Green Render Algae — What Alexandria Homeowners Need to Know
Most Alexandria enquiries for green render algae follow the same pattern: it looks bad, it's slowly getting worse, and a couple of quick-fix jobs from generalists made no difference. On ex council and 1960s 80s semi stock in Alexandria, the fix is method-specific and the guarantee is only useful if it's underwritten. Here's what we actually do.
How to tell if it's green render algae
Four tells we look for on every Alexandria 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 Alexandria properties
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.
New-build estates share the same render batch across dozens of homes, so once one façade is affected the same streaks appear on neighbours within a season.
In Alexandria specifically, vale of leven catches heavy westerly rain off loch lomond — gutters fill fast and slate moss is the dominant roof issue — which is the single biggest reason this issue is more stubborn here than in a drier inland town.
Our Alexandria 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 Alexandria 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.
Alexandria quote to job completed is usually under two weeks.
£220–£480
£ per typical rendered semi
Every Alexandria quote is fixed-price in writing — no on-the-day surprises.
Alexandria-specific considerations
Heavy ex-council stock through Tullichewan and Bonhill, sandstone terraces in the town centre, and a steady stream of modern Stewart Milne new-builds towards Jamestown.
Vale of Leven catches heavy westerly rain off Loch Lomond — gutters fill fast and slate moss is the dominant roof issue.
Off the A82 — Alexandria work combines naturally with Balloch and Dumbarton stops. Nearest motorway is the A82, with routes via A82 and A811.
Green Render Algae — questions from Alexandria customers
How long before the render greens up again?+
On a north-facing Alexandria 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 Alexandria 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.
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 Alexandria property first and only proceed once we've confirmed no colour lift.
Free quote for Alexandria — same day
Fixed-price quote for green render algae on your Alexandria property. Fully insured, West Dunbartonshire Council-covered, 12-month guarantee on the work.
Related pages for Alexandria
Jump to a specific service, a nearby town, a postcode mini-hub, or an audience-specific package — all fully local to West Dunbartonshire.