We are going to regrout our shower tiles due to some cracks since the technical inspection said it was leaking into the wall which could cause water damage. We removed one soap holder and it seems that there has been leaking water behind it, it was a bit rusty and maybe even molded. Now there are two deep screw holes (see photo). Can we just fill them with grout as well or should it be a different filler? The wall behind is concrete. Do you recommend using a professional for this job or can we just do it ourselves? Worrying a bit for insurance if there is water damage later.
When you re-grout the stall, presumably you will use a mildew remover to get rid of the dark lines that may be left over after the old grout is removed. While using the mildew remover, use a small brush to get the remover deep into the holes of the screws, yes you must have had some leakage there. This must be absolutely clean of mildew and soap scum/residue before grouting or the mildew will grow back out of the grout joints and the screw holes. The soap scum will prevent the grout from sticking the way it needs to as well.
Rinse everything really well. The little bit of water that will get through will be no different that the leaks before. Since this is part of doing a thorough job, this will...hopefully be the last time it gets wet from leakage.
Grout everything, including the screw holes. when wiping down, the grout will recess a tiny bit. Let everything dry for 2 days, check to see if the screw holes are acceptable as they are. If not CAREFULLY, fill and level with caulk. Let dry. If that is acceptable, seal everything with a silicone based tile and grout sealer.
I'd be inclined to either: fit another soap holder; remove the offending tiles and replace; fill the holes with grout, making sure it does more than plug the surface.
With idea 1, put silicone in the holes first, then the screw plug (deeper than the tile, please!) and screw holder on, with a touch of silicone to finish.
With idea 2, there's always a chance you can't get tiles to match, but if yiu can, it's the best option.
With idea 3, putting enough grout to seal the hole won't be difficult, but there will always be two blemishes on the tiles that won't go away.