The caulking in my shower was old and had some mold stains, so I removed it and am planning to re-caulk. After removing the old caulking, I noticed that parts of the removed silicon (the ones removed from the space in the picture) were damp and the sand/grout beneath them was damp. This even though I had not used this shower in about 3 weeks.

I am planning to spray some mold killer in the spaces before resealing. My concern is that the gap is a little big (maybe 3/8 inch), and if I apply silicon directly, water may seep through again over time. Would it be better to put something in the gap first, before applying silicone? Also, how worried should I be about the slight dampness in the gaps?

Thank you very muchenter image description here

2 Answers 2


If it's breaking up there,it's probably breaking up elsewhere. Think about doing the whole shower, it looks like there's more discolored caulk. Stuff some paper towel down in that large space to see if any water remains and to soak up any that's still there. Once you clean it up and spray your mold killer and let it thoroughly dry, get some epoxy grout and fill in the whole seam between the floor and wall. Normal grout wouldn't be used for a change in plane but epoxy grout works well here. It's waterproof and doesn't need to be sealed.


I am not a professional tile person, but after fixing my shower multiple times over the years, I've come up with this observation; silicon caulk will fail eventually and support mold if it's put on thick. And it's also not a good structural material. Unfortunately grout joints at corners also crack over time. Seems like a maintenance job due every several years.

I would clean that mold with bleach and get it good and dry. Then pack and fill all the grout lines with a good grout with a latex admix for water resistance. Then, when dry, give it thin coating of a matching bathroom type silicon caulk. Just enough to seal the joint.

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