No seams to fail
Sheet systems leak at laps, joints and details. A liquid system cures into one continuous layer, so the places a flat roof normally fails do not exist on it.
Roofing Solutions / Liquid Roofing
Liquid Applied Roof Waterproofing in London
A cold-applied waterproofing system that cures into one seamless layer over your existing roof. Certified to ETA-23/0735 and installed across South and West London.
Get a liquid roofing surveyWhat liquid roofing actually is
Liquid roofing is a waterproofing system applied to a roof as a liquid, which then cures in place into a single continuous waterproof layer with no seams, laps or joints anywhere in it. It is not a paint and not a coating: it is a reinforced membrane that happens to be formed on the roof rather than rolled out in sheets.
The reason it matters is that it goes on cold, over the covering you already have. There is no torch, no naked flame and no strip-off. We clean the existing surface, prime it, and then apply the system across the field of the roof and up every upstand, outlet and penetration, so the awkward details that fail on a sheet roof are formed as part of the same continuous layer rather than cut, folded and sealed.
It suits any flat or low-pitch roof that leaks but is still structurally sound, which in South and West London means a great many rear extensions, garage roofs, dormers, parapet roofs, commercial blocks and industrial units. K & M Roofing Solutions is a certified applicator of HYDRONYLON, and this page explains what that certification means and, just as importantly, when liquid roofing is the wrong answer.
This page goes deep on one system and assumes you are already looking at a liquid overlay specifically. If you are still weighing it against felt, EPDM or GRP, or you do not yet know whether your roof needs an overlay or a replacement at all, start with our flat roof repair and waterproofing page, which compares all four systems and covers replacement as well.
Benefits
Why a liquid system over a sheet roof
Goes over what is there
The existing covering stays in place, so there is no strip-off, no skip, no disposal cost and no night with the deck open to the weather.
Cold applied
Nothing is heated or torched on the roof, which means no hot works permit, no fire watch and no risk to the building underneath.
Independently certified
The system we apply holds European Technical Assessment ETA-23/0735, which is a published, independently assessed performance record rather than a manufacturer claim.
What we offer
Which roofs it can go over
A liquid system will bond to most existing flat roof surfaces, but each substrate has its own check that has to pass at survey before we commit to an overlay.
Felt and bituminous roofs
The most common overlay we do in London. The check is whether the felt is still bonded to the deck: blistering and lifting laps can be cut, dressed and made good, but a covering that has lost adhesion across the roof has to come off.
See flat roof repair and waterproofingMastic asphalt
Overlays well once cleaned and primed. The check is crazing and thermal movement cracking, particularly along upstands and around outlets, which we cut out and reinforce before the system goes on.
Concrete decks
A good substrate, common on London blocks and parapet roofs. The check is trapped moisture in the slab, because a concrete deck holding water needs to dry or vent before anything seals it in.
GRP and fibreglass
Straightforward once abraded and primed. The check is delamination and star cracking around fixings and corners, which is where a GRP roof usually fails and where the reinforcement has to be built up.
Single ply membranes
Overlays well and avoids stripping a large commercial membrane. The check is compatibility, because some single ply types need a specific primer, and whether the seams and the mechanical fixings are still sound.
Profiled and standing seam metal
Approved for use on metal substrates, and the standard route for an industrial roof leaking at the laps rather than through the sheet. The check is corrosion and fixings, both of which are treated before waterproofing.
See metal roof waterproofingScope
When liquid roofing is the wrong answer
- The deck itself has failed structurally and needs replacing
- Insulation under the covering is saturated and has to come out
- The existing covering has delaminated across the whole roof
- The roof ponds because the falls are wrong and need rebuilding
- A warm roof build-up is required to meet Part L on a refurbishment
- The substrate is contaminated with oil, silicone or loose coatings
- Asbestos-containing sheeting needs licensed removal, not sealing over
- The roof is due for replacement within a year or two anyway
Materials
What ETA-23/0735 certification actually means
Certification is the whole argument for this system, and it is worth understanding rather than taking on trust. Here is what the number means, who issues it and who does what.
