Wet Areas & Mould
When waterproofing a wet area, it is worthwhile considering how best to create a safe environment for the occupants. Many homes within Australia use a mortar based screeded bed to achieve falls to the drainage outlets & have the waterproofing under the screed, especially within the shower area.
Water doesn’t take long to find a hairline crack from thermal movement or building movement within the tiled wet area grout and seep into a dry mortar-based screed below the tiling.
This itself is not such an issue, as mortar-based screeded tile beds, still are fit for purpose if they are wet or dry.
Australian Standards AS3740-2010 amendment 2012 for internal wet areas, deals with water seepage through the grout and screeded tile bed.
It is important to note that a drainage flange is compulsory in all wet areas
(not a riser cut off), the waterproof membrane terminates into the drainage flange. The advantage of the drainage flange allows the natural air flow over the waste outlet creating a wicking effect of the screeded bed, thus drawing the moisture out of the tile screeded bed and reducing the tile screeded bed saturation.
Waterproofing on top of a screed bed, with direct sticking the tiles, will minimise the risk of fungi/mould in the screed bed while still maintaining a fit for purpose wet area.