Basement-wall waterproofing —
against damp & mould

Mechanically remove loose and spalled render — down to sound masonry. Fill out with concrete repair mortar or renovation plaster, let cure for 7 days. The wall must be sound, clean and dust-free before further treatment.

With massive damage (> 5 % of the area) consult a masonry specialist — interior coating alone won't be enough here.

Pro tip: Apply a salt-blocking primer before filling — prevents rising salts from later blasting the repair apart.

Brush salt crystals off dry — never wash, because water only dissolves the salts briefly and they come back. Then apply a salt-blocking primer to stop migration. With mould: use a commercial mould remover, let act for 24 h, rinse thoroughly, dry for 48 h.

Wall moisture must be below 4 % before further treatment — at higher moisture fix the cause first.

Pro tip: Mould is a symptom, not a cause — find the moisture source (condensation, leaky wall, missing drainage) and fix that first, otherwise mould returns.

On strongly absorbent or damp substrate apply a hydrophobising deep primer. This stabilises the render and improves coating adhesion. Let dry for 12 h before further work.

On stable, dry substrate primer can be skipped — proceed directly to Step 4.

Pro tip: In basements with condensation problems, dry with a building dehumidifier for 1–2 weeks before starting — otherwise residual moisture keeps working under the coating.

Work in the first coat generously with brush or lambswool roller — slightly diluted with up to 5 % water for deep penetration. Consumption 150–200 g/m². At settlement cracks or wall-to-floor transitions, embed reinforcement fleece (60 g/m²) into the wet coat and roll flush with a press roller.

Go over corners and connections multiple times — the fleece must be fully saturated.

Pro tip: In damp corners first pull a narrow concrete fillet, then reinforce with fleece — water then runs off instead of collecting in the corner.

After 6–8 h drying apply the second coat undiluted. Consumption 100–150 g/m². Cured and safe against rising damp after 28 days. Until then, ventilate the room with low humidity — a building dehumidifier is recommended.

Against pressurised water (groundwater, hillside) interior coating alone is not enough — additional exterior waterproofing required.

Pro tip: In intensively used basement rooms a third coat is recommended — nearly doubles service life and provides extra reserve against micro-cracks.