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Apartment building

Mid-rise apartment blocks share one basement, one roof and one set of tanks, so a single leak affects many families. Wet areas stacked above each other make good under-tile waterproofing essential.

Apartment block cut open to show stacked bathrooms, each with an orange waterproofing layer on the floor and up the walls

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Solutions in build order

What this project needs, step by step

Basement wall and base slab of waterproofed concrete holding back ground water, with a waterstop in the wall-slab joint Waterproof (watertight) concrete For basements, water tanks, pools and sewage works, make the concrete itself resist water with a low water–cement ratio, an integral waterproofing admixture and sealed construction joints. This is for new pours; it cannot fix a structure that already leaks. 7 steps Basement section with a membrane on the outside face of the wall and under the floor slab, facing the groundwater. Basement waterproofing from outside (positive side) For new basements, or where the soil can be dug away, stop water on the face that the soil and groundwater press against. Build watertight concrete, seal every joint, coat or sheet the outside face, then backfill carefully. 7 steps Lift pit section below the floor, lined inside with a waterproof coat, with guide rails and a buffer spring. Lift pits and drainage sumps Lift pits and drainage or sewage sumps are the lowest points in a building, so groundwater collects there. Build them watertight, seal the kicker joint, and line them with a slurry rated for water pressure. 6 steps Section of an underground concrete water tank in wet soil, lined on the inside, with joint waterbars and a sealed pipe Underground water tank Below-ground tanks leak out when full and let groundwater or dirty water seep in when empty. Plug and repair, then line the inside with a drinking-water coating; on new tanks, build watertight concrete and joints first. 7 steps Section of a bathroom floor with waterproofing turned up the walls under the tiles, sloping to a floor drain Bathroom waterproofing (under tiles) Most home leaks start in bathrooms: water gets through grout and cracks, runs along the slab and shows as seelan on the ceiling below or the wall next door. Strip, seal cracks, waterproof the floor and lower walls, then tile, grout and seal the fittings. 6 steps Section of a walk-in shower with full-height waterproofing behind the tiles, sealed pipes, a drain and a glass screen Shower area & walk-in shower The shower is the wettest spot in the house: floor, walls, niche and drain are soaked every day. It needs a continuous waterproof layer from floor to wall, epoxy grout and a mildew-resistant sealant at every corner. 6 steps Floor tiles on an orange adhesive bed over screed and slab, with sealed movement joints and a notched trowel above Floor tiling (homes, shops and outdoor floors) Fixing ceramic, porcelain and stone floor tiles indoors, on courtyards and terraces, on heated floors and in shops with heavy foot traffic. A flat, mature base and the right adhesive stop hollow, cracking and lifting tiles. 7 steps Close-up of floor tiles with joints filled with orange sandy grout and a rubber grout float above Cement tile grout (everyday floors and walls) Coloured cement grout for ceramic, porcelain, marble, granite and mosaic joints, on floors and walls, inside and outside. In wet areas it is mixed with a latex instead of water. 6 steps Flat roof section with an exposed coating on the slab, turned up and over the parapets and into the drain outlet. Exposed roof waterproofing A liquid-applied membrane that stays open to sun and rain on a flat or sloped concrete roof (chhat). Use it on a new roof once the slab is 28 days old, or to refurbish a leaking roof before the monsoon. 6 steps Balcony section with a waterproof coat under the screed and tiles, turned up the wall, and a railing post. Terrace and balcony waterproofing Balconies, terraces and open verandas that people walk on, usually finished with tiles. The waterproofing goes under the tile bed and turns up at walls, door thresholds and drains. 6 steps Section of a rooftop concrete water tank full of water, lined on all inside faces, with sealed pipe entries Overhead water tank (drinking water) Rooftop RCC tanks that leak, wet the ceiling below or show rust stains. Repair the concrete first, then line the inside only with products whose data sheet allows drinking-water contact. 6 steps Two concrete slabs on columns with a gap between them sealed with orange sealant over a round foam rod Building expansion and movement joints The gaps between building blocks, slabs, walls and roofs that let the structure expand, shrink and settle. They need a sealant or tape matched to the movement, a correctly sized joint and a backer rod, or water gets in and edges break. 7 steps Window in a brick wall with an orange sealant bead round the frame, and a close-up of the frame-to-wall joint Window and door frame sealing Sealing the gap between aluminium, uPVC, steel or timber frames and the wall, plus glass-to-frame and interior finishing joints. This is a common place for monsoon rain to get into a home. 6 steps