aj mccormack and son

Sitework - Page 03
The Brew Cabin


spacer spacer spacer spacer spacer spacer
Forum Question Sleepers as a retaining wall - Office boy - 19 Nov 2002
I plan to use some sleepers as a retainer and have read up about the preparation, technique and so on. Only snag is I cannot get hold of any mild steel dowel to secure the sleepers together.
Any suggestions ? Is there a nationwide supplier?


forum answer Tony McCormack - 19 Nov 2002
Any steel stockist should have steel dowels, look in Yellow Pages for Reinforcing Steel or Steel Stockholders. Alternatiovely, you could try asking a local building company, as they are the sort of item that nearly all builders and contractors have lying around, cluttering up the place.  If there's a new housing site or other construction site near your house, you can almost guarantee they'll have steel dowels or steel bars (such as T12, T16 or T20) that can be cut up into steel dowels, and you should be able to blag some in exchange for a few beer vouchers. smiley

You could also use steel road pins, which are sold via most Builder's Merchants for around a quid each.

Forum Question Backfilling a trench - Concrete Chris - Nov 25th 2002
At the weekend I dug a trench (12' wide) for some armoured cable (about 20m). Where I was digging had old compressed planings on top and earthy rubble underneath. I dug to a depth of 18 inches and then laid the cables in 5 inches of concrete as the trench crossed clay and then flint and chalk. I backfilled and then put the planings back on top.

All was happy until I noticed that the near the lower end of the trench was boggy (for about 2m). The end of the trench was ok. I compressed it and filled with some spare scalpings, but it remained slightly boggy. The rest of the trench surface is hard.

If I dig out the boggy part down to the concrete and fill the hole left with just scalpings will it provide a solid surface? I also have some stone spare if that would be better underneath.

Thanks - Chris

forum answer Tony McCormack - Nov 25th 2002
Simply excavating and backfilling can make a trench seem 'boggy' when it's actually just 'disturbed'. If it's not settled down in a day or so, then maybe you could try excavating the softer stuff and backfilling with stone, or you could simply cover the affected area with a membrane, if you plan to pave over the top.

When backfilling, do it in layers not more than 200mm deep. Compact each layer before moving on to the next, and work your way to the top in a succession of such compacted layers.

Concrete Chris
Dec 5th 2002
Dug the boggy bit out and followed your advice about compacting every 6 inches.

It worked like a charm.

Thank you

Forum Question Exposed Gas Pipes - Toplambs - Dec 8th 2002
I am preparing to lay block paving and have exposed the gas supply pipes to the house. They are at an approximate depth of 18 inches below the existing paving. The pipes are laid in heavy clay.

Is there a minimum depth that the pipes should be buried beneath the block paving/sand/sub-base?

forum answer Tony McCormack - Dec 9th 2002
There isn't a statutory minimum depth for service pipes (the pipes linking the gas main to your home), but 450mm is a typical depth and nothing to worry about. More worrying is just why you've exposed them at all at that depth. Most residential paving only needs an excavation depth of 200-250mm. Is there a specific reason why you've gone down so far?

Anyway, surround the exposed service pipe with sand, cover it with marker tape, if you have any, and backfill the trench with DTp1 or other suitable sub-base material in layers not exceeding 200-225mm in thickness, compacting each layer as you proceed.

Dec 9th 2002
The existing slabs that I am replacing are only about 2 inches below the damproof course and there is some damage to the mortar on the house brick work at or below the level of the existing slabs. I intended to excavate to a greater than normal depth to repoint the exposed brickwork and then ensure that the replacement block paving is laid at a lower depth than the slabs are currently below the DPC. Does this seem sensible/am I going about this the right way?
Tony McCormack
Dec 9th 2002
Aaah! I see. I'm not sure how beneficial sub-surface re-pointing is: you could use a damp proof membrane if damp seems to be an issue, but I don't think you'll do any harm.

When it comes to the paving, make sure it's at least 150mm below dpc and follow the tips I gave previously on backfilling in layers.   smile

Forum Question Bunny Proof Fencing - Moomog - Dec 13th 2002
I am doing a landscaping NVQ and am working with my brother. I was aked today about a rabbit proof fence for a lady in the country who wants to grow some veggies.

How deep do you need to bury the wire to keep out our long-eared friends?

Thanks for a great site - it's a mature students dream! smile

forum answer Tony McCormack - Dec 15th 2002
I think the usual recommendation for rabbit fencing is 450-600mm buried and 900mm above ground.

