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Within the first year of living in my apartment, the caulking where the shower stall base meets the wall tiles kept cracking along the entire length of the shower stall like this:

shower stall caulking cracked 1

shower stall caulking cracked 2

The contractor came and fixed it, and I waited 48 hours for the caulking to dry, but it eventually kept cracking. After it being re-caulked three times I finally noticed that when I stand in the shower stall the weight causes the entire shower stall base to bow downward maybe ⅛", which is likely what's causing the caulking to crack. The apartment is no longer under warranty so I'll be addressing this problem myself now.

My questions:

  1. What would the negative effects of water getting between the shower stall base and tiles? Should I be concerned about mold growing in the crevice, water leaking into the apartment below, etc?

  2. How could I caulk this in a way such that it wouldn't be affected by the bowing movement of the shower stall base? For example: should I remove the cracked caulking and then while applying my body weight to the shower stall run a very thick bead of caulk along the edge?

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  • That's nothing, I've seen ABS drain pipe shearing from similar kind of deflection of shower floor. Maybe check if your drain area is properly supported and is not deflecting when you stand there. (it was on second floor and previous owners tried to "fix" it by applying ceiling popcorn patch to the ceiling below...)
    – Eugene
    Jan 25 at 21:15
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    "The apartment is no longer under warranty." In many jurisdictions, you could still file a case against the contractor. Simply because he did not successfully fulfill his warranty duties during warranty time. He just tried many times. It doesn't matter if the warranty time is over - he never successfully removed the mistake(s) he made while he was installing the pan: support beneath the pan seems to be missing and pans/tubs must be filled with weight when caulking, as noted by others.
    – xeeka
    Jan 25 at 23:34

3 Answers 3

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The shower stall has not been installed correctly. The acrylic resin ones do bend when someone steps inside, so the proper way to install them is to put some support below the pan, in the center, to make sure they don't move.

Usually the shower pan comes with feet. If it does not, for example you would lay a few bricks on their side, pour some plaster on top, then set the shower pan on top. Or just plaster if you need less than an inch.

If it is reasonably easy to remove the shower pan, you can remove it and install it properly, with support. That will fix your silicone caulk tearing problem. You can also check if whatever the shower pan lies on is strong enough to support it, or if it is rotten. The problem could come from the shower pan being installed on a support that isn't strong enough and bends, like thin or rotten wood. That's less easy to fix though!

A more "quick and dirty" solution is to make a hole in the side of the pan near the floor and inject a can of expanding foam below it, so the pan is supported from below. If you do that, put some weight in the pan, otherwise the expanding foam will lift it.

enter image description here

Expanding foam isn't as strong as a brick, and it won't fix the floor if the problem is a rotten/bending floor, so this is a "meh" solution, but it is reasonably cheap and much easier to do.

A more temporary solution would be to do a caulking job that doesn't tear. It's not guaranteed to work, but it's better than nothing.

Basically, silicone caulk can stretch by a certain amount before tearing. A larger joint can stretch more before it tears. So the solution is to make a larger joint. First remove the old caulk and grout. If you leave the old rigid grout in, your silicone joint will be thinner, and more prone to tearing. Then apply new caulk and smooth it with a rubber corner smoother like this:

enter image description here

If you don't want it to tear off from the tile, it should be large enough to cover it for at least 2-3mm. Also put some weight in the pan while the silicone cures. You can use a large barrel filled with water, sand bags, whatever.

enter image description here

Since it's a bathroom, you should only use mold-proof silicone. Other types of caulk (urethane, acrylic, etc) are not designed to withstand household cleaning products like bleach.

In any case you have to fix this. If you don't, water will keep leaking out. If the building structure is wood, it will rot. Even if it is a water resistant material like concrete, water seeping out will cause stains and mold on the ceiling in the floor below. Once the building materials are waterlogged, it takes a very long time to dry.

So if you don't fix it today, it would be a good idea to put some tape over the crack right now as a temporary seal.

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  • 2
    Some cheap stuff seems to be made inadequately strong so even if properly levelled and supported it deflects under the weight of an average person
    – Chris H
    Jan 26 at 10:00
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    @ChrisH Yes I've had a nasty surprise with the cheap stuff, that one needed support under the entire pan otherwise it bent like a noodle
    – bobflux
    Jan 26 at 10:11
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    Supporting the shower pan properly is the only long-term correct solution for this. I don't know why people are upvoting answers which suggest only renewing the caulk.
    – RedSonja
    Jan 26 at 12:38
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    Also, while the shower pan is out, get the space under it properly dry before you put it back. If you can, install some form of inspection panel so you can check occasionally if it's damp under there, and dry it again. I speak from sad experience.
    – RedSonja
    Jan 26 at 12:40
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    Fixing the actual cause is the proper answer. More caulk is just applying a band aid to a severed artery.
    – FreeMan
    Jan 26 at 13:05
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  1. You already know the answer to that. Rot, mold, etc. There could be a flange on the shower base that prevents serious issues, though. Have a look.
  2. Your idea of caulking while weight holds the shower pan down is reasonable. That joint is generally not grouted. It should be caulked with something flexible. What we see here certainly isn't.

Some tips:

  • I'd use a urethane caulk for maximum adhesion, or at least pure silicone.
  • Urethane is messy and permanent. Consider masking both sides of the joint with tape. Wear gloves and old clothes.
  • Make sure the area is completely dry first. Put a fan on it for a day.
  • Always use as small a bead as possible. Big, squoozed-out beads look terrible. Here I'd mask, fill the joint, then finger or tool the caulk to flat or a slight cove.
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  • Know with new bathtubs was recommended to fill with water before applying caulking.
    – crip659
    Jan 25 at 21:50
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    @crip659 yes, and if access is tricky remember to use warm water. I ended up sitting in the bath to apply sealant (the shower over the bath was mounted on a false wall nearly a metre long on the long side that wasn't against the real wall)
    – Chris H
    Jan 26 at 9:58
  • One more side effect of the cap is that the water from the shower can get into the plasterboard behind the tiles. If that happens then the plasterboard will swell and you'll get gaps between the grouting and the tiles. Then more water will get in. The damp will also start to spread through the plasterboard along the wall. Eventually the plasterboard will become so sodden that it will start to fall part.
    – Stormcloud
    Jan 26 at 14:01
  • @crip659 can't you just caulk then fill with water? I've always done it that way, then the caulk stretches a bit when drying so it ends up with a more hourglass shape
    – redlude97
    Jan 27 at 0:14
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I thought most shower pans, along with acrylic tubs, have a flange that goes up 1/4 or 1/2 inch from the top of the pan lip. The tile or other wall covering is supposed to overlap that flange so that even if water were to get under the edge of the wall covering, it won't go anywhere. With this arrangement, the caulking is just providing a nice visual look, but is not needed to keep water from getting behind the shower/tub pan.

Look at the illustration from this answer

shower pan attachment to wall

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    While this is (often) correct, I'd still be concerned about the effects of large amounts of water getting into that void over time. Hot water especially as some will evaporate and then condense. Depending on how well things have been put together (and I'm not optimistic here) secondary leaks and wicking are both concerns
    – Chris H
    Jan 26 at 10:07
  • This is a bit like not wearing a seatbelt because you have airbags. Both features help to keep the water out - relying on only one means it's more likely to fail.
    – J...
    Jan 26 at 22:31
  • You can have the airbags without the seatbelt. I'm more than happy with just a 3-point seatbelt (4-point would be my preference) and no airbag.
    – SteveSh
    Jan 26 at 22:34

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