New answers tagged crack
If you want to re-try grouting, try with a latex additive in it. Sometimes you need to add it yourself when mixing the mortar. The latex is supposed to add flex to the mortar so changes in space, like between wall, cement board, window etc. due to slight movements from temperature or moisture changes will not cause it to crack. Please note, I only say ...
I had this problem the other day. What you could do to keep it looking nice is fill the cracks in with more grout so that it looks perfect and then put clear caulk over top or dig out all that grout and caulk it with white caulk. There is special caulk that is mildew resistant made specifically for the bathroom.
That should have never been grout, joints between walls and other objects should be caulked because movement in those joints will cause the cracking that you now see, and the cracking can lead to water getting behind the tile. This also goes for inside corners in a shower, and the joint between bottom of the wall and the floor or tub..
The only correct way to fix it, IMHO, is to get some paper drywall tape, and embed it in some setting-type (the powdered kind that you mix with water yourself) compound. Do not use the pre-mixed, and do not use fiberglass drywall tape. In my experience, any other method will eventually open-up on you.
Consider using a paintable latex caulk. Apply a very small amount then work it into the length of the crack with a finger. Wipe off all excess with a damp rag or sponge, then paint. It is a good method requiring no sanding. If your ceiling is painted with flat (no gloss) paint, as most are, you will not be able to see it when you are done.
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