It must be 20 years since we last did any rabbit-fencing, but I don't think they've learnt to dig deeper or jump higher in that time.   smile

Mar 12th 2003
Hi Moomog

I have done a lot of rabbit netting on farmland and have found that rather than burying the bottom 450-600mm, as Tony says, it is just as effective to simply fold this amount out onto the ground at the bottom of the fence and, using old bits of fence wire bent into a U shape, pin it to the ground. Make sure the rabbit net is fixed and folded out to the side of the fence the rabbits will be coming from. It is a lot easier and at this time of year the grass will soon grow through the pinned down net and the rabbits will not bother it.

Max Ali
Mar 13th 2003
Thanks for that Johnboy. It makes real sense. My wife is about to do some in the next month and this will save her getting me to dig down so she can lay the fence
Forum Question Vertical sleepers - Lemoncactus - Dec 23rd 2002
I need to produce a construction drawing for a semi-circle of railway sleepers sunk vertically into the ground to create a screen. I'm having trouble locating information on the specific depth to which they should be buried in the ground. Can I follow the basic details of sinking concrete fencing posts or is it more complicated? Any clues?
forum answer Tony McCormack - Dec 24th 2002
A good general rule of thumb for this type of structure is "one-third buried". So, for a 2.4m sleeper, 800mm would be buried - I think you'd probably be safe enough with 600mm buried, as long is it's good ground.

A typical fence post has 1.8m above ground and 450mm buried, which is only one-quarter.

Forum Question Incredibly Deep Concrete Raft - El Guapo - Jan 1st 2003
I am trying to construct a brick built garage in my back garden to replace an existing garage and shed. The garage size is approx 12' by 24'. I had plans drawn for the garage by a structural engineer (for no other reason than to show a builder what I wanted) who stated that I would require footings of 2.7m.

He also offered to draw plans for a concrete raft for an additional £250, which I am reluctant to do. The reason he gave for the footing depth was that there is an oak tree about 50m from the garage position and the ground conditions are clay. Having read through this site I would be extremely grateful if someone could advise me on the best course of action and if there are any builders who wish to quote on this project please feel free to e-mail me.

forum answer Tony McCormack - Jan 2nd 2003
Is this a garage or a nuclear processing plant? 2.7m???? That's got to be a piss-take.   frown

Contact your local Building Control Office (BCO) and ask them to recommend a local draughtsman/engineer/architect who will flog you an 'off-the-shelf' plan for your area. As a rough guide, most rafts are less than 1.5m deep and I wouldn't expect a raft for a single storey garage to be any deeper than that.

Forum Question Hoggin for fill and/or sub-base - Jonathan Graham - Jan 4th 2003
We are restoring a disused quarry, waste-tip and factory area and building a house in the middle of it in (very) rural Norfolk. The (rather large) area immediately surrounding the house which will need hard surfacing is around 1000 square metres.

Most of this area has been previously quarried and backfilled with as-dug hoggin (flints 50mm to 200mm diameter running in clayey, silty sand) - so we're piling through it for the foundations.

The hoggin becomes pretty solid and inpenetrable when compacted (my 3-tonne tracked excavator just about hacks through it) - and just about impermeable too, due to the high clay content of the sand. It makes very serviceable site roads (sorry, paths and driveways) when run over a few times.

Will this material work as sub-base for stone paving? We need to add up to frac12; a metre to existing levels, and I have almost infinite quantities available. We intend to re-grade the area and install appropriate drainage and use the hoggin as a working surface for a couple of years while we save up for the stone (and while any poorly compacted areas settle) - but should we allow for say 100mm of type 1 on top or can I just spread screeding sand straight onto the hoggin?

Thanks anyone!

PS great site.

forum answer Tony McCormack - Jan 5th 2003
I have a great distrust of hoggin. I know there's some good stuff out there, but there always seems to be a lot more crappy hoggin that turns to a claggy mess as soon as you put your faith in it.

However, from what you say, I think you might be ok using your on-site hoggin as a capping layer, to elevate levels, and then see how it goes. If, in a year or so, when you're ready to install the final paving, that would be the time to determine as to whether a  layer of DTp1 might be advantageous. If the hoggin has behaved iteslf, and hasn't turned to goo or settled too badly, then a simple regulating layer of DTp1 or similar quality material might be all you need.

