K-Rend and silicone render cleaning
K-Rend and other silicone renders are the most commonly damaged surface in exterior cleaning, and the damage is permanent. The render is engineered to shed water, so it stays clean longer than cement render — and when algae finally does establish, it sits proud on a surface it cannot soak into and looks far worse than it is. Homeowners then reach for pressure, and the finish is ruined.
The rule for silicone render
Soft wash only. A biocide applied at low pressure, a long dwell, and a gentle rinse. No rotary head. No close-range wand. No hot water at pressure. Silicone render marks permanently under pressure, and the marks are more visible than the algae was — a straight line of clean render with a scoured stripe through it is not something that weathers out.
What we clean this way
- K-Rend and equivalent silicone thin-coat systems
- Through-coloured monocouche render
- Acrylic and polymer-modified renders
- Insulated render systems (EWI), where pressure would also drive water behind the boards
Where the green comes from, and why it starts on one side
North and east elevations stay damp longest, so they green up first. On estate housing laid out in the same orientation, whole rows go at the same time on the same face. It is aspect, not a defect in the render, and it is why treating the shaded elevations properly matters more than doing the sunny ones.
What a proper job includes
- Identification of the render type before quoting — silicone, monocouche and cement render are not the same job.
- Planting and glazing sheeted, beds pre-wetted so anything that carries is diluted on contact.
- Biocide applied at low pressure, worked top-down, with the dwell time the product actually needs.
- Gentle rinse, and the dead growth left to weather off over the following weeks.
- Photo handover, and a 7-day rework window.
What it costs and how long it lasts
Render and wall cleaning starts from £225, with the final figure set by elevation area, access and condition. Expect three to five years before it is due again on an average elevation, less on a permanently shaded north face. A residual biocide after the wash is what moves that number — not how hard the water hit. Full prices.
Frequently asked questions
Will cleaning damage my K-Rend?
Not with a soft wash. It will with a pressure washer or rotary head, and that damage does not come out.
My render is only a few years old — why does it need cleaning?
Silicone render usually needs its first clean between years four and seven. It stays clean longer than cement render, then shows the growth clearly once it establishes.
Can you clean render in winter?
Yes. The biocide works at lower temperatures, more slowly, so the visible result takes longer. Wind and hard frost stop us; cold on its own does not.
Is the biocide safe around planting and pets?
With preparation. We sheet the working line and pre-wet the beds, and we ask you to keep pets indoors while we are applying and until the rinse is finished.
Related
Render & wall cleaning · Soft washing · Why render goes green, black or red · Prices