Balcony waterproofing
with liquid rubber — under tiles or walk-on

Pressure washer (min. 100 bar) — remove old algae, moss, road-salt residue and loose particles. Fill cracks in screed or concrete with elastic repair filler — cracks > 0.5 mm become leak spots later. Renew defective tile joints with sanitary silicone; re-glue any loose tiles first.

For heavily damaged substrate: re-lay the screed and let it cure for at least 28 days — residual moisture must be below 4 % before coating.

Pro tip: Test absorbency with the water-drop test — if water soaks in within 30 seconds, the substrate is ready.

Pre-bend polyester fleece (60 g/m²) into a U-shape: 5 cm on the balcony floor, 10–15 cm up the house wall. Embed into the wet first coat, press flat with a roller — no air bubbles. Also reinforce around drains, skylights and balustrade fixings — these detail points cause 80 % of all leaks.

At the wall-to-floor transition work the fleece carefully into the inside corner — the coating should run up seamlessly.

Pro tip: Pre-condition fleece for 24 h before use — unroll at room temperature so it doesn't shrink back later.

Apply with lambswool roller (short nap, 10 mm) or wide brush. Consumption 100–200 g/m², thin layer in a single pass. Particularly careful on upstands and in corners — these must be sealed without gaps. Press fleece-reinforced spots repeatedly until the fleece is fully saturated and shows through.

Above 25 °C or in direct sun: work before 11 a.m. or after 4 p.m. — otherwise the coat dries too quickly on the surface.

Pro tip: Start on the side opposite the balcony door and work backwards — that way you never walk on a freshly coated area.

At 23 °C and 50 % humidity at least 4 hours, longer in cooler weather (up to 8 h). Test: the coat must no longer be tacky to finger pressure. Protect the balcony from rain and direct sun throughout drying — stretch a tarpaulin over the railing if the weather is uncertain.

The first 24 hours are critical — precipitation can soften the coat and leave water marks.

Pro tip: In high humidity (above 70 %), set up a dehumidifier or apply the next coat the following day — patience delivers the better result.

Apply undiluted, cross to the first coat. Consumption 100–200 g/m². For a slip-resistant finish: sprinkle fine quartz sand (0.3–0.5 mm) evenly into the still-wet coat, let dry for 24 h, sweep off loose grains, then a third thin coat as a sealer. Slip rating reaches R10 (recommended for residential balconies).

Fully load-bearing after 28 days — don't place heavy furniture or planters before then.

Pro tip: Apply quartz sand evenly through a flour sieve, not straight from the bag — otherwise you get clumps and uneven slip resistance.