ETA-23/0735 is the European Technical Assessment number held by the HYDRONYLON liquid-applied waterproofing system, which is the system K & M Roofing Solutions is certified to install across South and West London.
That sentence contains three separate ideas which usually get compressed into one, to the confusion of everybody. This article separates them: what an ETA actually is, what this particular one covers, and the difference between a certified product and a certified installer. If you take one thing away, make it the last of those.
What is a European Technical Assessment?
A European Technical Assessment is an independent evaluation of how a specific construction product performs, carried out by a designated body and published under a reference number.
The mechanism matters. The manufacturer does not carry out the assessment and cannot influence the result. A designated Technical Assessment Body takes the product, tests it against a common European assessment document written for that category of product, and publishes what it achieved. The assessment covers the characteristics that matter for the product’s intended use, which for a roof waterproofing system means things like watertightness, resistance to wind uplift, behaviour in fire, and durability under weathering.
The output is a document with a number. Anyone can ask for it and read what was assessed and what the result was.
That is the whole point. Before certification exists, every manufacturer says their product performs well, and there is no way for a building owner, a surveyor or an insurer to distinguish between the ones that do and the ones that say so. An ETA converts a marketing claim into a published, checkable record.
How is an ETA different from a manufacturer’s own claim?
The difference is who did the testing and whether anyone else can check it.
A technical data sheet is written by the company selling the product. It may be entirely accurate and often is, but it is self-reported and it is not independently verifiable. Phrases like “tested to the highest standards”, “proven performance” and “market-leading durability” appear on data sheets and mean nothing that can be audited.
A declaration of performance is a step up, because it is a formal document, but it still originates with the manufacturer.
An ETA involves a third party with no commercial interest in the result, working to a published assessment method, producing a document that carries a reference number. If a surveyor challenges what is on your roof, “ETA-23/0735” is an answer that survives the challenge. “It is a high-performance waterproof coating” is not.
There is a practical test you can apply to any roofing quote, and it takes one question: what is the certification number of the system you are quoting? A product with certification has a number. A product without it has an adjective.
What does ETA-23/0735 cover specifically?
ETA-23/0735 is the assessment held by the HYDRONYLON system: a liquid-applied waterproofing system, applied cold, which cures into a single continuous waterproof layer with no seams or joints.
The assessment covers the product as a system rather than as a single tin of liquid. That is an important distinction for liquid waterproofing, because performance depends on the whole build-up: the primer for the substrate, the reinforcement embedded at details, the number of coats and the applied thickness. A system certification assesses that specification working together, not one component in isolation.
What it does not cover is your particular roof. No product certification can, because it has never seen your roof. It tells you what the material is capable of when applied correctly to a suitable substrate. Whether your substrate is suitable, and whether the application is correct, are separate questions answered by the survey and by the installer.
For what the system can and cannot be applied over, and the specific check each substrate needs, see our page on liquid applied roof waterproofing.
Who makes it and who applies it?
HYDRONYLON LTD manufactures the system and holds the certification. K & M Roofing Solutions is a certified applicator, trained and approved by them to install it.
These are two different companies doing two different things, and conflating them is the most common piece of misdirection in this corner of the trade.
HYDRONYLON LTD develops and manufactures the product, holds ETA-23/0735 for it, decides the specification it must be applied to, trains and approves applicators, and issues the product guarantee.
K & M Roofing Solutions surveys your roof, decides whether the system is appropriate for it, prepares the substrate, applies the system to the manufacturer specification, and issues a workmanship guarantee for that installation.
We do not manufacture the system and we do not present ourselves as its maker. Any contractor who blurs that line, or who implies that they hold the certification themselves, is telling you something inaccurate about a document you can check.
Why does applicator approval matter more than the certificate?
Because a certified product installed badly is a failed roof, and the certificate does not prevent that.
This is the part worth dwelling on. Certification tells you the material is capable. It says nothing about whether the roof was cleaned back to a sound surface, whether the correct primer was used for that substrate, whether the details and upstands were reinforced before the field of the roof, or whether the system was applied at the specified thickness rather than thinned out to make the material go further.
Every one of those is an installation decision, and every one of them is a common cause of early failure.
That is why manufacturers run applicator approval schemes. They train installers on their specification, and they restrict the product guarantee to roofs installed by someone they trained. A manufacturer will not stand behind an installation carried out by someone whose methods they have never seen, which is entirely reasonable.
The practical consequence for you is the guarantee structure. On a flat roof we finish with HYDRONYLON you receive two documents:
- A 10-year workmanship guarantee from K & M Roofing Solutions, covering our installation.
- A separate 10-year product guarantee from HYDRONYLON LTD, covering the system itself.
They are independent of each other. If something happened to us, the product guarantee would still stand, because it does not come from us. That is a materially different position from a contractor warranty alone, and it is only available because the installation was carried out by an approved applicator.
How do you check an applicator is genuine?
Ask three questions, in writing, before you accept any quote for a liquid roofing system.
- What system are you quoting, by name, and what is its certification number? A named product with a number can be verified. “A liquid membrane system” or “a roof restoration treatment” cannot.
- Are you an approved applicator for that system? Approval comes from the manufacturer. A contractor who holds it will say so plainly and will not mind you checking with the manufacturer.
- Will the manufacturer product guarantee be issued in my name on completion, and can I see a specimen? This is the question that settles it. Only an approved applicator can arrange that guarantee. If the answer is that the guarantee comes from the contractor alone, then whatever is being installed, it is not arriving with manufacturer backing.
Trade guidance also flags some specific warning signs worth knowing: no applicator certification from the manufacturer, vague wording with no named product, and prices under £18 per square metre on a roof more than ten years old. That last figure is a useful sanity check, because at that rate on a roof that old there is not enough money in the job to do the preparation properly.
What should a building owner take from this?
Certification is worth asking about, and applicator approval is worth asking about separately.
The reason this matters commercially is that flat roof waterproofing is difficult for a customer to evaluate. You cannot see the preparation once the system is on, you cannot easily tell a certified reinforced system from a thick acrylic coating by looking at a finished roof, and the failure mode takes several years to appear. In that situation the documentation is the evidence.
A certification number, applicator approval and two separate written guarantees give you something checkable. An assurance that the product is high quality gives you nothing you can act on.
If you want to see how that plays out in practice, our page on flat roof repair and waterproofing sets out how we survey, prepare and apply the system, and exactly what each of the two guarantees covers.