How a silicone render system works
"Thin coat" is the key phrase. The coloured silicone finish itself is only about as thick as the grains of aggregate in it, often around 1.5mm. That thin layer can't level a wall or bridge cracks on its own, so it sits on top of a system:
- Beads on the corners, around openings and along the base.
- A base coat applied over the prepared wall.
- Reinforcing mesh bedded into the base coat across the whole wall, to spread stress and resist cracking.
- A primer, often tinted to the finish colour, so the base coat doesn't show through.
- The silicone finish, applied by trowel and worked up with a float to bring out the texture.
Skip a layer, or use the wrong base coat for the wall, and the finish will show it, usually as cracking or patchy colour within a few years. The system only performs if it's built as the manufacturer intends.
Why silicone?
The silicone resin in the render makes it strongly water-repellent. Rain beads and runs off the surface instead of soaking in, and a lot of the dirt goes with it. That's why silicone renders tend to stay cleaner than older render types, especially on exposed walls. At the same time, they let water vapour out of the wall, so they don't trap moisture behind them.
Many silicone renders also contain additives to slow down algae growth. They help, but they don't last forever, and shaded, damp walls can still go green in time.
Silicone compared with other renders
| Silicone thin coat | Monocouche | Sand and cement | |
|---|---|---|---|
| Finish thickness | Thin coloured layer over a base coat | One thicker coloured coat | Two coats, then painted |
| Painting | Not needed | Not needed | Needed |
| Water shedding | Very good | Good | Depends on the paint |
| Colour range | Widest | Good | Any paint colour |
| Cost | Usually highest | Middle | Usually lowest |
If you're weighing them up, see our pages on monocouche render and traditional sand and cement render, or our guide to comparing render types.
Colours and textures
Silicone renders come in a very wide range of colours, and usually a choice of grain sizes. A finer grain gives a smoother, more contemporary look; a coarser one has more texture and is more forgiving of slight unevenness in the wall.
Very dark colours need care. Dark render absorbs more heat in sunshine, which puts more stress on the system, and many manufacturers limit how dark a shade they'll allow. If you've got your heart set on charcoal, check it's permitted for the system first. There's more on choosing shades on our coloured render page.
Preparing the wall
Silicone systems can go onto brick, concrete block and sound existing render. Each background needs the right base coat and preparation. Hollow or crumbling render has to come off first, because the thin finish will only ever be as sound as what's under it. Pebbledash usually needs a levelling coat. See our page on covering pebbledash with render.
External wall insulation
Thin-coat renders like silicone are often used as the finish on external wall insulation, where insulation boards are fixed to the outside of the house and rendered over. The Energy Saving Trust explains how solid wall insulation works, including external insulation finished with render. On its own, though, silicone render isn't insulation.
Weather
Silicone systems are sensitive to the weather while they cure. They shouldn't be applied in rain, in frost, or when temperatures are too low for the product, and a fresh finish needs protecting from rain until it has dried. Most rendering is planned for spring to early autumn for that reason.
Looking after silicone render
Silicone render needs less looking after than most. Keep gutters and downpipes working so water isn't pouring down the face of the wall. If a shaded wall picks up algae, a gentle clean, following the manufacturer's guidance, is usually enough. Avoid blasting it with a pressure washer at close range, because the thin finish can be damaged.
Repairs are possible, but like any coloured render, a patch years later won't always match weathered render perfectly. Where a repair would stand out, refinishing the whole elevation from corner to corner often looks better than a patch in the middle of the wall.
Frequently asked questions
Does silicone render need painting?
No. The colour is in the finish, so it doesn't need painting.
Is silicone render the same as monocouche?
No. Silicone is a thin coloured finish over a base coat and mesh. Monocouche is a thicker, single coloured coat that's scraped back.
Why does silicone render stay clean?
The silicone makes the surface water-repellent, so rain runs off and takes much of the dirt with it.
Can silicone render go over existing render?
Often, if the existing render is sound. Hollow or crumbling render has to come off first.
Can I have a dark colour?
Sometimes. Dark colours put more heat stress on the render, so many systems limit how dark you can go.
Are your quotes free?
Yes. Tell us about your house, send a photo of the walls, and we'll come back to you with a free quote.
Interested in silicone render?
Send us a few photos of the house and tell us the look you're after. We'll talk through the system, colours and textures and give you a free quote. For all our exterior work, see our house and wall rendering services.
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