Build fall into structural members of the balcony to eliminate the need for a sand-cement screed. This will eliminate the need for a central drainage point. Fall to be 1 -100 minimum away from building is best practice. If spitters must be used a minimum of 50mm is recommended (depending on catchment area).
Compressed cement sheet or external grade plywood should only be used (check manufacturers specifications). Particle board (Yellow tongue) is not recommended for external use by manufacturers.
Sheets must be glued and screwed to joists. (Nails will eventually work their way back up.) Where a join in sheets occurs fix a trimmer along the joist to allow appropriate screwing down of sheets (see diagram).
Leave a 4 – 5 mm expansion gap to all joins in sheets.
A step down from the internal floor level is required to allow a vertical rise in the membrane – Stepdowns should be at least 50 mm.
Tiles should be laid with expansion lines over joins in Sheet substrate.
Do not grout wall/substrate junctions of the Balcony! Fill with polyurethane sealant to accommodate expansion. Tiles on balconies can heat to around 60c during hot weather, expansion should be expected.
Flexitray membranes and applications are guaranteed, however, poor construction of the balcony can effect the integrity of the waterproofing and cause failure. These notes are recommendations only, Flexitray would expect builders to research the best possible construction methods applicable to each project.
A problem widespread throughout the industry is that tilers are filling up Leak Control Flanges with screed material or tile adhesive totally rendering the flange useless in its ability to drain water from the tile bed. Water forms a reservoir under the tile bed and constant use sees water travel to any point of exit it may find.
When screeding a tile bed, to a Leak Control Flange, tilers or Builders should place a 100mm pipe off cut or similar into the flange and screed to this. This will keep the flange clear and allow waterproof membrane to be applied down into the flange as per AS 3740.
Builders should educate their tilers exactly on what a Leak Control Flange is designed to achieve to alleviate any costly repairs at a future time.
Install waterstop at extremity of the shower area. The purpose of this is to stop water traveling beneath the tiles to outside the shower area.