Masonry Water-Repellent Coatings

Brick and block walls absorb rain. That is normal, and most walls dry out again. Problems start when the wall stays wet: damp patches inside, efflorescence on the surface, spalling render, and eventually decay of the mortar and the masonry itself.

A water-repellent coating — usually a silane or siloxane — lines the pores of the masonry so water beads off while the wall continues to breathe. That breathability matters: a film-forming paint or sealer that traps moisture can cause more damage than it prevents, particularly on a wall that is wet from behind.

Preparation is essential. The wall has to be clean, sound, and free of failed paint, loose render and salts. Cracks and open joints are repaired first, because a repellent will not bridge a crack. A test panel tells us how much the masonry absorbs and how the product performs before we treat the whole elevation.

A repellent is not a cure for rising damp or for water coming through a failed roof or gutter. If the source is below or above the wall, coating the face will not stop it — the source has to be dealt with first. We diagnose the path of the water before recommending a treatment.

Repellents also have a service life. On an exposed elevation, reapplication is usually needed after a number of years, depending on the product and the exposure. We say what to expect and how to check whether the treatment is still working.