The attached picture is a bathroom floor. The tile worked loose and on lifting it I found extensive black mould under it (killed and cleaned off it before the picture was taken with a mould killer product). The surface under the tiles looks like a thin layer of plywood. The very dark coloured patches in the picture have completely disintegrated to a rotten mush and have clearly been wet for a significant period of time.
To the right of the picture is a shower cubicle which previously leaked (small sealant failure AND a small grout crack) - these leaks have both been fixed. It is likely the source of new moisture has now been stopped.
I believe what has happened is the shower leaked under the tiles, and over time the boarding has rotted in some small places, which has allowed tile movement that has then led to grout failure and a loose tile. It's only at that point I found the mould.
As I see it I have three options:
- Make best attempts to kill the mould (which is almost certainly under the adjacent tiles), dry the area as much as possible, remove and fill the small rotten areas visible, and refit the tile. Downside: Mould may continue to exist and still find a route to emit spores into the living spaces.
- Lift all the adjacent floor tiles (and further if necessary), remove all the damaged boarding, dry the area out and kill any mould, fit new boarding, reinstall the tiles. Downside: Tiles may break when lifted and I have NO spare tiles and probably cannot buy matching.
- Rip the whole floor out and fit new board and new tiles. Downside: Cost, risks of damage to other tiles areas, and extends the area to be re-tiled as ALL tiles of that type need replacing whether affected or not.
The room is on the upper floor of a house (1st floor to us Brits, 2nd floor to my American friends). The floor construction is wooden timbers (likely immediately under the sheet boarding that has rotten) which are left-to-right in the picture, so would probably support movement of water to the affected location. The bathroom is fairly well ventilated with a constantly running humidity sensing fan.
What would you do?