What a European Technical Assessment is
The certificateA European Technical Assessment, or ETA, is an independent assessment of how a construction product actually performs, carried out by a designated Technical Assessment Body rather than by the manufacturer. The product is tested against a common European assessment document covering things like watertightness, resistance to wind uplift, behaviour in fire and durability, and the results are published. It matters because it is the difference between a documented, independently verified performance record and a claim printed on a tin.
What ETA-23/0735 covers
The numberETA-23/0735 is the specific European Technical Assessment held by the HYDRONYLON liquid-applied waterproofing system. Quote that number to any surveyor, building control officer or insurer and they can look up exactly what was assessed. If a contractor tells you their liquid system is certified but cannot give you a number, there is nothing to look up.
HYDRONYLON LTD is the manufacturer
Who makes itHYDRONYLON LTD manufactures the system and holds the certification for the product itself. They are also the party that issues the separate 10-year product guarantee on flat roofs finished with it, which is why that guarantee stands independently of whoever installed it.
K & M Roofing Solutions is the certified applicator
Who applies itWe are a certified applicator, trained and approved by the manufacturer to install the system. We do not make it and we do not claim to. That distinction matters because a liquid system is only as good as its application: the certification covers the product, and applicator approval is what confirms the person putting it on the roof was trained to do so and can issue the product guarantee.
How it works
How a liquid roofing job runs
1
Free survey and substrate test
We identify what the existing covering is, check adhesion, look for trapped moisture and test the falls and outlets. This is the visit that decides whether an overlay is honest or not, and it costs nothing.
2
Report and itemised price
You get photographs, a statement of what the substrate is and what condition it is in, and an itemised price separating preparation, detailing and the waterproofing itself. Normally within two to three working days.
3
Cleaning and preparation
The roof is cleaned back to a sound, dry surface, failed areas are cut out and made good, blisters are dressed and outlets cleared. Preparation is the stage that determines whether the finished system lasts.
4
Priming
The correct primer for the substrate is applied, which differs between felt, asphalt, concrete, GRP, single ply and metal. Using the wrong primer is the most common reason a liquid overlay fails early.
5
Detailing and reinforcement
Upstands, outlets, pipe penetrations, corners and laps are reinforced first, because these are where water actually gets in. The field of the roof is the easy part.
6
Waterproofing and guarantee
The system is applied across the whole roof to the specified thickness, inspected once cured, and handed over with our 10-year workmanship guarantee and the separate 10-year HYDRONYLON LTD product guarantee in writing.
Why choose us
Why customers choose K & M Roofing
01
Certified HYDRONYLON applicators, a system most London roofers cannot offer.
02
One team for the whole job, from survey to sign-off.
03
Rated 5.0 by 60 customers on Google.
04
Manufacturer-trained applicators, which is what allows the separate product guarantee to be issued on your roof at all.
05
Transparent pricing with no hidden costs, and a 10-year workmanship guarantee.
Knowledge
Read more before you decide
Common questions
Frequently asked questions
Liquid roofing is a waterproofing system applied to a roof in liquid form, which cures in place into a single continuous membrane with no seams or joints. It is applied cold, usually over the existing covering, and it forms itself around upstands, outlets and pipe penetrations rather than being cut and folded around them. K & M Roofing Solutions installs it on flat and low-pitch roofs across South and West London.
The system is rolled or spread onto a cleaned and primed roof and cures chemically at ambient temperature, with no heat, flame or torch involved at any stage. Reinforcement is embedded into the wet system at details and upstands, so those areas end up thicker and stronger than the flat field of the roof. Because nothing is heated, there is no hot works permit, no fire watch and no risk to the building below, which is why it suits occupied and commercial premises.
