How do you waterproof drywall?

Answer 1

To waterproof plasterboard or drywall wall linings, cover them completely with a waterproof material. Materials that can be used include:

* Acrylic or fibreglass sheet: ~4mm thick stiff solid acrylic/fibreglass sheets that need special jointers and/or sealant at all joins and are glued to the wall lining. Use details provided by the sheet manufacturer. Sealant will need replacing after some years, and can be a mould problem. Sheets require careful cleaning to avoid scratching. Many preformed shower cubicles are made from these materials.

* Pre-coated fibre cement or oil-impregnated wood-based fibreboard: These are also ~4mm thick stiff sheets that need special jointers and/or sealant at all joins and are glued to the wall lining. Use details provided by the sheet manufacturer. Sealant will need replacing after a some years, and can be a mould problem. Sheets require careful cleaning to avoid scratching. * Wall vinyl :~1mm thick vinyl produced specially for wall use. Joints need to be welded to seal and all details must follow the manufacturers instructions. Welding is solvent rather than heat based and these joints are critical so this skilled job best done by experienced tradespeople. Special jointers are available to join wall vinyl to thicker floor vinyl. Cleaning is similar to floor vinyl. * Waterproof membranes with protective covering: Sheets of membranes are lapped and glue or tape sealed. They can be self adhesive or glued on to the substrate. Liquid applied membranes are painted on to the substrate. The liquid applied membranes can be applied to complex shapes. Glass fibre reinforcing is applied between coats, to the joints and corners of substrates to strengthen the membrane. These membranes are then covered it with tile or vinyl as a protective layer as the membranes are not a durable wearing surface.

Note: Glazed ceramic tiles are not waterproof. The glazing is waterproof but the tile is porous. Fully vitrified or porcelain tiles are waterproof, but no grout is truly waterproof, and grout will also get microcracks over time.

Tiling over thick, dense, reinforced cement plaster is a system that has been accepted as water resistant by some because the tiles shed the bulk of the water and the cement resists further water penetration. It is an adaptation from systems used over masonry, where water penetration is not as critical.

Any waterproofing over timber framing must be reliable because any fine cracks or broken seals will admit water to the timber and the rot will not be noticeable until it is well advanced. The substrate for the waterproofing must be as rigid as possible to resist any movement in the flexible timber framing.

Some plasterboard or drywall products are oil-impregnated to resist water penetration. These are not waterproof, and are a backup rather than a waterproofing system.

Some waterproofing systems cannot be used over walls that have a vapour barrier. Check with the supplier.