darker than the flags) grout. The flags are going on top of a 2.5cm thick layer of concrete that we poured about a month ago.

The size of the main level is around 185 square meters.

The 170 quid was for only 4 liters (actually less than 4 as I'm talking a US gallon), not 25 as you mentioned.

I live about 30 minutes from Aspen, the ski town, and our property is around 6000 meters in elevation. So the sun is a lot closer and we normally get 8-9 meters of snow over the winter months. I hear different stories about sealing. Some say let it wear naturally. Some say seal early and seal often (annually) and some say seal every three years. Some say seal before grouting, others say seal after grouting.

Personally I have not seen what unsealed flags looks like after, say, a few years. My guess is that they would deteriorate significantly if they were not sealed. I do not know when to seal, how often or what is the preferred type of sealer. I'm not a huge fan of the high-gloss finish look.

In any case, I get so many opinions and they are all completely different, which baffles me. I would think that there would be a basic way that these kinds of things are done, with "general rules of the road" to be followed. I'm not sure that is reality, though.

As always, your sage advice is appreciated. Now if I can just keep Old Man Winter away for another week I might have a chance to wrap this project up.

Nov 5th 2003
Would the idea of using banding straps work for flags? It certainly made laying kerbs a lot easier, and the straps just slide out once the levels are right (or you can just cut them off and leave them in situ).
Tony McCormack
Nov 5th 2003
I think that using a darker mortar to joint the flags is a good idea. In my opinion, a bright mortar distracts the eye from the stone, which is, after all, the supposed focus of a patio, whereas a dark mortar shrinks into the background, drawing no attention to itself, while 'framing' and accentuating the flags themselves.

I don't know what to recommend regarding the sealant. Personally, I think 'varnished' looking flags are awful and so, if I am ever asked to recommend a sealant, I opt for one of the 'invisible' types that have no obvious effect on the surface of the stone. However, some folk like the 'wet look' as it does empahsise the colouring of the stone.

This is further complicated because I have no idea of which sealants are used in your country, how they interact with the stone, and what effect the elevation and weather in Aspen has on the paving over the longer term. If all of your neighbours' patios are sealed, then that would suggest that it is a received wisdom that sealing, somehow, improves the performance and longevity of the stone. With a laminar stone, the repeated freeze-thaw cycle would be catastrophic, but it may be that the stone you're using is non-laminar or is, in effect, "frost proof" - I simply don't know.

I think I would be tempted to seek out a satin or matte finish selant, or see if there are any that have no discernible effect on the appearance of the stone. I know that one of the better quality sealants used with native British stone is manufactured by Dow, which is, I believe, a US-ian company, so they must have summat similar over there!

Forum Question Patio over existing concrete base? - Andy Benno - Nov 5th 2003
I want to lay a new patio using pavers on an existing concrete base approx 8m x 5m. The new patio'd area is to cover roughly the same area (maybe extended about 2 ft on the lawn side) and I am wondering whether this existing concrete base is suitable to pave over or whether it will have to come up and I start again from scratch.

The concrete looks as if it is between 1½ - 3 inches thick in different places, it is pretty solid but has some cracks of approx 3-8mm running thru it in various places. Where these cracks occur the levels of the concrete can change by up to about 10mm. I would also say that the levels across the whole 40 sq.m may vary by about an inch.

What I need to know is can I flag over this and if so, how should I prepare this ready for flagging?

forum answer Tony McCormack - Nov 5th 2003
As this is only a patio, I reckon you can safely flag over the existing concrete, but you need to check that there won't be a problem with the "150mm below dpc" rule.

You can lay the flags on the usual 10:1 semi-dry mix of grit sand with cement, and ensure there is adequate fall away from any buildings.

Essential preparation includes setting up string lines to act as level and line guides, and to check that you have sufficient room on top of the existing concrete base to accommodate 30-50mm of bedding plus the thickness of the flags you plan to use. Other than that, just make sure you clean off any crap that's on the concrete, such as weeds, litter or detritus. There's no need to clean it with a power washer or to use a bonding agent - it's acting as a rigid base layer, and adhesion is not essential.

Nov 6th 2003
I would have some concerns over this. If the existing concrete is over clay, and has already settled, there is a real risk that the concrete will continue to move, and the patio will end up with differences in level following the lines of the original cracks. This will especially be the case if the movement is caused by tree root dessication as the matter will get worse if the offending trees are not kept lopped.
Tony McCormack
Nov 6th 2003
It depends on the age of the existing concrete, and whether there's been any recent movement. If the ex. conc is realtively satble, laying over it is a cheap'n'cheerful option, as the cost of bringing in a skip and breaking out the concrete can be prohibitive on small, patio jobs.