ETA-23/0735 is the European Technical Assessment held by the HYDRONYLON system we apply. An ETA is an independent assessment of a construction product carried out by a designated Technical Assessment Body, testing things like watertightness, wind uplift resistance, fire behaviour and durability, and publishing the results. In plain terms it means the product has a documented, independently verified performance record that your surveyor or building control officer can look up by number, rather than a manufacturer claim.
HYDRONYLON LTD manufactures the system and holds the ETA-23/0735 certification for the product. K & M Roofing Solutions is a certified applicator, trained and approved by the manufacturer to install it. We are not the manufacturer and do not present ourselves as one. The distinction matters because the manufacturer issues the separate 10-year product guarantee, and only an approved applicator can have that guarantee issued on a roof they have installed.
In most cases, yes, and that is the main reason to choose it. If the deck is structurally sound, the insulation is dry and the existing covering is still bonded down, we clean, prime and waterproof straight over the top with no strip-off. That removes the skip, the disposal cost and the period with your deck open to the weather. The survey confirms whether your roof qualifies, and we will say plainly if it does not.
Felt and bituminous coverings, mastic asphalt, concrete decks, GRP and fibreglass, single ply membranes, and profiled or standing seam metal, which is approved for use on metal substrates. Each needs its own primer and its own pre-checks: adhesion on felt, crazing on asphalt, trapped moisture in concrete, delamination on GRP, compatibility on single ply and corrosion on metal. Getting the primer wrong for the substrate is the most common cause of an early failure.
When the problem is structural rather than a waterproofing failure. If the deck has rotted or deflected, if the insulation under the covering is saturated, if the existing covering has delaminated across the whole roof, or if the roof ponds because the falls themselves are wrong, sealing over the top just buries the problem. The same applies where a warm roof build-up is needed to meet Part L, or where asbestos sheeting needs licensed removal rather than encapsulation. We would rather tell you that at survey than take the job.
A typical domestic flat roof is one to three days including preparation, and larger commercial roofs are phased in bays so no area is left open. The single biggest variable is preparation: a clean, sound roof goes quickly, while one needing extensive cutting out, blister dressing and detail repair takes longer. Curing times depend on temperature and humidity, and we build that into the programme rather than rushing it.
Two, and they are independent of each other. K & M Roofing Solutions issues a 10-year workmanship guarantee in writing covering our installation, and HYDRONYLON LTD issues a separate 10-year product guarantee covering the system itself. Because the product guarantee comes from the manufacturer rather than from us, it stands regardless of what happens to the installer, which is a meaningful difference from a contractor-only warranty.
Published UK rates for liquid systems run from roughly £40 to £180 per square metre as indicative 2026 market figures, and that spread is worth explaining rather than hiding. It exists because sources lump cheap single-component acrylic coatings in with certified, reinforced systems; the certified end of the market sits towards the top of that range. What moves your figure is the substrate, how much preparation and detailing the roof needs, and access. An overlay still normally costs less than full replacement because strip-off, skip hire and disposal all come out of the job. Those are market figures rather than our quote, and a binding price from K & M Roofing Solutions follows a free survey.
Yes, and this is one of the strongest practical arguments for a liquid system. Everything happens on top of the roof, applied cold, with no strip-out, so there is nothing to clear from the floor below, no hot works permit to raise and far less noise than a strip and re-cover. Offices, shops, apartment blocks and industrial units carry on operating underneath while we work.
It needs dry conditions and a substrate above the manufacturer minimum, so British winter weather is a scheduling constraint rather than a hard stop. We check the surface temperature and the dew point on the day rather than going by the air temperature, because applying to a cold damp deck is how a liquid system fails early. If conditions are not right we stop and come back, which occasionally costs a day and is considerably cheaper than redoing a roof.
Free on-site estimate
Let us talk about your roof
Tell us what is going on and we will arrange a free survey. No pressure, no hard sell, just honest advice and a clear price.
Kamil07593 196505
Mateusz07544 188268