One of the big reasons people choose silicone render is that it stays cleaner than older finishes. But no render stays spotless for ever. North-facing walls, trees, damp corners and city dirt all leave their mark. This guide explains what causes the marks, how to clean silicone render and K-Rend monocouche safely, and how to keep it looking good.
RCR Connections Ltd is Birmingham based, covering the whole of the Midlands. We fit K-Rend monocouche and silicone render, and our team has 62 years of combined experience. We are often asked to look at render that has been damaged by cleaning, not by weather.
Why render gets dirty
Most marks on render are one of these:
- Green algae. Fine green growth, worst on north-facing walls and in shade.
- Black marks. Often mould, lichen or a mix of algae and dirt.
- Streaks under sills and copings. Dirty water running off a sill with no drip.
- Splash marks at the bottom. Soil and grit splashed up by rain.
- White marks. Usually salts or lime bloom, not dirt. See our guide to white salts on render.
- Orange stains. Often rusty beads. See our guide to render beads and stop ends.
Algae and mould need water. If one patch of wall keeps going green, ask why that patch stays wet.
How silicone render stays clean
Silicone render sheds water. Rain beads up and runs off, taking dirt with it, and the surface dries quickly. That gives algae less chance to grow. K-Rend monocouche has silicone in it too, which helps in the same way. But on shaded walls, under trees or where water runs down one spot, growth can still build up over time.
How to clean silicone render safely
- Check the weather. Pick a dry spell, not too hot and not frosty. Most cleaners need a dry day or two after going on.
- Brush off loose dirt. Use a soft brush. Do not scrub hard.
- Use a cleaner made for render. Follow the instructions on dilution and coverage. Test a small, hidden patch first.
- Spray it on evenly. Use a garden sprayer. Cover the whole wall, not just the worst patches, so it cleans evenly.
- Leave it to work. Many cleaners keep working over days or weeks as rain washes the dead growth away.
- Rinse gently if needed. Only if the cleaner says to. Use a hose or very low pressure, from the top down.
Protect plants, ponds, cars and windows from overspray, and wear gloves and eye protection.
What not to do
- Do not use high-pressure washing. It can strip the silicone face, roughen the texture, leave tide marks and push water into cracks and beads. Once the face is damaged, the render gets dirty faster.
- Do not use bleach or strong household cleaners. They can mark coloured render and leave patchy, lighter areas.
- Do not scrub with wire brushes. They scratch the face.
- Do not use acid cleaners without advice. They can etch cement-based render.
- Do not paint over it to hide marks unless you are happy to keep repainting.
Cleaning K-Rend monocouche
K-Rend monocouche is through-coloured, with the colour running right through the render. The same gentle method works: soft brush, a render cleaner, time and gentle rinsing. High pressure is even more risky on monocouche, because it can open up the scraped texture and leave light patches.
Keeping render clean for longer
- Cut back plants and trees. Shade and leaves touching the wall keep it damp.
- Keep gutters clear. Overflowing gutters leave green and black streaks.
- Check sills and copings have drips. Water should fall clear, not run down the face.
- Keep soil and bark below the bellcast bead. That stops splash marks and keeps render off the damp proof course.
- Re-seal around windows when sealant cracks or comes away.
- Look once a year. A spring walk round is enough. Our guide to getting your render ready for spring has a checklist.
When cleaning is not enough
If the render is cracked, hollow, flaking or stained by rust, cleaning will not fix it. Older sand and cement render with flaking paint may be better re-rendered in silicone. Our render repairs page explains what we can repair, and our silicone render page covers the system in full. To see how a whole house is done, read our K-Rend in Birmingham and Solihull page.
Should you get the render cleaned for you?
Ground-floor walls are easy enough to do yourself with a garden sprayer. Upper floors, gable ends and walls over conservatories are harder and need safe access, such as a tower or scaffold. Working off a ladder with a sprayer is not safe on a two-storey house. If the house needs other work, such as new sealant, bead repairs or render repairs, it often makes sense to clean the render at the same time as the access is up.
Cleaning new render
New render should be left alone for the first few months while it cures. If it gets splashed with mud or concrete during the build, let it dry and then brush it off gently. Do not wash new render with chemicals until the maker of the system says it is safe. Some colour change in the first weeks, especially in winter, is just the render drying out and will even up on its own.
A simple care routine
Once a year, walk round the house on a dry day. Look for green patches, streaks, rust stains, cracked sealant and splash marks at the bottom. Clear gutters, trim back plants and check sills. Clean small areas of growth when you first see them, rather than waiting for a whole wall to turn green. That is usually all silicone render needs to stay looking good for many years.
Render looking tired?
WhatsApp me on 07453 614095 or message the page. Send photos of the marks, a wider shot of each side of the house and your postcode.
We work Monday to Friday 7am to 5pm and Saturday 7am to 1pm, and we are closed on Sundays. RCR Connections Ltd is Birmingham based, covering the whole of the Midlands. You can see the towns we cover on our plastering areas and rendering areas pages, and finished jobs on our projects page.
Cleaning silicone render: common questions
How often should silicone render be cleaned?
Many houses only need it every few years. North-facing walls, walls under trees and walls near fields can need it more often.
Can I pressure wash silicone render?
Not at high pressure. It can damage the surface, change the texture and drive water into the wall. Use a render cleaner and a soft brush, then rinse gently if the cleaner needs it.
What are the green and black marks on my render?
Usually algae, lichen or mould. They grow where the surface stays damp, such as north-facing walls, under drips and behind plants.
Will bleach clean render?
It may lift marks for a while, but it can bleach coloured render unevenly and does not stop growth coming back. A cleaner made for render is safer.
How long does a render cleaner take to work?
Some work in a day. Many are sprayed on and left, and the marks fade over a few days to a few weeks as the weather washes them off.
Can silicone render be painted if it looks tired?
It can, with a suitable breathable paint, but it is rarely needed. A proper clean usually brings it back. Painting means you then have to keep repainting.