Reflective cracking is not likely to occur on a flagged patio - if there was any movement of the concrete base, then the flags and the bedding would move with the base, relying on the jointing to absorb such movement. Only if the flags were well and truly bonded to a bedding medium that was, in turn, well and truly bonded to the concrete base, would I expect to see any reflective cracking, and even then, I'd be surprised!

If we assume that the concerete base is stable, or relatively so, then taking a chance that any future movement will be small and would either be insignificant, or of such a small magnitude that simple 'lift and relay' in the area of any movement would be sufficient to rectify is probably a better option that splurging out x hundred quid to break out and cart away what's already there.

Forum Question Re-colouring rained-on mortar - Fat Dog - Nov 10th 2003
Hi Tony,
I recently completed laying my patio and due to various reasons had quite a bit of catch-up pointing to do. I had been using Blue Circle's Snowcrete with a hint of buff cement dye and a fairly orange-ish sand. This produced a good mortar colour that really complemented the slabs (i.e. a very, very pale yellow-orange). Unfortunately and out of the blue, just after I'd finished the pointing, the heavens opened up and the patio got a good soaking. When the rain stopped and the patio dried, I have frustratingly found that the mortar is not now the colour intended. It is now many shades of boring grey, ranging from very dark grey through to an almost whitish grey, but certainly not the very light buff intended. The final colour seems to reflect how long the mortar was laid before the rain came. Luckily, the slabs don't seem to be affected (i.e. no cement or dye has washed out onto them) and the mortar appears very strong.

So, now the questions - Is there any way of colouring the already laid mortar to make it the very pale buff colour intended? Chiselling out the mortar and re-doing it isn't really an option as the patio is nearly 15m2 in total. I had considered mixing some dye in some water and kind of painting it on the existing mortar and hoping it would slowly soak into the mortar, dyeing it as it did so. Not sure if this would actually work and in any case, because the mortar now ranges from dark to light grey, might I just end up with mortar that is dark to pale buff? The slabs are Bradstone's Gironde and are a whitish-yellowish colour. Grey mortar looks truly awful with them.

PS I had never tried a project like laying a patio before, and did so using only the advice given on this site. The result is truly professional-looking (apart from a bit of bad luck with the pointing) and is testament to the quality of this site. Thanks for all your time and effort.

forum answer Tony McCormack - Nov 10th 2003
Is there any way of colouring the already laid mortar?

No. 'Fraid not.   frown

You could top it up, possibly, with a fresh, coloured mortar, or use an epoxy-based colouring, but neither are guaranteed to be successful. Mixing the cement dye with water will not work - the dyes work by reacting with and colouring unhydrated cement. They do not work with hydrated (cured) cement or cementitious products.

Have you got a photo of how the pointing looks at the moment? I might have an idea how you can get the desired effect, but it depends on joint width and pointing depth.

Fat Dog
Nov 10th 2003
Thanks for the prompt reply. The patio was laid using 6 different sizes of slab, so it was necessary to vary joint widths as I went along to get everything to fit (as a bonus I also found that this further randomises the random effect of the paving). Hence, the mortared joints vary from as little as 4 or 5mm up to around 15mm. Joint depth is 40mm. I don't think there's really the room to top it up with fresh mortar, certainly nothing more than about a 1mm "skim" on top - would that be enough?

I'll try ang get some pics of the way things look at the moment, but I'll have to rely on the digital camera using the flash, as I'm at work during daylight at the moment.

Thanks once again.

Tony McCormack
Nov 10th 2003
With only 1mm available on top of the joint, I'm not sure it would work. I was thinking that, if you had 4-6mm or so, a coloured wet grout or a pumped mortar might have been viable, but you need a minimum 3mm of mortar to give it any real strength.

You do realise, don't you, that in 12 months time, the joints will all be a dirty 'detritus grey' anyway!

What about a masonry paint?

