The insulation boards disappear behind the wall; the render is the part of external wall insulation you will look at every day for the next thirty years. Choosing between silicone, mineral and acrylic thin-coat systems is therefore one of the few EWI decisions that is as much about living with the result as about building physics. Render detail appears on 98 of our real quotes — this guide is the comparison we talk customers through on nearly every EWI survey, including the honest part most installers skip: which choice matters less than you think.
Why the render matters
On an EWI system the render is not decoration — it is the weather skin. The insulation boards behind it (EPS or mineral wool — see the full system breakdown on our external wall insulation service page) have no weather resistance of their own. Everything the British climate throws at the wall — driving rain, frost, UV, the odd football — is handled by a render layer a few millimetres thick.
That skin has to do four jobs at once: keep liquid rain out, let water vapour from inside the wall escape, flex with the thermal movement of an insulated facade (which heats and cools faster than a solid masonry wall, because the masonry behind it no longer soaks up the temperature swings), and look good doing it. The three render families weight those four jobs differently — that is really all the choice comes down to.
How a thin-coat system goes together
Whichever finish you choose, the build-up beneath it is the same and matters more. Over the fixed insulation boards we apply a reinforcing basecoat with an alkali-resistant glass mesh fully embedded in it — this layer, not the topcoat, is what resists cracking and impact. Then a primer matched to the topcoat chemistry, and finally the decorative topcoat itself, typically 1.5–2mm thick, textured as it is floated up.
We install Licata systems, and we use every layer from that one manufacturer — basecoat, mesh, primer, topcoat. Mixing brands to shave pennies voids system warranties and is a classic sign of a price-first installer. An installer's tell worth knowing: ask where the mesh sits. It should be embedded in the outer third of the basecoat with the coat applied in two passes — mesh pushed dry against the boards with render skimmed over it is a corner cut that shows up as pattern cracking a few winters later.
Silicone render: the premium default
Silicone (strictly, silicone-enhanced) topcoats are what we fit most often, and what we recommend when the budget allows. The resin makes the cured render flexible, so it shrugs off the thermal movement of an insulated facade with the least risk of hairline cracking; vapour-permeable, so the wall build-up can dry outwards; and strongly water-repellent — rain beads and sheets off rather than soaking in, which keeps the facade drier and noticeably cleaner over the years, since the dirt and algae that colonise a damp surface get less to hold onto.
It comes coloured through in the widest colour range of the three families, holds that colour well, and needs no painting. The trade-off is simple: it is the most expensive topcoat per square metre. Spread across a whole project the difference is modest — but it is real, and on a tight budget it is a fair place to ask whether you need it.
Mineral render: breathable and fast-setting
Mineral renders are cement-and-lime based, supplied as a bagged dry mix. Their defining strength is breathability — they are the most vapour-open of the three, which makes them the natural partner for mineral-wool EWI where the whole point of the build-up is a vapour-open wall (the logic is the same as in our breathable wall insulation guide). They also set fast, which is a genuine advantage in the short damp working windows of a British spring and autumn.
The trade-offs: cured mineral render is harder and more brittle than resin-based coats, so it depends more heavily on the basecoat and mesh to prevent cracking; and its through-colour range is limited, so it is normally finished with a coat of breathable silicate or silicone paint to get the colour you actually want — which adds a repainting cycle into the facade's long-term maintenance. Mid-priced as a topcoat, with the paint narrowing the gap to silicone.
Acrylic render: the budget through-colour option
Acrylic topcoats use a plastic resin binder. They are the cheapest of the three, tough, flexible and coloured through with vivid, consistent shades — for pure kerb-appeal per pound they are hard to argue with on day one.
The weaknesses show with time. Acrylic is the least vapour-permeable family, so we avoid it over mineral-wool boards and on any wall designed to breathe — over EPS on a modern cavity wall the low permeability matters far less. Its surface chemistry also lacks silicone's water-shedding, so sheltered, shaded elevations green up with algae sooner and want the occasional wash. And strong dark acrylic colours are the most prone to visible UV fading. It is a perfectly serviceable finish in the right place — the right place being a well-drained, reasonably sunny EPS facade and a budget that will not stretch.