Forum Question Persistent weed - Apprentice - Jan 6th 2003
Hi Tony,

I've got a nasty weed on my driveway which I believe is known as "mares tail". I'm told the roots on it go down a long way. As sodium chlorate has failed to kill it off, have you got any ideas how I can get rid of it?

forum answer Tony McCormack - Jan 7th 2003
Mare's Tail, also known as Equisetum, has been around since before the dinosaurs, and it's virtually impossible to get shut of it. It's roots can go down for several metres - I've seen roots at 5 metres depth and I've read stories of it being as deep as 20 metres. Apparently, it was deliberately planted on some railway embankments in the Victorian era to help stabilise the earthworks!

When we know in advance that Mare's Tail is present on a site, we use a membrane such as Terram 1000 or TDP115, laid between the sub-grade and the sub-base, to keep it out of the paving itself, as it cannot force its way through a non-woven membrane. However, all that happens is the damned stuff travels along underneath the membrane and emerges at the sides of the pavement!   frown

We have had clients who have successfully eliminated it from their patios and gardens by repeated poisoning with Sodium Chlorate or Glyphosphate (eg Round-Up), by cropping it as soon as it emerges, or by blasting it with a blow torch every couple of weeks, but it's a long term task, not something that works in a month or two.

If someone does come up with a miracle cure, they'll have guaranteed their fortune, especially if it can deal with Japanese Knot Weed as well!

Forum Question CBM sub-base - Kathryn - Feb 12th 2003
What is the difference between a lean mix concrete and CBM?

I am currently looking at the sub-base for an external slate finish street, and it is my understanding that CBM is dry/damp mix of stone and cement normally used in road construction and which has an open texture. "Lean mix" on the other hand is a building term used to describe a wetter concrete mix which has a closer surface finish, but the term is fairly vague, as far as strength terms.

There will be a damp proof layer contained within the street construction, so a smoother surface on which to set this would be better, rather than an open texture which would be hard to bridge. Can you please tell me if I can find a spec to define lean mix.

forum answer Tony McCormack - Feb 12th 2003
"Lean Mix" is one of those terms that litter the building trade and is particularly unspecific. It simply means a concrete with a low cement content. That cement content may be as low as, say, 80Kg per cubic metre, or up around 200 kg per cubic metre, but, as I said, 'lean mix' is a very, very loose definition.

It is normally supplied at a low slump, but there's nothing to stop it being poured at, say, a 50mm slump and floated-up to give a close, smooth finish, but, because of the affect of the water/cement ratio, the 'wetter' a concrete, the weaker it is, and, with an already weak concrete, it can compromise the competence of the concrete if it's 'wetted-up' without prior consideration being given to the 7 or 28 day strength.

And so CBMs were introduced. These formalise just what the specifier can expect from a 'lean mix' concrete, making it easier to specify the requisite strength for the job in hand. For the project you describe, I'd hazard a guess that you're looking at a CBM4 or 5 because of the chance of vehicle overrun.

I'm not sure about your concerns over the finish of the CBM. A smooth, steel-trowel finish makes for a poorer bond with the bedding layer than would a coarse, open-textured or rough-cast finish. What are you planning to use as the bedding? A mortar? Think about it - bonding a mortar to a smooth, trowelled surface minimises the surface area contact and the degree of interlock compared to bonding a mortar over an open-textured surface, where it will find its way into the voids and interstices, creating a better long-term bond.

Has that shed any light on the matter?

Feb 13th 2003
Cheers that helps a lot.
Forum Question Concrete curing in cold weather - Barry - Feb 16th 2003
I've got some bother with concrete footings.

9 days ago, I took delivery of 4.5 metres of concrete from MixaMate (mixed on-site). 3.5 metres of this was C35 with frostproofer additive and was used to make a retaining wall. The concrete was poured into formwork with reinforcement and, as I expected, has now set like iron.

The remaining 1 metre was C20 (also with frostproofer) and was poured to make footings for some decorative walling. The footings are a little over 300mm wide and around 125-150mm deep on a compacted hardcore bed.

Alas, these footings do not appear to have cured properly. A few days after pouring, I noticed that the top surface could still be scratched with a nail. After 9 days, the surface has "flaked", so that scratching with a nail brings off pieces around 30mm long and a couple of mm deep - almost like a crust. Underneath, it is possible to scratch down about 10mm, and the concrete seems damp and sandy - not at all hard.

Where has it all gone wrong ?! Have MixaMate sold me a pup, or have I done something daft? I've kept the rain off it, and there has only been one frost since pouring (I'm in Croydon). Even so, I did specify frostproofer and I did watch them add a green liquid to the drum...

What can I do now ? Is it possible to abrade the surface and add some compound to accelerate curing and harden the surface ? Or should I rip the whole lot up and start again?

Any advice would be much appreciated.