Forum Question Adequate fall on riven stone - pkarees - Nov 10th 2003
We have recently had two areas of riven stone paving laid. They both extend 7 m from the house. We have a fall of 30mm on one and 45mm on the other. We feel the fall is inadequate but the contractor says there are no British standards and the fall is OK. He also says that recommendations in books are for DIY purposes and not professsionals. Comments much appreciated.
forum answer Tony McCormack - Nov 10th 2003
There are no British Standards specifically for patios, but BS 7533 Code of practice for construction of pavements of precast concrete flags and natural stone slabs states:

"A minimum longitudinal fall of 1.25% and a minimum crossfall of 2.5% are recommended for carriageways using paving units as a channel. For other areas a 1% longitudinal fall and a 1.25% crossfall are recommended..."

A patio would be classed as an 'other area' and so a fall of 1% longitudinal would be the minimum acceptable.

Actually, as these are riven patio flags, which are a bugger (technical term) for holding surface water, a minimum fall of 1.7% would be better, and I'd prefer to see a fall of 2%

30mm over 7m is 1:233 or 0.04% and 45mm is 1:155 or 0.06%, neither or which are acceptable for any form of paving.

Ask your erudite contractor which "books" are to be used by professionals. I'll bet he can't name them! (this is a bit of a trick questions as the 'books' are actually BS publications and Spec for Highways Works, but just how far these standards can be applied to patios and driveways is a moot point!)

Forum Question Spot-bedding and pointing - Peter W - Nov 14th 2003
I'm laying a fairly large (75sq m) patio of Indian sandstone on a concrete base with an average 40mm mortar mix at 6:1. In my first few stones, not knowing any better, I used the 5 spot method, although they were very large blobs which mostly merged together when tamped down. Having read you site however, I'm now on the full mortar bed but those early stones (only about 6) plus one or two of the larger later stones (1.2m x 0.56m) have a hollow sound when you tap them.

I found your archive post which describes the problem and my question is simple. Would you recommend taking these up and relaying or would you leave well alone until something goes wrong? They appear very firmly fixed at present and the large ones are a devil to do!

Second question on the learning curve: I used my 6:1 mortar also for pointing on those early stones but then found your recommended mix of 4:1. Again, am I likely to have problems with a 6:1 mortar in due course, or is it just a case of wrong, but not that wrong?

forum answer Tony McCormack - Nov 14th 2003
I think I'd leave the spot-bedded flags for now, Peter. It may well be, as you say, that the mortar dabs merged to some extent, and are supporting the flags adequately (for foot traffic). Lifting and relaying may not achieve anything other than getting rid of the hollow echo.

The pointing is slightly more problematic, because the difference in strength between the 6:1 and the 4:1 may make itself apparent as a colour difference. Strength-wise, I wouldn't worry because mortar-bedded flag paving relies on the bedding for its competence, and the jointing is primarily a matter of "filling a gap", unlike other paving types, such as cubes or cobbles, where a large part of the pavement's structural integrity results from the jointing strength.

So, unless there's a glaringly obvious colour diff between the two mixes, leave it alone. Any minor shade diff will disappear as the mortar weathers, and, looking out of my window, now really isn't the time of year to be doing more pointing than is absolutely necessary!

I have a sneaking suspicion that the above is what you were hoping to hear!   smile

Peter W
Nov 14th 2003
Thanks for the very prompt and comprehensive reply Tony - and yes, it was the right answer in both cases! The pointing mortar colour is a little different but as you say, it will weather.

I will continue with renewed confidence - though I am amazed how long it all takes as a result of which I am indeed doing laying and pointing in these dismal days.

A couple of more questions Tony:

I was cutting an awkward shaped stone today and the last cut (it is always the last cut) resulted in a hairline fracture down about one third of the stone length and visible on both sides (with close scrutiny). The stone seemed otherwise sound so I laid it anyway. Do you think that the stone will eventually crack - possibly as a a result of water ingress and subsequent freezing - and therefore is it best to replace it sooner rather than later?

Second question: in cutting a large curved edge to a patio, is it better to lay the stones and cut 'in situ' or dry lay first and cut individually before bedding?

Thanks once again!

Tony McCormack
Nov 18th 2003
If a hairline fracture is showing on both upper and lower faces, it can only be a matter of time before it breaks completely. Once the frost gets into it - blam! If you can get a replacement flag, you might as well get it changed asap.

When it comes to cutting a large radius curve at a free edge, I'd much rather lay all the flags and then cut in-situ. If you do a dry lay, mark and then cut before final bedding, you can guarantee the abstrads won't align that way again and you end up with a dog-legged curve!

