Exterior Masonry Cleaning in North London Before Painting: Why It Matters

Exterior masonry in North London accumulates pollution, algae, lichen, mould, and carbonation deposits over years of exposure to the urban environment. Painting over contaminated masonry without proper cleaning produces a coating that adheres poorly, fails early, and traps moisture against the substrate. Correct preparation — including professional cleaning — is the foundation of any exterior paint specification.

Pressure Washing

For most exterior masonry, pressure washing with a controlled pressure washer (typically 80–150 bar, lower for soft brick or friable render) removes the majority of loose deposits, algae, and surface pollution. The masonry must be allowed to fully dry (minimum 5–7 days in dry weather, longer in damp conditions) before any paint is applied. We always allow adequate drying time rather than rushing directly from wash to coat.

Biocidal Treatment

For surfaces with algae, lichen, or mould growth, biocidal treatment is applied before or after pressure washing. A proprietary masonry biocide (such as Ronseal Total Care) kills the organisms at their root — surface washing alone leaves viable spores that rapidly re-establish. The biocide requires a dwell time of up to 24 hours before washing off. Our specification includes biocidal treatment on all exterior masonry projects where biological growth is present.

Chemical Cleaning for Specific Stains

Carbon deposits (black staining from exhaust pollution and atmospheric accumulation, very common on North London properties), efflorescence (white salt deposits crystallising through the masonry face), and iron staining all require specialist chemical treatments rather than physical cleaning alone. We carry appropriate treatments in our exterior specification and apply them where required as part of the preparation phase.

Exterior masonry preparation and painting throughout NW3 and North London — call 020 3874 2670 for a survey and quote.