Side by side
| Property | Silicone | Mineral | Acrylic |
|---|---|---|---|
| Flexibility / crack resistance | Excellent | Fair — leans on the basecoat | Good |
| Breathability | Good | Best | Poorest |
| Colour range & fade | Widest; holds colour well | Limited; usually painted | Vivid; dark shades fade first |
| Staying clean | Best — sheds water | Good with the right paint | Needs occasional washing |
| Maintenance | Minimal | Repaint during its life | Wash; possible recolour |
| Cost ranking | Highest | Middle | Lowest |
| Best partner | Any board; our default | Mineral wool / breathable walls | EPS on a budget |
On cost: the topcoat choice moves the price of an EWI project by a few percent, not multiples — the boards, scaffolding, labour and detailing dominate. Real project figures are in our 2026 London price report: across 170 priced EWI quotes the median project was £17,300, with finished jobs running £176–£232/m² all-in.
The honest caveat: detailing beats chemistry
Here is the part of the sales conversation most installers leave out: the difference between silicone, mineral and acrylic is smaller than the difference between careful and careless installation of any of them. When a rendered EWI facade fails, it almost never fails in the middle of a flat elevation — it fails at the details. Cracks radiating from window corners where diagonal stress patches were skipped. Water tracking behind the system at a sill with no drip edge. Green staining under a too-short verge. A cracked line at scaffold-lift height where a day's wet edge was managed badly.
Every one of those is a workmanship and design issue that the most expensive topcoat in the catalogue cannot save. It is why render detail — beads, mesh patches, drips, reveals, sills, movement joints — appears on 98 of our quotes as its own scope rather than being buried in a per-m² rate, and why our full EWI guide spends more words on junctions than on boards. Choose the render for how you want the house to look and how the wall needs to breathe; choose the installer for how they treat the details. If you want both priced properly, get a free, fixed, itemised quote — every bead and reveal on its own line.
EWI render FAQs
Which render is best over external wall insulation?
For most homes we recommend a silicone-based thin-coat render: it is flexible enough to resist hairline cracking, vapour-permeable, water-repellent so the facade stays cleaner, and coloured through so scratches don’t show a different colour underneath. It costs more than acrylic or mineral options, but on a finish you will look at for decades the premium per square metre is small. That said, the right answer depends on the wall — mineral render is the better partner for breathable mineral-wool build-ups.
What is a thin-coat render system?
Modern EWI is finished with a system, not a single product: a reinforcing basecoat with alkali-resistant mesh embedded in it, a primer, and then a decorative topcoat only a few millimetres thick — the thin coat. The basecoat and mesh do the structural work of resisting cracking and impact; the topcoat provides texture, colour and weather protection. This is why the finish is only as good as the layers beneath it.
Do coloured renders fade?
All pigmented facades weather over time, but the chemistry matters. Silicone and silicate-based topcoats hold their colour well; acrylic renders in strong, dark shades are the most prone to visible fading in direct sun. Whatever the material, we advise caution with very dark colours on insulated facades — dark surfaces run much hotter in sunshine, which increases thermal stress on the render system itself.
How long does render over EWI last, and what maintenance does it need?
A properly installed thin-coat system should last decades — our EWI carries 10-year manufacturer warranties and a 25-year insurance-backed guarantee. Maintenance is modest: an occasional gentle wash if algae appears on sheltered elevations, and keeping gutters and sills in order so the facade is not streaked by concentrated run-off. Mineral renders may want repainting during their life; silicone and acrylic are coloured through and normally do not.
Which render systems do you install?
We install Licata render systems over EWI — silicone, mineral and acrylic thin-coat finishes as part of their complete system: basecoat, mesh, primer and topcoat from one manufacturer. Using a single-manufacturer system matters because the warranty covers the build-up as a whole, and the layers are formulated to work together. Render detail appears on 98 of our real quotes, so this is a choice we help customers make nearly every week.