Thanks - Barry

forum answer Tony McCormack - Feb 146h 2003
The softer material you've found on top of the footing is what we call 'scum'. It's a mix of chemical additives, impurities, and bits of cement, all frothed up during a pour and settling on the surface. Usually, it's no more than 5mm of so thick and can be brushed away, leaving behind a perfectly fine concrete surface.

That the top layer of the actual concrete is iffy is more of a concern, and, from what you describe, it sounds as though the concrete has 'settled' while in place, with the coarse aggregates and cements settling out faster than the sands and fine aggregates. Was a vibrating poker or beam screed used during the placement?

If you're seriously worried, bring back Mix-a-mate (I never did trust those on-site mixings - give me a QSRMC-accredited firm, anyday!) and see what they have to say for themselves.

It's pretty likely that the footings will be sound enough to carry the walls. Given the dimensions you quote, they can only be relatively low decorative walls, and so I wouldn't worry too much. However, if you can push a screwdriver into the surface more than 25mm, then get Mix-a-mate out and ask tham to explain.

Forum Question Concrete base for wooden stables - Susan B - Feb 18th 2003
Hi there,

I am looking into having a concrete base put down for 4 - 6 wooden stables, subject to PP. The size will be something in the region of 25 x 6 metres depending on the layout. The site is level and flat (currently grass), with easy access and reasonably well drained although does suffer in prolonged rain. On another website I have seen an estimate of £25 - £30 per sq. metre for a builder to put down a base of this type. Is this the going rate, does it seem reasonable? I am just trying to get a ball park figure at the moment to see if its worth doing.

Any advice appreciated.
(Greater Manchester area)

TIA - Sue

forum answer Tony McCormack - Feb 19th 2003
That price seems about right, Sue, for laying a 100mm concrete slab in/around the north-west of England. You might even get it a bit cheaper, if you shop around and get in a groundworks specialist rather than a general builder. However, you might also need to consider sub-bases and drainage, which can bump up the price a bit.

Have you been given a spec?

Susan B
Feb 20th 2003
Thanks for your reply Tony,

What sort of spec? Do you mean from the stable manufacturers as to what base they need?

Tony McCormack
Feb 20th 2003
Yes, either from the stable manufacturers or advice from other horse stabling enterprises. The few times we poured yards for stables, we used a high strength (C35) concrete as, apparently, the iron-shod hoofs do a lot of damage to anything 'softer'.
Susan B
Feb 20th 2003
One of the stable manufacturers I am looking at says 100mm concrete on top of 150mm hardcore. It also says that its best to use an agricultural mix of concrete to withstand the effects of acid in the urine. No doubt this will increase the price!
Tony McCormack
Feb 20th 2003
"Agricultural Mix"??? Wossat? I've never heard that term before!

100mm on 150mm of sub-base is the minimum I'd recommend. This 'spec' is illustrated on the Concrete Hardstanding page.

Susan B
Feb 21st 2003
Agricultural mix - a way of adding 25% to the price because it's got something to do with horses!

Thanks for the useful info anyway

I'm emailing you privately about possible contractors

Steve R
Feb 21st 2003
I think the concrete the are refering to is suphate resisting.

We laid our stable floors and yard 15 years ago and with a pressure wash once a year it comes up as new.

Horse widdle is very corrosive, and apparently it attacks ordinay portland cement as well as any metal fittings. It is more expensive but in my experience well worth it.


Susan B
Feb 14th 2003
Thanks Steve - How much more expensive - roughly?
Tony McCormack
Feb 21st 2003
That'll be it, Steve! I was thinking it must be some special additive that I didn't know about, but sometimes, the answer is so blindingly obvious, I overlook it. Sulphate Resistant Cement (often referred to as SRC) is just a few quid per cubic metre extra and is often a standard specification in areas with 'aggressive' groundwater, such as old mining areas. Susan's just outside Manchester, so SRC would normally be specc'ed, anyway.
Forum Question Adding a Pillar to a short wall - madunphy - Feb 19th 2003
Hi all,

I plan to close off open access to my detached house by building side walls (with gates for access). On the narrow side, I have an opening of about 2.1m. The new wall will be butted to an existing brick pillar. My question is the overall length of the wall will be just over 1m, If I add a brick pillar to the other end of the wall, would it make the wall look too short? Should I not bother with the second pillar and just finish the end of the wall with dashing? The other side of the house has room for a second pillar to compliment the original pillar.

Thanks for any advice - Mike

forum answer Tony McCormack - Feb 19th 2003
What size pillars, Mike? 450mm square? Tha'd leave you just 550mm of wall, which, some would say, is a bit of a nothing.

