Green Render Algae — What Paisley Homeowners Need to Know
Green algae on render / K-Rend is one of the most common calls we get from Paisley homeowners, and it peaks in spring/summer. Paisley sits 7 miles from Glasgow in Renfrewshire, with the valley holding damp far longer than the map suggests. This page walks through why it happens on PA1/PA2/PA3 properties, how we fix it, and roughly what it costs.
How to tell if it's green render algae
Four tells we look for on every Paisley 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 Paisley properties
Silicone-based renders such as K-Rend, Weber and Parex have a slightly porous face that holds airborne moisture — perfect for green algae (Trentepohlia and Klebsormidium) to establish.
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.
In Paisley specifically, paisley sits in one of the wettest parts of central scotland — rainfall is consistently higher than glasgow city centre, which is why moss and lichen take hold on roofs here faster than almost anywhere we cover — which is the single biggest reason this issue is more stubborn here than in a drier inland town.
Our Paisley 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.
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.
Paisley quote to job completed is usually under two weeks.
£220–£480
£ per typical rendered semi
Every Paisley quote is fixed-price in writing — no on-the-day surprises.
Paisley-specific considerations
Famous Paisley sandstone terraces in the town centre, hillside 1970s estates in Foxbar and Glenburn, and a notable share of bungalows in Ralston and Castlehead — many with original concrete tile roofs now well overdue a soft wash.
Paisley sits in one of the wettest parts of central Scotland — rainfall is consistently higher than Glasgow city centre, which is why moss and lichen take hold on roofs here faster than almost anywhere we cover.
Quick access via the M8 means same-week starts on most Paisley quotes, including the harder-to-park terraces around the town centre. Nearest motorway is the M8, with routes via M8 and A737.
What NOT to do
Common mistakes we see on Paisley 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.
Green Render Algae — questions from Paisley customers
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 Paisley property first and only proceed once we've confirmed no colour lift.
How long before the render greens up again?+
On a north-facing Paisley 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 Paisley where mixed façades are common on older streets.
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.
Book a Paisley render survey
Fixed-price quote for green render algae on your Paisley property. Fully insured, Renfrewshire Council-covered, 12-month guarantee on the work.
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