Roof and Balcony Waterproofing — Complete Guide

Waterproofing a roof and a balcony together is one of the most common renovation jobs on a home — and one of the most expensive if it isn't done properly. Water getting in through a leaking roof covering or balcony causes follow-on damage of £4,000–40,000 (plaster, timber joists, mould).

Fortunately there is an economical solution that works for both: rubber paint / liquid rubber on an acrylic-latex base. We show you how to waterproof a flat roof and a balcony for the long term in a single weekend.

Why rubber paint for roofs and balconies?

• Waterproof class W3 to EN 1062-3 — the highest classification
• Elastic with over 300 % elongation — bridges cracks and follows thermal movement
• UV-stable A0 — no greying or embrittlement
• Brush straight onto bitumen, concrete, tiles and wood — no primer needed
• Cold-applied — no torch, no fire risk
• Walkable after 24 h, fully loadable after 28 days

Part 1: waterproofing a flat roof

Preparing the surface

1. Pressure washer (max. 120 bar) — remove algae, moss, dust and loose pieces of bitumen
2. Inspect the seams of the old bitumen felt — where cracks are obvious, embed filler or reinforcing fleece
3. Clean junctions with chimneys, roof penetrations and upstands especially carefully
4. Leave to dry (24 h without rain)

Applying in two coats

1. First coat — rubber paint thinned with 5–10 % water, applied with a roller or airless sprayer. Embed polyester fleece (60 g/m²) at junctions, corners and grooves.
2. Leave to dry for 4 hours
3. Second coat — undiluted, at right angles to the first for even coverage

Consumption approx. 300 g/m² in total (2 coats) — up to 400 g/m² on older, porous bitumen roofs.

Part 2: waterproofing a balcony

Balconies usually fall into one of two scenarios:

Scenario A: existing tiles in good condition

Clean the tiles and check the joints — fill them with silicone filler where needed. Then apply two coats of rubber paint directly onto the tiles. The elastic layer absorbs small movements without the tiles having to come up.

Scenario B: screed or concrete base

Fill cracks with sealant, then work polyester fleece into the first coat at the wall junctions. Apply the second coat undiluted.

Optional: a hard-wearing walking surface

For heavy use, a third coat with quartz sand scattered in (grain size 0.1–0.3 mm) gives R10/R11 slip resistance.

What to watch out for on roofs and balconies

• Weather: application temperature +10 °C to +30 °C. Don't start if rain is likely within the first 6 hours.
• Sun: in direct sun above 30 °C the surface skins over too fast — better to work in the morning or on overcast days
• Tools: lambswool roller 12–18 mm or airless sprayer at 15–18 MPa, nozzle 0.019"–0.023". A brush for details and junctions.
• Drying: touch-dry 2 h, rain-resistant 6 h, walkable 24 h, fully loadable 28 days.

Recommended colours for roofs and balconies

• White RAL 9003 — cool-roof effect, reflects sunlight and lowers the indoor temperature
• Graphite / anthracite RAL 7024 — suits modern roof tiles and brick facades
• Black RAL 9005 — the classic replacement for bitumen black
• Grey RAL 7046 — neutral, goes with everything

Consumption and cost

• Carport flat roof (20 m²): approx. 6 kg of rubber paint — one 6 kg tub
• Garage flat roof (40 m²): approx. 12 kg — two 6 kg tubs
• Average balcony (10 m²): approx. 3 kg — one 3.5 kg tub
• Large roof terrace (40 m²): approx. 12 kg — two 6 kg tubs

Conclusion

Waterproofing a roof and balcony with rubber paint / liquid rubber is one of the most economical renovation solutions — cold-applied, no fire risk, in 2 coats and with a service life of 15+ years. For a 30 m² area, the DIY effort is roughly one weekend.

Products and advice: Flat roof guide → · Balcony guide →

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Related terms: Our product is sold in DIY stores and the trade under several names — liquid rubber, liquid rubber paint, liquid membrane, rubber paint, rubberised paint, flexible coating, elastic exterior paint or polymer coating. They all mean the same product: a waterproof, highly elastic coating based on acrylic latex.