Any chance of getting a photo then we can see it better?

Mar 7th 2003
Hi Tony,

I think it's 450mm. I've uploaded some pictures. The first one is of the narrow side:

mikes wall

You can see were the path and the (future) shed foundation meet, thats were I planned for the wall to finish. Do you think it's too narrow? I've mocked up what it could look like:

mikes wall

Thanks for your help


Tony McCormack
Mar 8th 2003
That's a 450mm pillar (2 bricks wide) and I think it'll look grand, but what about if you infilled between the pillars with a fence panel to match the existing or the proposed gate, rather than use that pebble-dashed finish?

Wodjer fink?

Mar 8th 2003
Hi Tony,

I haven't seen the type of finish (between pillars) you mentioned. Do you think it'll look ok? I'll mock it up (using the neighbour's gates again!!) Would this panel still need a wall behind it?

The reason for the pebble-dash finish came from my neighouring estate that has such a finish and that the house is finished in such a way. Also note that the wider side of the house needs to be closed off and thus my original choice of a walls/pebble finish (we don't want wooden gates as all the neighbours have them). I'd assume that I'd have to use the same finish on both sides for consistancy? Have a look at the pictures I've uploaded. I'll mock up the wide side when I get a chance.

Again, thanks for your time and here's praying to God that we get better weather here this year so that I can get it finished before my wedding in September smile

Cheers - Mike

Tony McCormack
Mar 10th 2003
I suggested the fence-style infill as I thought you were going for that type of gate, but the pebble-dashing looks fine.

You're not obliged to use the same finish on both sides of the wall, though. You could have the pebble-dashing on the outside and have a smooth finish or whatever you fancy on the internal face. It's your wall - have what you want!   smile

What sort of gates will you have? Wrought iron?

Forum Question Shallow services - Diggerman - Feb 21st 2003
Just been excavating my driveway and found the gas, electric, telephone and clean water drains. What a bloody nightmare it was to dig round them. Gas pipe runs down centre of drive and is6" below surface as is electric. Telephone was only 1 brick below ground!! Needed a lot of spade work instead of all mini digger work!! frown
forum answer Tony McCormack - Feb 21st 2003
If you call the gas, lecky and telephone co's, they might be willing to come around and sink those services to a safe depth, at no cost to yourself. It's certainly worth a call.

The drains, I'm afraid, are down to you, and, because of the limitations imposed by manholes elsewhere, you might have to 'live with them', but the gas, lecky and 'phone should be at least 300mm deep. At 150mm depth, they are within the construction layer, which is a bit naughty.

Forum Question Building up levels - B Mackie - Feb 26th 2003
How would I infill an area of about 22m³ which is going to be covered with a concrete drive with retaining walls? Is hardcore ok with 100mm type 1 and 100mm concrete finish?

Any ideas on cheap methods i.e. getting a lorry full of something to infill this gaping hole!!!!!!!!!.

forum answer Tony McCormack - Feb 27th 2003
An area of 22 cubic metres? D'yer mean square metres?

For the fill, you could build up with, say, a SF2 (selected fill) compacted in layers not exceeding 225mm thick, and then top that off with 100mm of DTp 1 or 2, cover that with yer damp proof membrane (visqueen or similar) and then your concrete which needs to be at least 100mm thick. The type of concrete and any reinforcement depends on the use to which this pavement will be put, but, for 22 m², I'd probably use fibre reinforcement rather than mesh steel and rebar.

SF2 is a clean, inert, competent material that is cheap and available locally. Here in The Occupied Former Territories of South Lancashire, it tends to be a crushed Red Bunter/Keuper sandstone, but in North Wales, f'rinstance, it can be a slate waste, and in Cornwallshire it might be quarry waste from the granite industry. In aggregate-poor parts of the nation, such as London and the south-east, it's often a crushed concrete or brick. That's the whole idea behind SFs - they need to be summat cheap and readily available in the local area. smile

B Mackie
Feb 27th 2003
Thanks, but I think it is 22m³ = the length and width are both 6m and the height of the retainer walls are 900mm. Take off 300mm for sub-base and concrete leaving 6.0 x 6.0 x 0.6 =21.6m³ - is this right?

Also why do you put a dpm on drive? Is it to stop concrete settling when its going off?

I know what you mean about compacting and crushed concrete.


Tony McCormack
Feb 27th 2003
So, you've 36 m² in area, and, if you opt for a 100mm concrete slab, that'd be 3.6m³. That leaves 500mm of fill, which is 18m³ or roughly 40 Tonnes.

