The short answer
Liquid roofing is a waterproof membrane applied as a liquid, usually by roller and brush, which cures on the roof into a continuous, jointless layer. It is based on resins such as polyurethane, acrylic or methyl methacrylate, sometimes with a reinforcing fleece. It suits roofs of awkward shape and can be laid over some sound existing coverings. It is not a cure for a wet, rotten or sagging roof underneath.
How it is applied
The roof is cleaned and any loose or damaged areas are repaired. A primer goes on, because the coating has to bond to what lies beneath. Then the liquid is rolled or brushed onto the surface, with a reinforcing fleece bedded into the wet coat at joints, upstands and penetrations. A second coat and a finishing coat build the thickness, and the whole thing cures in place, joining with itself at every edge.
No flame is involved, which is useful on roofs next to thatch, timber cladding or other fire risks. No stripping is needed in many cases, so dust and noise are low. Because it flows round pipes, corners and rooflights, it is a good way to deal with a roof that has plenty of awkward details.
The resins
Polyurethane coatings are flexible and tough, and they are widely used for general flat roof renewal. Acrylic coatings are cheaper, easy to apply and often used on lower-risk surfaces, but they can soften when water sits on them. Polymethyl methacrylate is a fast-curing resin that sets quickly even in cooler weather, and is chosen where a roof must be back in use soon. Bitumen-based liquids are another option for compatibility with old felt.
Each resin behaves differently, and each manufacturer specifies which surfaces it will bond to. Matching the coating to the existing roof is the first job of a survey, and a failed bond is difficult to see until the coating starts to lift. Our guide to the best flat roof material places liquid systems beside the alternatives.
When it suits a roof
Liquid roofing makes sense on a roof that is dry beneath, with a firm deck, a working fall and a surface that will take a bond. It is often used to extend the life of an ageing but sound felt or asphalt roof, and to seal leaks that start at awkward junctions. It works well on small areas, on repairs round rooflights and chimneys, and on roofs that cannot easily be accessed by a crew with a torch.
Because it is applied over the old surface, it is generally treated as a repair and not a replacement, which can affect whether the insulation has to be upgraded. We explain how in our guide to overlaying a flat roof. Where the work is notifiable, we handle the Building Regulations side.
When it does not
It is the wrong answer for a roof that has wet insulation, soft boards, or long-term ponding. A coating cannot hold up a deck, and it seals moisture in as readily as it keeps it out. Ponding in particular is a problem for acrylics. Cracked or blistered felt that has lifted from its base must be cut out and repaired first, or the defects will telegraph through the new surface. See the page on flat roof blisters for why.
Weather matters at application. The coating needs to go on a dry surface, and rain before it cures can ruin a coat. Warm, settled weather is best, and the cure time between coats is part of the programme. A liquid roof also depends on its thickness. Too thin a coat wears quickly, and the product data states the amounts to be laid per square metre.
Maintenance and recoating
One real advantage of a liquid roof is that it can be renewed. When the topcoat has worn after some years, the surface is cleaned, any damaged areas are patched and a fresh coat goes over the top, without taking the roof apart. Moss and dirt should be washed off from time to time, because a clogged surface holds water and ages faster. Gutters and outlets still need clearing, and no coating removes the need to look at the roof each autumn. Because the membrane is bonded to what is under it, any later repair needs a compatible product, so keep the details of what was used.
Cost and guarantees
Liquid systems are often cheaper than a full strip and replace, because there is no stripping, no disposal and less labour. They are priced per square metre like other coverings, and the range depends on the resin and the thickness. Because costs differ so much from one product and roof to the next, we do not quote a figure here; your fixed quote follows the survey.
Our free survey examines the surface and tests for moisture, and includes photographs of your roof so you can see what we found. If a coating will do the job we say so, and if the roof needs more, we explain what. Whatever route is chosen, the work is covered by written workmanship cover for ten years. The wider range of systems is set out under flat roofing in Basingstoke.
Every roof is different. A free survey with photos settles it for yours.
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