The lot owner shouldn’t be renovating a bathroom without a Bylaw in place ( because it’s a major renovation involving CP ) which makes them responsible for the ongoing maintenance re grout, tiles & membranes.
The Fair Trading verdict isn’t applicable in this situation because the fact that the bathroom is being renovated takes precedent. Otherwise it is relevant.
The function of grout is not to prevent water leakage, this is the purpose of a waterproof membrane which is installed underneath the tiles