Mold under the shower tray?

I have removed the old silicone seal between the tiles and a shower tray. The seal was leaking. There are residues of the material behind the old silicone seal, because the tiles do not go completely under the edge of the shower tray. These residues are also somewhat black, this could be mold.

What can I do to make sure to remove any possible mold in this hard-to-reach area? I cannot remove the shower tray.

Thank you

I would spray a mold remover into the gap, let it dry, and then seal everything with silicone.

I would spray a mold remover into the gap, let it dry, and then seal everything with silicone.

Oh no, definitely not, if the mold is not 100% removed, it will grow back in no time.

What can I do to make sure to remove any possible mold at this hard-to-reach spot? I can’t just remove the shower tray.

If it is properly installed, a sealing tape should be applied between the shower tray and the wall plaster, and the wall should be sealed with liquid membrane (that blue stuff on the wall). The tiles are then not pulled down behind the shower tray but rather the tray is set first (with sealing tape) and then tiled, with the tiles ending just above the shower tray. The gap is then filled with a backing cord and sealed with silicone. First, the cord saves silicone in the gap, and second, it prevents the silicone from adhering to the shower tray, tiles AND wall (3-flank adhesion), which greatly weakens elasticity and causes the silicone to tear quickly.

In your case, it looks like only the tray was set and tiled, and then silicone was pressed in without a backing cord. This is often done. It can be done this way, but it’s just poor quality.

If you want peace of mind in the long term: remove the tray, at least remove the bottom row of tiles, and reset the tray with sealing tape, liquid membrane, then tile again and finish with silicone and backing cord.

Short-term solution as a quick fix: press permanently elastic sealant into the gap from behind, wait, apply backing cord and silicone, and repeat in 5 years.

From an acquaintance who spent many years in Brazil, I heard that to prevent mold, for example in chambers without windows, a light bulb was left on. This produced some heat and convection. My suggestion: Use mold spray and remove mold where accessible. Then seal the tub where water can enter. Leave openings in other places and ensure warmth and convection or draft. This way, the problem should be manageable with little effort.