DRAFT v0.1 for review — 28 July 2026 · Highlighted [AUTHOR] markers need Clare's input · Technical sign-off required before publication
Wetpour is usually one line in a much larger project — a small percentage of the capital cost, approved late, under time pressure. But it's the layer every visitor sees, touches and judges, and when it fails, the whole scheme reads as failed. [AUTHOR: a sentence on how surfacing specs typically cross your desk — what state they're usually in.]
The awkward truth is that most of the wetpour failures we're asked to look at were approvable failures: the specification looked complete, said the right-sounding words, and contained nothing that would have caught the problem. Here are the five demands I'd make of any wetpour specification before signing it off — each one is a question you're entitled to ask, and each has a recognisable good answer.
1. A named product from a named manufacturer — not a category
"EPDM" and "TPV" are material families, not products. Within each family, hundreds of producers make granules that differ in polymer content, fillers, pigments, manufacturing process and — critically — how they age. A category name on a spec line is an invitation for the cheapest member of that category to arrive on site.
Demand: the specification names the product, the manufacturer and the place of manufacture, and states that any substitution must be approved against evidence (more on that in Chapter 2 of this series).
A good answer looks like: a specific product name you can trace to a real manufacturer with a real factory — and a supplier comfortable being named.
2. Evidence from aged installations in a comparable climate
Laboratory data predicts; service history proves. Any material with a genuine track record has surfaces in the ground that have been ageing for years, and its manufacturer can tell you where they are, when they were installed, and what they look like now.
Demand: named, dated installations of the proposed material, in a climate and usage comparable to your project — old enough to be meaningful. Five years is a reasonable floor; more is better.
A good answer looks like: "Installed [year], at [place], still in service — here are current photographs, and you're welcome to visit." Vague references to "extensive global experience" without a single dated site are not evidence.
IMAGE — for LinkedIn use images/campaign/evidence-canberra-2017-mustard.jpg + evidence-sydney-2018-red.jpg · suggested caption: “Named. Dated. Photographed against the current swatch card. This is what a good answer looks like.”
3. Test data measured on the finished composite, not the loose granule
Your client's users will never touch a loose granule. They walk on the finished composite — granules, binder and the interface between them, mixed and laid on site. It's the composite that carries load, and the composite that ages. Data quoted for the raw rubber (or for the material as a moulded sheet, before granulation) can flatter a material enormously.
Demand: performance figures measured on the bound, finished system — composite tensile to EN 12230 with the binder type and loading stated, impact attenuation to EN 1177 on the system build-up you're actually specifying.
A good answer looks like: composite results, with the test standard, binder ratio and system thickness stated alongside. If every number on the datasheet is for the granule alone, ask why.
IMAGE — for LinkedIn use images/campaign/diagram-sheet-vs-granule.png · suggested caption: “If every number on the datasheet is for the granule — or the sheet it was moulded from — ask why.”
4. A binder and system matched to the material, colours and climate
The granule is only half the surface. Binder selection determines colour behaviour in sunlight, cure time, weather-window risk during installation, and the long-term bond that holds the surface together. The binder-and-granule combination that's right for one project can be visibly wrong for another — and binder problems tend to show quickly and permanently.
Demand: the specification states the binder type and loading, confirms compatibility with the specified granule (ideally from the same technical source), and reflects the project's climate, colours and site constraints — not a copy-paste from the last job.
A good answer looks like: a granule manufacturer who will talk about binder in the same conversation, and can explain why this binder, at this ratio, for this project. [AUTHOR: optionally, an anonymised example of a binder mismatch you've seen caught — or not caught — at approval stage.]
IMAGE — for LinkedIn use images/campaign/diagram-aliphatic-vs-aromatic.png · suggested caption: “The granule is only half the surface. Binder chemistry decides how the colour behaves in sunlight.”
5. Retained-performance criteria written into the specification
This is the one that separates a handover specification from a longevity specification. If the specification only defines what must be true at practical completion, then everything that happens afterwards is contractually nobody's problem — and the client owns the consequences.
Demand: the specification describes what the surface should still be doing in service: colour stability expectations (with accelerated-weathering evidence such as EN 14836 scores, supported by real aged sites), retained elasticity rather than progressive hardening, granule retention, and continued impact performance.
A good answer looks like: a supplier willing to put year-five behaviour in writing and show you the evidence behind it. Materials genuinely engineered for outdoor service can support this; materials adapted to it tend to go quiet.
IMAGE — for LinkedIn use images/campaign/diagram-uniform-compression.png · suggested caption: “A longevity specification asks what the surface will still be doing — materials engineered for outdoor service can put that in writing.”
The five, on one page
| Demand | The evidence to ask for | |
|---|---|---|
| 1 | Named product and manufacturer | Product identity, manufacturing location, substitution controls |
| 2 | Aged evidence, comparable climate | Named, dated installations; current photos; site visits |
| 3 | Composite test data | EN 12230 composite tensile; EN 1177 on the specified build-up |
| 4 | Matched binder and system | Binder type/loading, compatibility confirmation, climate rationale |
| 5 | Retained-performance criteria | EN 14836 weathering scores; real ageing history; written year-five expectations |
None of these five demands adds cost to a project. Every one of them is uncomfortable only for a material that can't meet it.
Where to go from here. We deliver the full Science of Performance evidence base as a private CPD session for practices and project teams — and if you have a live specification on your desk, we'll review it with you, project-specifically and without charge. Book either at tpv.rosehill.group/science-of-performance.
Clare is [AUTHOR: role/title] at Rosehill Sports & Play, part of Rosehill Group — a UK advanced-materials company manufacturing Rosehill TPV® in Sowerby Bridge, West Yorkshire since [AUTHOR: confirm — TPV production history vs company founding 1988]. She works with architects, landscape architects and local authorities on performance-led surfacing specifications.