Tank the bugger. It may well be Mrs Jones sunday roast gives off a lot of steam on the windows, which falls as condensation on the sill, soaks in the grout, through to the timber, swells it and lifts the tile. No matter what adhesive you used it'd do it if the timber was subject to moisture. Softwoods moreso than hardwoods.
You could also remove the timber fully with your Fein (or similar) and plasterboard / marine ply it and then prime well or tank it and try again.
Tell Mrs jones she had better tell every friend she has about what a good tiler you are in return for all this mucking around!
You could also remove the timber fully with your Fein (or similar) and plasterboard / marine ply it and then prime well or tank it and try again.
Tell Mrs jones she had better tell every friend she has about what a good tiler you are in return for all this mucking around!
