Green algae on render / K-Rend? Here's the Linwood Fix
How to tell if it's green render algae
Four tells we look for on every Linwood survey before quoting.
- A green cast on north- or east-facing gables, worst after wet weather
- Pink or orange staining on south walls — that's a different algae but same fix
- Darkening below window sills where water drips
- A textured, slightly rough feel where the render was originally smooth
Why it happens on Linwood properties
North-facing walls that dry slowly stay damp for weeks after rain, and Scotland's ~170 wet days a year keep them within the algae's growth window most of the year.
Splash-back from paved paths and driveways drives spores upward onto the lower 1–2m of render, which is why the greening is often worst just above ground level.
In Linwood specifically, sitting between paisley and johnstone, linwood picks up the same heavy western rainfall — gutter and render maintenance is best done annually here — which is the single biggest reason this issue is more stubborn here than in a drier inland town.
Our Linwood fix — step by step
- 1Test patch
We test a 1m² patch first to confirm no colour lift on your specific render batch — silicone renders vary.
- 2Soft-wash application
Low-pressure application of a render-safe biocide, worked from bottom up to avoid streaking.
- 3Dwell
10–20 minutes contact time depending on staining severity.
- 4Low-pressure rinse
Rinsed at under 500 psi — high pressure damages the render's silicone binder.
- 5Protective biocide film
A residual biocide is left on the surface to slow regrowth for 12–24 months.
What NOT to do
Common mistakes we see on Linwood properties before we're called in.
- Never jet-wash silicone render — it blows the finish off in patches, and re-rendering costs thousands.
- Never use household algae killer diluted from a garden centre — the pH is often wrong and marks the render.
- Do not paint over the algae — it grows straight back through the paint film within 6 months.
Chemistry & materials we use
- Sodium hypochlorite at render-safe dilution (typically 3–5%)
- Non-ionic surfactant so the biocide sheets evenly, no drip marks
- Neutralising rinse compatible with silicone render binders
- No acid-based cleaners — they etch the finish and void manufacturer warranty
Half a day for a typical semi, one full day for a large detached with wrap-around render.
Linwood quote to job completed is usually under two weeks.
£220–£480
£ per typical rendered semi
Every Linwood quote is fixed-price in writing — no on-the-day surprises.
Linwood-specific considerations
Strong belt of 1970s ex-council semis through Brediland and Clippens, plus a wave of modern Persimmon and Stewart Milne new-builds along the Bridge of Weir Road.
Sitting between Paisley and Johnstone, Linwood picks up the same heavy western rainfall — gutter and render maintenance is best done annually here.
On the A761 between Paisley and Johnstone — Linwood jobs are easy to slot into our PA-postcode tight routes. Nearest motorway is the M8, with routes via A761 and A737.
Green Render Algae — questions from Linwood customers
Will run-off harm my planting?+
No — biocide is neutralised on rinse and diluted heavily by the water volume. We still sheet plants where they sit directly under the wash zone.
Is soft-washing safe on my K-Rend?+
Yes — soft-wash is the manufacturer-recommended method for K-Rend and Weber renders. We test a small patch on your Linwood property first and only proceed once we've confirmed no colour lift.
How long before the render greens up again?+
On a north-facing Linwood wall, expect 18–24 months clear with the biocide left in place. South-facing usually stays clear longer.
Do you clean brick and stone as well as render?+
Yes — sandstone, blonde stone and brick all clean well with the same soft-wash chemistry, which matters in Linwood where mixed façades are common on older streets.
Get green render algae sorted this month
Fixed-price quote for green render algae on your Linwood property. Fully insured, Renfrewshire Council-covered, 12-month guarantee on the work.
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