Sealants for Paving

There definitely are sealants that perform better with one form of paving or another, and there are a worrying number of concoctions that are potential paving despoilers. Sadly, the manufacturers of these snake oils are overly concerned with making empty promises about the panacea their product will deliver and fail to draw attention to the various shortcomings of their infernal compound.

Any attempt to sort the multitude of sealants into appropriate categories would turn into a long and boring chemical analysis. There are polyurethanes (PU), acrylics, 1- and 2-part epoxy resins, fluoropolymers, silanes, siloxanes, waxes and umpteen more. While it may sometimes be possible to identify a most-appropriate chemical type for particular applications (such as PUs for concrete block paving), it is not possible to definitively state that any particular chemical type is best for all pavement surfaces.

Looking beyond the chemistry involved in each class of sealant, all of them can be assigned as either Coatings or Impregnators .

Coatings, also known as Surface Sealants, are those products which merely sit on top of the substrate , acting as a barrier between the paving material itself and the real world. These coatings are, generally, removable. Once applied they can be stripped using a product similar (if not identical) to paint-stripper. Some specialist sealants for other flooring materials may be not removable, but, in general, these are not suitable for use with stone or decorative concrete paving.

These sealants actually penetrate the substrate itself, soaking into the microscopic interstices or capillaries which exist between the individual grains of a sedimentary stone or concrete, or adhering to the surface of mineral grains in other rock types.

We trialled 14 different sealants and colour enhancers on black limestone to see which worked best. Read the results here .

A sealant that is oil repellent is nearly always water repellent as well, but a treatment that is water-repellent is not necessarily oil-repellent.

It's also worth noting that there is a significant difference between repellence and resistance. While a product that is repellent to oil and/or water based contaminants will actively protect the stone from such contaminants, an oil or water resistant product will only slow down or hinder the contaminant to a greater or lesser degree.

Coatings:

• Tend to be relatively inexpensive
• Simple brush-on application
• May impart added slip resistance to some flagstones

Impregnators:

• Longer life-time as the protection is contained within the substrate, and not simply on the surface
• Usually not affected by UV light
• Allow the stone to 'breathe' and so retained moisture can escape

• tend to abrade quite easily, leading to obvious areas of scuffing or wear
• need to be re-applied quite regularly
• can build-up over time to impart a varnish-like appearance to the substrate
• low quality coatings tend to turn nicotine-yellow when exposed to UV light (sunlight)
• can trap moisture in the substrate itself, leading to problems with efflorescence or damage

• tend to be solvent based and may be noxious or harmful to the environment
• care needed when applying to ensure even coverage
• tend to be more expensive than coatings

Finished appearance

• Invisible - Wouldn't know there was a sealant present
• Damp-look – Colours enhanced but not shiny
• Matt/Low sheen - just a hint of shininess
• Wet-look – the full horror; shiny, varnished appearance.

Substrate

• Fairly permeable natural stone (sandstone)
• Barely permeable natural stone (granite, porphyry, basalt, slate)
• Wet cast concrete flagstones
• Pressed concrete flagstones
• Concrete block paving
• Clay pavers
• Plain concrete
• Pattern Imprinted or other Decorative Concrete
• Tarmacadam/bitmac/asphalt
• Resin-bound or resin-bonded

Repellence

• Oil repellent
• Water repellence
• Oil + Water repellence

For residential contractors, reliability, cost and ease of application will be paramount. The primary concern is to provide a reasonable quality sealant for their clients with minimum fuss, risk or hassle. The last thing any good contractor wants is a sealant that causes problems which will involve additional (usually unpaid) work to make good.

There are several different methods of applying sealants. Many of the 'heavier' sealants, such as the Polyurethanes, are best applied using a squeegee, which ensures the whole of the surface is coated but prevents 'pooling' of liquid sealant in low spots. Other sealants may be applied by roller (as in paint roller) or via a sprayer. Less successful (but not impossible) is application by brush (paint brush or soft brush).

The surface to be sealed MUST BE DRY . Moisture on the surface, within the joints or even a bit of damp within the paving itself can cause some sealants to turn 'milky', effectively ruining the finished appearance. Those sealants sold as suitable for all surfaces (the jack-of-all-trades) tend to be more prone to this than some of the higher-end quality products.

Accordingly, we would strongly recommend that sealing should only be undertaken during the warmer, drier months, say May to October. While it is possible to seal at other times, the problem of residual moisture in the paving and relative humidity in the atmosphere can have unpredictable consequences. Further, we would also recommend that a sealant should not be applied until there have been at least three consecutive days of warm (>10°C), dry weather.

Most sealants will require two coats for most effective results. The first coat onto previously untreated paving will often reduce the typical coverage data provided by manufacturers, but second and subsequent coats should see more square metres per litre. There is significant variation in coverage between the various types and brands of sealant, and particularly between different substrates. Very, very rough guidance is given below:

Sealant and Substrate

First Coat

Subsequent Coats

PU sealant on concrete block paving

1-3m² per litre

2-7m² per litre

Impregnator on sandstone

3-5m² per litre

5-15m² per litre

Impregnator on granite/basalt

10-20m² per litre

15-30m² per litre (if required)

Fluoropolymer on most surfaces

3-5m² per litre

Second coat not normally required

The use of stone paving has experienced a massive resurgence over the last decade or so. And not just in the commercial sector: the ready supply of low cost imported flagstones and setts have seen stone increasingly used on residential driveway and patio projects.

Understandably, installers and homeowners have considered using a sealant to enhance and/or protect the new stone paving, and this has resulted in a proliferation of allegedly suitable sealants on the market.

Given the huge variation in types, formats and quality of natural stone now available, compounded by the huge variation in quality of sealants, the section dealing with sealants for stone paving has been moved to a standalone page to allow more detailed examination of the issues.

Read more about Sealants for Stone Paving

One of the most commonly asked questions by email and in The Brew Cabin is to recommend a sealant for a particular project. In fact, it's such a common question that there is now a FAQ to provide what will surely be regarded as a very unsatisfactory answer.

Hopefully, some of the above will have reinforced the idea that, if a sealant is genuinely necessary, then there is no one sealant that can be recommended for every job: all the factors already discussed will have an impact on choosing the most appropriate sealant for each job.

However, it is just about possible to compile a 'shortlist' of the most suitable sealants for a range of substrates and this is given below.

It is strongly recommended that samples of possible sealants are obtained and tested before being applied to larger areas. Contact details for the manufacturers and suppliers of all the products mentioned below can be found on the Sealants Links page.