I've got a bad case of grout.
October 13, 2018 10:55 AM   Subscribe

I have cracks showing up in the grout in my shower and I'm looking for advice on how to handle them.

My shower is a one-piece tub with ~12" square tiles on the walls above it. The grout is in generally good condition with the exception of the two corners, where there are cracks running most of the way up and down. Some photos.

I haven't worked with grout before, so I'm looking for advice on how to approach this. The other online advice I've read and watched has been pretty split between a) using a grout knife, removing the cracked grout, and regrouting it, and b) using a filler to fill the crack and calling it good.

Hive mind, what's the right thing to do here?
posted by Special Agent Dale Cooper to Home & Garden (7 answers total) 5 users marked this as a favorite
 
Sanded grout caulk
posted by humboldt32 at 11:02 AM on October 13, 2018 [1 favorite]


If the grout is cracking in the corner then there's a bit of structural movement in the walls, and it's pretty likely that any replacement grout will just crack open again. Also pretty likely that the repeat crack would start letting water seep behind the tiles well before it became visible.

If that were my tiled corner I'd be removing the broken line of grout, spraying the exposed corner with a mould killer, leaving that to dry for several hours (with a radiator shining on it if the weather is cool), then using a fillet of wet-area silicone sealant (the type that includes a fungicide in the formulation) to seal the corner instead of the grout. Cured silicone remains flexible enough to accommodate a bit of wall movement without cracking open.
posted by flabdablet at 11:06 AM on October 13, 2018 [3 favorites]


You should use caulk in corners, not grout. Caulk is flexible.
posted by The Deej at 11:42 AM on October 13, 2018 [5 favorites]


Agreed with the above. Straight grout will crack again, unless somehow that wall movement has been cured. At some point, this problem will necessitate full-depth reconstruction including well-taped and -sealed cement board. In the meantime, filling it with silicone sealant is the best option.
posted by beagle at 11:43 AM on October 13, 2018 [1 favorite]


I have a similar problem in the area around a niche which contains a window. If the corners in the OP's posting are 90 degrees, the corner with which I am concerned is a 270. Is grout caulk still the answer for me? What if I used a grout which is not regular sanded grout?
posted by Nerd of the North at 5:06 PM on October 13, 2018


Grout is really only suitable for filling in gaps between things that will never move relative to one another, like tiles glued to the same wall. If two tiled surfaces meet at an angle, and they're not just different faces of the same solid object such as a brick or concrete wall, then there will almost always be some way for that corner to flex just a little.

Sometimes even a simple concrete wall can cause an inside or outside corner to flex: if you've got tile over sheet cement over concrete, and there's some way for damp to get into the concrete, it can effloresce to an extent that lifts the sheet cement over time.

Timber corners will flex every time the weather changes.

Any amount of flexing will crack grout, so the right thing to use to fill gaps where any amount of movement might occur is a caulk that retains some degree of flexibility. In wet areas like shower stalls or the edges of kitchen sinks, it's important to use a wet-area caulk formulated to include a fungicide because mould grows quite easily on plain silicone.
posted by flabdablet at 8:06 AM on October 14, 2018


Simply caulking over an existing line of cracked grout is also not the best idea. To flex properly, a bead of caulk needs a certain bulk. If you just ram caulk into an existing crack in grout, you end up with a much thinner caulk bead than if you'd removed the cracked grout and replaced it with caulk. The result is quite likely to be that further flexing will strain the thin caulk bead past its elastic limit and pull it away from the cracked grout edge, meaning you'd need to do the whole thing over. Less work in doing it right the first time.
posted by flabdablet at 8:17 AM on October 14, 2018


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