Cold-Applied Liquid Waterproofing & Detailing

Systems

Where liquid earns its place

Most flat roof leaks start at details, because details are where sheet membranes have to be cut, folded and lapped. A liquid system has no laps: it is applied wet, reinforced at stress points, and cures as a single unbroken skin over whatever shape it meets. We specify it across South London where that property matters most:

• Upstands, kerbs and edge details
• Pipe and cable penetrations, vents and plant bases
• Complex junctions where several planes meet
• Anywhere an open flame is ruled out
• Full-roof overlays, where an inspection supports one

Full-roof overlays, not only detailing

The last item on that list is the one people underestimate. A liquid system can take the whole field of a roof, not just its details, which makes it a refurbishment route in its own right: no tear-off skip, no exposed deck, and one continuous membrane from parapet to outlet.

It is also the overlay we put forward first, for reasons that survive being questioned. Laying fresh sheet over a tired roof loads the building with a covering it did not have before and introduces a fresh set of joints into it. This arrives as one cured piece, at a fraction of that weight, and no flame goes anywhere near the detail. First is not always, though: a felt overlay gets specified where a particular building asks for one, and the quotation explains it. Which roofs qualify for either is set out in the refurbishment options guide; what an inspection has to find underneath first is the subject of repair or replace. Once an overlay is agreed, the days on site are walked through in a liquid overlay, step by step.

Fire safety

Where a flame should not go

Where a roof is being laid new, liquid waterproofing works alongside torch-on felt rather than instead of it. The field of the roof gets the robustness of a torch-on built-up system; the details near timber cladding, eaves boxes and other combustible construction get a cold-applied finish that needs no flame at all. That follows the NFRC's Safe2Torch guidance: the fire risk is assessed before a torch is lit, and a cold-applied system goes wherever a flame should not. Each material does the job it is best at.

Credentials

Named in the specification, with published credentials behind it

Plenty of roofing quotations say "liquid system" and stop there, which leaves you unable to check anything. Ours says HYDRONYLON, along with the build-up, the reinforcement and the preparation, before a tin is opened. A named system is a system you can look up, and the credentials it publishes are these:

• Assessed under European Technical Assessment ETA-23/0735, the European route by which a waterproofing system is independently examined against a defined standard.
• A working life category of W3 under that assessment, which is defined as 25 years. That is an assessment of durability reached by testing, and the document states in terms that it is not a promise from the producer.
• An external fire performance classification of B(roof)(t1), and a reaction to fire classification of Class E.
• A product guarantee of 10 years from completion, issued to Approved Contractors by the system's British distributor on the terms it publishes. Its length is set by that distributor and not by the assessment above, which is why the two figures differ.
• Pluvian Roofing Ltd is a HYDRONYLON Approved Contractor, certificate HAC-0007, valid to September 2028 and confirmable with the distributor that issued it. The certificate is what lets the system be named in a specification and laid under the terms of that approval. It is listed with its dates on our contractor information page, as everything of the kind will be. What installing under it involves is set out on the approved installer page.

Source: European Technical Assessment ETA-23/0735, version 2, issued 17 July 2026 by the Łukasiewicz Warsaw Institute of Technology for Proof-Tech Sp. z o.o., Gliwice.

Those are the system's credentials, not ours. The ETA belongs to the manufacturer, and the approval and the product guarantee to the system's British distributor, whose documents you can read on the system's own site. What we bring is the inspection that decides whether it suits your roof, the specification that pins down how it goes on, and the workmanship that makes any published figure mean something.

Guarantees

Who guarantees what, and what you actually receive

Guarantees in this trade are usually explained badly, so here is the whole arrangement. There are two of them and you are given one.

The product guarantee depends on the roof being kept up to the system's instructions, which is why we offer planned maintenance.

So you end up with one document, from us, covering the work, and behind it stands the product guarantee we hold as an Approved Contractor. That is why the certificate matters to you rather than to our letterhead: without it there is no second layer for ours to stand on.

The distributor's layer is conditional on the roof being maintained in line with the system's instructions, and it excludes damage that reasonable inspection would have prevented. Meeting that condition is what a maintenance programme is for, and that page carries what a visit includes rather than this one selling it.

Substrates

The surfaces the assessment names, and the ones it does not

A liquid system is only as good as its grip on whatever is already up there, so the assessment behind it names the surfaces it has been examined on and specifies a different base layer for each: felt and built-up bitumen, metal, mineral surfaces such as concrete and screed, and PVC membrane. Those are the documented cases, and where your roof is one of them the specification simply says which base layer applies.

Roofs are less tidy than assessments. Surfaces turn up that sit outside that list, and two things are then true at once: we do genuinely work on some of them, and the assessment does not cover them. So neither claim gets made here. What happens instead is that the surface is identified, prepared as the system requires and put through an adhesion test on the roof itself, and the answer comes from that test rather than from this page.

And where a substrate falls outside the assessment, what any guarantee covers is set down in the quotation itself, before anybody starts. The paperwork behind a roof matters as much as the roof: a surface nobody documented is a conversation nobody wants to be having in five years.

In practice that list maps onto four kinds of job. Over felt it is the alternative to a second sheet covering, and over a profiled metal roof it is how laps and fasteners stop being individual leaks. On mineral surfaces it is what makes sealing existing balconies and terraces possible at all, because those decks are mostly threshold, upstand and outlet and a sheet has to be cut around every one of them. On single ply only PVC is named, which is why TPO and EPDM are tested on the roof and never promised from a page. What sits outside the list entirely, including mastic asphalt, is judged the same careful way.

An overlay is the whole system, over an existing base

An overlay is the complete specification applied over the covering already there: the base layer matched to that surface, the reinforcement embedded in it, the top coat over that. Nothing is left out to make it cheaper. What separates it from a new roof is not the system, it is what sits underneath.

An overlay buys a new waterproofing layer on an existing base, and that base keeps its age, its falls and its history. Replacing the covering resets the build-up underneath as well. So the two are inspected and priced as different propositions, and that is where an overlay earns its place: it adds years to a roof for a fraction of what stripping and rebuilding one costs.

What sits under the new layer is what decides between them, and that was always the real test rather than a comparison of published lifespans. Where the boarding has softened, the falls have gone or the insulation is wet, the honest answer is usually a new roof, and saying so is the point of inspecting first rather than putting a fresh layer on a roof that has run out of road. Where the deck is sound and the falls still work, the overlay is the better spend by a distance. The inspection says which, and the quotation carries the reasoning.

Weather

What the weather has to be doing

Cold-applied means no flame. It does not mean the material is indifferent to the conditions, and this is the part of liquid work that most quotations leave out. The system cures chemically, and it needs the surface dry, the humidity within limits, and the temperature held inside its working band right through the cure, overnight included, not just while somebody is on the roof at midday. Where a build-up takes more than one coat, a full day between coats is part of the programme rather than a delay in it.

What that means in practice is that a cold snap or a wet spell moves the work, and we would sooner flag it while the date is being agreed than after a crew has arrived and stood down. It also means the choice of system is sometimes a question of the calendar: torch-on felt is what gets specified where a roof must be made watertight in weather liquid will not cure in, and on a roof that needs both, the sequence is planned around it.