The dpm goes beneath the concrete, to prevent the mix water be drained from it before hydration has taken place and to protect the concrete from any aggressive ground water once it's cured - see the Concrete page for a fuller explanation.

In hot weather, we sometimes place a temporary dpm over the surface of freshly poured concrete to prevent it drying out too quickly and thereby maintain strength and reduce surface micro-cracking, but that shouldn't be necessary at this time of year.

B Mackie
Feb 28th 2003
Ok cheers thanks for help.
Forum Question Cleaning and Pointing Brickwork - Kevin Oliver - Mar 14th 2003
I have removed my Pebble dash on the front of my terraced house. I was wondering if you had any advice on the best tool for raking-out joints and sanding the brickwork. I have an orbital sander but was wondering whether I should hire a belt sander which might give a better finish. I have a retired bricky linded up to do the repointing so I need to get it prepared. I think the bricks are called London Reds.
Any advice greatfully accepted
forum answer Tony McCormack - Mar 11th 2003
Sanding brickwork??? I hope you've hell of a lot of sandpaper!   wink

The best tool for cleaning up mortar stained brickwork such as you describe is a needle gun, which you should be able to hire from any decent Hire Centre, but be warned, it's slow, tedious, soul-destroying work. frown

For cutting out the joints, you need a nangle grinder. You can now get special 'mortar raking' discs that are around 9mm wide, just wide enough to rake out standard mortar joints in one pass. You'll also need a decent pair of goggle and a dust mask, as cutting out pointing is one of the nastiest jobs in the building trade.

Have you considered asking the pointing brickie to undertake the lot?

Kevin Oliver
Mar 11th 2003
Thanks for this. I hadn't heard of a needle gun before. Is it like sand or water blasting?

The retired bricky won't do anything but the pointing due to his lungs and judging by his cough I think he is right.

He has a mate who may do it so I am waiting for a quote. Hopefully I can get him to do it.

I have an angle grinder so I will try and track down one of these mortar-raking discs.

Tony McCormack
Mar 11th 2003
Needle guns are an air-powered tool that use a bundle of steel 'needles' vibrating at high speed to nibble off any crud from concrete, brickwork, steel etc when preparing them for re-surfacing.

Here's a picture I've scanned in from the Hewden Hire brochure. If you hire from them, I'm sure they won't mind me mis-appropriating their image.....)

needle gun

...and they will also hire or sell the mortar raking discs.

I can't help wondering if your pet Brickie's cough is a result of too many pointing jobs where he's had to do the raking out! wink

Forum Question Compaction rates - Steve Sumner - Mar 14th 2003
I require to know how much type1 and sand do I need to compact to 100mm, for block paving, in mm eg 130mm compacted equals 100mm

Ta for your efforts brilliant site!!


forum answer Tony McCormack - Mar 17th 2003
It doesn't work like that, Steve. Compaction differs between different types of stone, and, while, say, 130mm of gritstone maye consolidate to 100mm, it might be 140mm of limestone or 120mm of granite.

The same goes for sand. 70mm of a Mersey Grit gives around 50mm of compacted bedding, but a quarried sand might need 80mm. And moisture content has an effect on compaction, too.

Only onsite trials will tell you what uncompacted depth you need, but, tonnage can be calculated fairly accurately in advance, if you know the areas involved. The info is given on the sub-base and screeding pages.

Forum Question Avoiding grounding the car - B Mackie - Mar 23rd 2003
I am currently constructing a concrete driveway with retaining walls. The council put in a dropped kerb recently to allow the driveway to be constructed, however when they done this there was a brick wall at the end of the proposed drive so they put the tarmac down to meet existing pavement, and they couldn't put lines up to check the falls etc.

The problem I have is there's a window at the house end of the drive and the customer is stating she doesn't want the retainer wall to be more than 3 foot high. Unfortunately, I think the car will ground out if I lay concrete between the existing tarmac and retainer wall. Are the council reponsible for laying the tarmac to wrong levels, knowing there was driveway to be constructed?

I can't really raise my retaining walls any higher as you would see the whole car when sitting inside the house. Is there a measurement used in constructing driveways to enable builders to know the car will not ground out?

forum answer Tony McCormack - Mar 25th 2003
The 'council' are only obliged to reconstruct the footpath to tie-in with existing walls, edgings, driveways, etc. If they are required to re-lay a section of pavement so that it will tie-in with a proposed driveway or other project, then they need to be instructed, preferably in writing, before they undertake the work, and they would be within their rights to insist that the required levels were set out in advance so that their streetworks team knew exactly what to do. It is not the responsibility of the LA or the Streetwroks Team to set out levels for private developments. They are most unlikely to accept any responsibility for re-laying a path to existing unless it was glaringly clear to them just what levels were required to accommodate the new driveway.