Forum Question Bedding and jointing crazy paving - Stephen Taylor - Nov 26th 2003
I plan to lay bluestone crazy paving on a pre-laid reinforced concrete bed. I have both a patio and carport to cover. The stone is of variable thickness but is thicker overall for the carport.
  1. I have gathered from the forum that a 10:1 cementitious bed of 30-50 mm is ok for the patio - can you confirm this?
  2. Should the same apply for the carport?
  3. The dry sand jointing approach has a LOT of appeal effort-wise but will it stand up as well as mortar, and won't it be susceptible to weeds and moss etc?

Any other suggestions?

forum answer Tony McCormack - Nov 26th 2003
10:1 bedding for the patio area is fine. You can also use this for the car-port area, or you can beef it up a bit to 8:1. Use a semi-dry mix - it's much easier to work with.

I can't recommend dry-sand jointing. That would be flexible jointing on a stiff construction, which just doesn't work. You need proper mortar jointing. This is especially so with 'crazy' paving, as the joint width is so variable and sand joints are only suitable up to 5mm width.

If you really want to avoid mortar jointing, a polymeric sand might be suitable, but it can work out to be quite expensive if you have a lot of paving to joint.

Stephen Taylor
Nov 14th 2003
Thanks for the info. Nothing for it but to go and buy some kneepads!
Forum Question Bedding mix for edge of path - Gary N - Nov 27th 2003
I've just completed a path using slabs and used a 10:1 bedding mix. One edge of the path is 'free/exposed'.

The mix was quite tacky with water and plasticiser added. Do you think this will provide adequate adhesion to the edge slabs once fully hardened, or is the mix too weak to provide a good bond. I don't want the edge slabs flipping up! If they prove to be loose would you recommend chipping away just the top of the bedding and relaying using a thin layer of wet stronger mortar?

Regards - Gary

forum answer Tony McCormack - Nov 27th 2003
I think that you've probably got sufficient adhesion to prevent lateral, movement of the flags. This free edge: is it completely open or is it backfilled with soil/garden/summat else?

If you have an exposed edge, that is, one where the edge of the flag and possibly the bedding, are open to view, then having the edge units bonded to the ebdding is a good idea, but if there's soil etc. there, covering the edge, then it's less critical.

If they do prove to be loose and moving, then the simplest remedy is, as you say, the scutch off the top 20mm or bedding and lay on new Class II mortar for certain adhesion.

Gary N
Nov 29th 2003
Thanks for your quick reply Tony. The edge, including bedding is open to view. I'll see how they've bonded and remedy if necessary.

Regards - Gary

Tony McCormack
Nov 30th 2003
I uploaded a new page last week looking at a couple of strategies for laying flags to free edges. You might find it interesting.
Gary N
Dec 2nd 2003
I've had a read of your new web page. The edge slabs seem to have bonded okay so it appears the damp 10:1 mix with plasticiser has done the trick!

Thanks again - Gary

Dec 3rd 2003
One trick I've learnt with coping stones is to get them really wet before laying them, they seem to stick to the bed much better that way, I guess they have more suction.

Doesn't stop the b*****s nicking them though frown

Forum Question Flags over a lawn - Chris Glass - Nov 14th 2003
We are deliberating in creating a semi permanent area in the garden (lawn) and lay concrete flags in an area of approx 4mx4m. At the moment it is established lawn, however the area is to be used as a kennel with a run for a couple of dogs.

I don't want to make anything too permanent ie bedding it in with mortar, but would appreciate any suggestions. Ideally I would like to put some sand over the grass and lay the slabs, and secure the edges somehow.

Many thanks - Chris

forum answer Tony McCormack - Dec 5th 2003
You have to get rid of the grass, even if it's a temporary area of paving. If you were to go ahead and lay directly over the turf, the buried grass would degrade and decompose in a matter of weeks, leading to settlement of the paving.

Best to skim off the turf, take out 50mm or so of the topsoil and then lay the flags as described on the main site. If you wanted to protect the soil, you could lay a separation membrane over the exposed area before placing the beding material, but, if you use a good, clean, grit sand, the soil won't suffer if you miss out the membrane.

You can store any excavated topsoil, just in case you do decide to re-lay the grass, but as for the turf itself, that is best stacked and left to rot down to what gardeners know as a 'good tilth', that is, a fine, high-quality soil that is ideal for all garden tasks. You'll have to buy new turf, or to seed the area, if you choose to revert to lawn.


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