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Waterproofing a bathroom, roof, terrace and foundation: what to use and how much to buy
Each zone needs its own material: a flexible coating under bathroom tiles, a liquid membrane for a flat roof or terrace, bitumen primer and mastic for a foundation, tape and spray for joints and quick repairs. Coverage, the order of work and the usual mistakes.
Which material for which zone
There is no universal waterproofing: in a bathroom it works under the tiles and has to stretch with the substrate, on a roof it stays exposed to sun and rain, at a foundation it sits in the ground under water pressure. So decide the zone first, then the material.
Bathroom and WC: a polymer coating such as B. Aquasil, applied by brush or roller, flexible when dry, tiled over. Roof and terrace: the liquid membrane B. Monoflex, a seamless rubber-like layer; white reflects the sun, grey goes under terrace tiles. Foundation, plinth and basement: bitumen primer B. Superbit on the concrete, then mastic or a roll-on membrane. Joints, upstands and parapets: self-adhesive bitumen flashing tape. A pinpoint leak or roof fixings: waterproofing spray.
Bathroom: a coating under the tiles
The substrate must be flat, dry and primed: on concrete and plaster use a deep-penetrating primer or a bonding primer to bind dust and even out absorption. Corners, the floor-to-wall joint and the areas around pipes get waterproofing tape first, because that is where the first crack appears.
Apply the coating in two coats at right angles: the first lengthwise, the second across once the first has dried. Cover the whole floor and run 20–30 cm up the walls, take the shower-zone walls up to 2 m and go 50 cm above the rim around the bath and basin. Tile the next day with a flexible adhesive.
Coverage guide: about 1.5 kg per m² for two coats; the exact figure is on the pack. A 6 kg pail of B. Aquasil covers roughly 4 m², the floor and lower walls of a typical bathroom.
Roof and terrace: liquid membrane
A flat roof, canopy or terrace is coated with the liquid membrane B. Monoflex. It flows over the substrate and dries into one continuous elastic layer with no seams, so it does not leak at overlaps the way roll materials do. White reflects the sun and keeps the roof cooler in summer; grey is less conspicuous and suits tiling or decking on a terrace.
Clean the surface of dust, moss and flaking coatings, open and fill cracks, and reinforce the junctions with parapets and pipes with bitumen tape. Apply two or three coats by roller or brush, each after the previous one has dried, usually 4–6 hours. Work above +5 °C with no rain expected for 24 hours.
Coverage is about 1–1.5 kg per m² per coat. A 13 kg pail does roughly 5–6 m² in two coats, a 5 kg pail about 2 m², and a 1 kg tin repairs one junction or canopy.
Foundation, plinth and basement
The outside of a foundation is first primed with the bitumen primer B. Superbit: it soaks in, binds dust and gives the next layer its grip. Coverage is about 0.3–0.5 kg per m², so an 18 kg pail does 35–50 m². Over the primer go two coats of bitumen mastic or a torch-on membrane.
If the basement is already built and getting damp from inside, use penetrating and cement-based products: the Navitex waterproofer is applied to damp concrete and densifies it. Liquid glass is added to cement mortar (usually 5–10 % of the mixing water) for waterproof render in pits and screeds; neat, it is used to impregnate concrete before other coatings.
A brick or stone plinth and facade are protected with the Aquablock water-repellent primer: it forms no film but makes the surface shed water, so the wall keeps breathing and does not darken in the rain.
Joints, junctions and quick repairs
Most leaks start not on the flat but at the details: a parapet, a pipe, a drain, the edge of a canopy. The self-adhesive bitumen flashing tape EY1280 seals such places in a minute: press the strip onto a dry substrate and run mastic along the edges. The same tape seals profiled-sheet overlaps and gutters.
For spot repairs keep a 700 ml waterproofing spray at hand, clear, white or black. It seals a crack, a joint, screw heads on a roof or the seams of a galvanised sill. It does not replace a membrane; it stops a leak until the planned repair.
The Aquastop impregnation (1 l) protects tile grout, porous stone and balcony concrete from soaking up water. Brush it on; it does not change the colour of the surface.
How much to buy: a quick calculation
Measure the area and add the upstands. A 2 × 2 m bathroom: 4 m² of floor plus 8 m of perimeter × 0.3 m = 2.4 m² of wall, plus about 3 m² in the shower zone, about 9–10 m² in all: two 6 kg pails of B. Aquasil. A 30 m² flat roof in two coats: 60–90 kg of membrane, five to seven 13 kg pails of Monoflex, plus a roll of flashing tape for the junctions. A foundation with 40 m² of outer surface: one 18 kg pail of primer and mastic per the maker's figures.
Everything in this article is in stock at our Tbilisi warehouse: order online, the invoice arrives at once, delivery in Tbilisi the next day and to the regions in 2–3 days. Unsure about coverage? Write in the chat and we will work it out from your dimensions.
Frequently asked questions
Can I tile straight onto the waterproofing?
Yes, a day after the second coat, with a flexible tile adhesive. Do not prime or sand the waterproofing; just check it is dry and no longer tacky.
What is the difference between white and grey Monoflex?
The composition is the same. White reflects the sun and stays cooler, so it is used on open flat roofs. Grey shows dirt less and suits terraces that will be tiled or decked.
Is a primer needed under bitumen mastic?
Yes. Without primer the mastic sits on dusty concrete and peels off over time. Primer soaks in, binds the dust and gives the grip; it uses little, about 0.3–0.5 kg per m².
At what temperature can it be applied?
Coatings and liquid membrane from +5 °C to +30 °C, with no rain for 24 hours and not in direct hot sun. Bitumen tape is rolled onto a dry surface; in the cold warm it slightly with a heat gun.