Roof Waterproof per sqm

Waterproofing for slabs (laje) per m²

On flat roofs, terraces, balconies and wet areas, waterproofing a concrete slab (Brazilian Portuguese: laje) is not something you can skip. You size the total quantity with quantity = area_m2 × consumption_kg_per_m2. The pre-formed asphalt blanket (manta asfáltica), reinforced with polyester, weighs about 3 kg/m² and comes in 10 m² rolls. With liquid membranes (Vedacit, Igol, Sika, Denver) you brush or roll on 1.5–2 kg/m² in total, split across 3 coats running in cross directions, and you tuck a polyester reinforcement veil in between the first two coats.

Two Brazilian standards come into play here. ABNT NBR 9575 deals with the design and specification side, meaning the choice of the right system for each use, and ABNT NBR 9574 sets the rules for the work on site: preparing the substrate, a slope of at least 1 %, primer, seam overlaps of ≥ 10 cm, plus a mechanical protection layer. The systems you will run into most are the pre-formed asphalt blanket, EPDM membrane, polyurethane (PUR) liquid membrane, polyurea, acrylic membrane and cementitious crystallizing mortars. For homes, the minimum legal warranty on waterproofing runs to 5 years (CC art. 618), and under the Mário Covas Law / Code of Civil Procedure, botched waterproofing turns up as one of the most common reasons for disputes in incorporations under Law 4.591/64.

Applications

Flat roof slabs (cobertura), balconies and terraces left out in the rain, bathroom and laundry floors, retaining walls (cortinas), planter boxes and pools. Get the quantity right and you steer clear of the familiar mess where an undersized job starts dripping through the bedroom ceiling below by the time the first rainy season arrives.

FAQ

Asphalt blanket or liquid membrane? The blanket lasts longer, around 15–20 years, but you need a torch and someone who knows what they are doing. Liquid membrane is the easier DIY route and works well on tricky shapes with lots of drains, though on exposed slabs it only holds up for 5–10 years.

Do I need to add overlap to the area? Yes. With blankets, tack on 10 % to whatever you measured so the seam overlaps and the turn-ups against the walls (15–20 cm high) are covered.

What is the difference between primer and the waterproofing itself? Primer (imprimação) is a thinned-down asphalt solution that closes off the pores in the concrete and helps the blanket or membrane grip better. On its own it does not keep water out, so the structural waterproofing layer always goes on top of it.