In a word; you're buggered.   frown

To avoid grounding problem, I'm not sure if there is an 'official' recommendation, but the one we always worked to, and I saw it repeated in an article about speed humps in one of the trade publications last week, is that there should be no high point more than 100mm above a flat bone in any 3m run.

B Mackie
Mar 25th 2003
Cheers Tony,

does this mean something like this on the grounding problem...

-----------3m------------3m------------3m----------- the 3m mark it should be no higher than 100mm

Sorry for my drawing, I know its not very good! Would it be possible to give me a diagram to help me understand?


Tony McCormack
Mar 26th 2003
Right, here's the gist of it. In the scenario you've outlined, I've assumed a 1.8m wide typical footpath with 50mm of crossfall. I appreciate it may not be like this, but it will serve as an example. Once you get to the back edge of the footpath, there's a summit point, and the boundary with the private driveway that you're going to construct, which has fall in the opposite direction.

If we take a point on top of the crossing kerb, A, and a point on the driveway 3 metres from A, which is labelled C, and we stretch an imaginary tight line from A to C, then the height of the summit point, B, should not be more than 100mm above that line. In the sketch below, it's shown as 65mm, but that's just the figure that came out in the CAD system, and is meaningless in this example. It might be 50mm or 99mm - it's just a figure.


In the lower drawing this arrangement is shown schematically, with two end points, labelled A and C again, and a summit point, B. The position of the summit point could be anywhere between A and C, but it should not be more than 100mm above the line A-C. I've also sketched in two possible profiles - a hogback curve (in green) and a point-to-point profile (in black). A hog-back curve is always preferable, but not always possible, as can be seen in your project, which is (probably) more like a point-to-point profile.

I've been trying to find my reference for this figure of 100mm over 3metres, but I can't think where it might be. There's nowt in my site notebook, so if I get time tomorrow, I'll check SHW and see if it's in there.

Forum Question Who owns the road kerbs? - Happy Slug - Apr 8th 2003
Outside my house there is a dropped kerb which is damaged.

Who is responsilbe for its repair? The House Owner or Local Authority?

forum answer Tony McCormack - Apr 12th 2003
The Local Authority Highways department, as they 'own' the road, the dropped kerb, and the footpath.

The only exceptions that spring to mind are if the road is unadopted, and therefore not the responsibility of the LA, or if they can show that the damage was caused by a known party, sometimes the householder, or an agent of the householder, such as a builder undertaking work at that address.

Forum Question Childrens' play area - Eddie T - Apr 14th 2003
I am about to landscape an area of approx 8m x 8m to accomodate a wooden playcentre (tower/swings/chute).

The area is presently grassed but lies on a slope with an aprox of difference 1.5m from front to back. The intended top cover will be playbark. I'm not sure how to prepare the ground and what would be the best preparation under the bark.

Any Suggestions?

forum answer Tony McCormack - Apr 12th 2003
The gradient is a problem. 1.5m over 8m is equivalent to 1 in 5-and-a-bit, which is excessive, so some method of reducing that gradient will be required. You could use a retainer at the 'high' end, but the 'drop' such a construction would create will need to be controlled, probably with fencing. If this is a public play area, then you really need to check with your LA as to what they would expect.

As for the bark covering, there are all sorts of regs covering minmum depth of cover depending on the height of the equipment within the play area, but, generally, for any area with a tower or chute, then you'd need at least 300mm of approved bark over a membrane. The ground beneath will need to be cleared of any vegetation, and it's often a good idea to incorporate some method of drainage beneath the membrane to ensure the bark doesn't get saturated and isn't sitting in retained surface water.

If this is your own gardenn, then you can get away with more or less whatecver you want, but if you intend the are to be used by members of the public, such as in a pub playground, then you definitely, absolutely must check the Regulations or you could find yourself in all sorts of bother. SAPCA (see Playground Links Page) would be able to advise.

Eddie T
Apr 15th 2003
Thanks for the reply Tony.

I'm afraid I've misled you with the slope gradient. The drop from front to back over the 8 metres is just under ¾ of a metre. Does this make a difference?

This is area is for my own children and not accessed by the public.

Thanks - EC

Tony McCormack
Apr 16th 2003
Still quite a slope, though, Eddie, but not as bad as I first thought!

Clear the existing vegetation and excavte to formation level, if necessary. Put down a layer of sand about 25-40mm thick and rake it level. Place a membrane such as Terram or similar, and then cover with 200-300mm of play-grade bark, and that's all there is to it. You may well need some form of retainer at the edges, and the bark will need topping up over the next few months, so buy in extra.

Eddie T
Apr 16th 2003
Thanks for the advice Tony!

I am a novice at this!

What would you suggest to retain the edges? Do I need any drainage underneath?


Tony McCormack
Apr 16th 2003
Half-logs are always popular for edging/retaining play bark, or you could use sleepers (new or reclaimed), or a plain timber edging or even a concrete edging kerb, whatever suits your pocket and your taste.

As for drainage, it's essential if what you have is effectively a 'pit' in a clayey patch that will hold water, but, if you're in an elevated spot, then it should be ok. The simplest drainage is to put in a couple of lengths of perforated flexi-pipe and link them to an outfall somewhere, They only need to be laid 100-150mm below the membrane I mentioned, and the typical detail is given on the Land Drain page. In an 8x8m area, I'd do two diagonals and then a link from the centre to the outfall, which could be a point somewhere downhill or an existing drainage system.

Am I going too fast for you, or can you follow my train of thought, so far? Just ask if I'm baffling you with science.   smile

Eddie T
Apr 17th 2003
Thanks again Tony,

I'm a bit hazy on the drainage advice - maybe a diagram would help me (please excuse my ignorance!)

I read another contribution on "flag on edge" - could I use this technique to retain the edges of the play area or would these edges be a potential danger for the kids?


Tony McCormack
Apr 19th 2003
OK, here's a couple of sketches, the first shows a possible construction, using a flag-on-edge as a retainer, if that's what you want to use. There's no problem using it as an edging or retainer, as whatever you use will need to be fairly rigid. Falling an banging your head on a concrete edging hurts just as much as banging it on a timber edging!

play bark

The second image shows a possible layout for a land drain laid beneath the play area.

play area

Does that make it any clearer?
Eddie T
Apr 21st 2003
Thanks again Tony,

Advice and diagrams have been invaluable.

I hope I'll be able to put the advice into practice.

Your site has been a great source of help and advice.

Many thanks - EC

Forum Question Levelling the back garden - Pashfield - Apr 16th 2003
Our garden is relatively flat but has a strip about 5m wide at one edge that falls off by 1m to a hedge. It's too steep to be much use, I'd like to recover this space, ideally bringing it all up to the level of the rest of the garden, then laying it to lawn.

What would be the most cost-effective method of building a structure to enable me to fill it all in? It doesn't have to look special since the hedge will hide it, and it will face away from the house and garden anyway.

Also, what do I use to fill it in - not all topsoil, surely? It will need to be about 25m long, making 62.5m³ of material, if my maths is right. Again, cost-effective suggestions would be welcomed.

Finally, I'd like to thank Tony for a fantastic site - I'm staggered at the quality and quantity of the information on here.

forum answer Tony McCormack - Apr 16th 2003
A flag-on-edge is what you want, even if you didn't know it. They're cheap, a doddle to lay, and damned effective for retainers that won't be seen. Have a look at the Flag-on-Edge page.

To achieve 1 metre of lift, you might be better doing two 500mm lifts, stepped back by, say 450mm or so. Do you know what I mean or do you need a sketch?

Anyway - for backfill, I'd go for whatever cheap fill material was available locally. It might be crushed rock, old hardcore, clay or summat more sinister, but you can use that for the bulk fill, cover it with a membrane, and then put 200-300mm of decent topsoil over the top, if you want to grow summat like a lawn.

25 linear metres at a nominal 4.5m wide and a 1m lift makes 50-odd cubic metres of fill. Reckon on 25m x 4.5m x 0.2m for decent soil, which is 22m³ (40 Tonnes) and that leaves 30 cubes for fill, say 60 tonne. I hope there's plenty of air in your wheelbarrow tyre!   wink

Apr 17th 2003
Thanks Tony, I think I know what you mean.

I like the idea of sinister backfill - I've got a Mother-in-Law that would be a perfect start. Plus, I could get her to do some of the barrowing first   wink

Thanks again, for the response and the site.

The Tool
Apr 21st 2003
Why not try railway sleepers? They are great for this kind of purpose. Lay them on a semi dry mix. I have done that before and to great effect

Previous Page | Main Index | Siteworks Index | Next Page arrow

spacer milonic
Brew Cabin Archive
navigation dhtml
courtesy of Milonic