Plank shower with marble benchI get quite a few questions here concerning cracking grout on a shower bench. In some form or another people are mostly asking whether they should caulk or grout the outside corner, where the bench top meets the vertical tile on the face. The reason for asking me this, however, is what I will address in this post.

Most people begin with something like ‘my grout has cracked and now water is getting behind my tile and my bench is starting to swell, there was an eclipse, my dog has burst into flames…it’s a whole thing. Should I grout or caulk that?’

Unfortunately this happens a lot (the bench, not the eclipse or k-9 flames…), and everyone thinks about it backwards. It is not the grout (or missing grout) that caused water to leak into your bench and swell the framing, it was the swelling of the framing that caused your grout to crack. Tile and grout are not waterproof. The reason you have this issue is because your bench was not properly waterproofed before tile was installed.

Water will get behind your tile and grout, it’s completely normal. If your shower is properly waterproofed there will be no issues. If it is not waterproofed correctly the water will get into your framing and begin to make it swell. Once that happens it will cause grout to crack (the first sign), tiles may become unbonded or crack as well. Before you know it the sun disappears and your dog is your only source of light.

So if you have cracking grout on your bench you need to remove and rebuild your bench – because it is not properly waterproofed. I describe the process in my post about (…wait for it…wait for it…) How to build a shower bench!

If you have any questions feel free to leave them below, I answer them every day when I sober up get off work. I will, however, head off some of the most common:

No, there is no magic product, not even silicone, that you can put over your cracking grout line to miraculously make it waterproof again. It never was waterproof.

Yes, if your bench grout is cracking you NEED to replace the bench, or at least remove all the tile, see what sort of substrate you have to work with, and properly waterproof it. You can normally use a topical membrane of some sort over your existing substrate to fix it. But you DO need to remove all the tile on the bench to do this.

If you do have a barrier behind your wall substrate there is no way to tie in the waterproofing on the bench to the waterproofing on the wall. However, utilizing a topical waterproofing membrane on your bench will still be better than whatever you may currently have under there.

So that’s it, if you have cracking grout on your bench it is because your framing is swelling, your framing is not swelling because you have missing grout. This also applies to most any missing grout in a shower – especially curbs. Water WILL get behind your tile – it’s normal. If your shower is properly waterproofed it is not an issue. If you need to learn how to properly waterproof a shower just click on the library tab at the top.  If you have any questions at all just leave them below.

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  • Virginia Fox

    We had our garden tub removed and replaced with a porcelain tile shower. Two weeks into using the shower, mildew appeared on shower floor. The tile man said he had applied sealer to the grout lines to prevent the mildew. My thought is the shower should not have mildew growing in it so soon. Ok now I’m applying every mildew remover I can think of to remove this mildew but the more I try to remove it the mildew keeps growing in size. I’m beginning to think this is not mildew. What do you think this problem could be?

    • Roger

      Hi Virginia,

      Mildew is caused by damp organic material. Is this in any specific area of the shower floor, or is it in one concentrated area (like the drain)? Different answers would lead to different possible causes.

      • Virginia Fox

        The shower floor is 2″x 2″ tiles. The mildew is not limited to one area, it is sporadic through out the floor. Yesterday we had some one take a look and he seemed to think our guy didn’t install under the tile a waterproofing system. What is your thoughts?

        • Roger

          That is absolutely a possibility. I answer all these questions under the assumption that when a ‘professional’ does it that they have at least installed the minimum – this is not always the case.

  • larry franks

    I ave a travertine shower which has started to leak due grout cracking. Can I someway seal the shower floor.

    • Roger

      Hi Larry,

      No, there is no way to seal the shower floor. The tile is not your waterproofing, it is incorporated into the installation beneath the tile. It needs to be replaced.

      And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay.

  • TheCaptain

    Aha! That shower is similar to the one I am putting in. (I left a comment on another page). I asked a question about wood in contact with concrete.

    Now. I can SWEAR that I saw a paragraph or two about cleaning ‘mosaic’ tile that is held together with those rubber dots. The dots are silicone based and can leave a residue.

    Should I NOT buy that type of tile, and go with traditional ‘netted’ mosaic, or is the problem of ‘greasy back’ on mosaic not that big a deal? Meaning, if I can’t detect greasiness, all is well??

    Thanks again, I think that’s all my questions (for now, but I am still putting in the hardie-backer. Thanks! I was about to use that horrible nasty fibrous cement backerboard – you set me straight! So many things I’ve learned… drywall shims (who would have thought?), make sure studs are aligned with one another… Makes perfect sense. (Amazing how ‘not true’ most framing is.)

    Fair Winds and Following Seas,

    Cap’n Jan

    • Roger

      Hi Jan,

      I don’t believe I’ve ever had any issues with that type of tile. It’s only an issue if the back of the tile is covered with the silicone. The dots aren’t an issue, I’ve used a lot of it.

  • Hudson Reed

    Top advice

  • Jan

    Have a shower bench installed in a walk in shower. The metal framed glass door is a 90 degree angle over the bench but the bench is sloped and it also extends outside the shower stall. The slope of the bench creates a gap where the metal door surrounds it. can the gap be filled with silicon to waterproof it.

    • Roger

      Hi Jan,

      Short of replacing the shower door that is about your only option. So yes, that can be done. Just keep in mind that the silicone will need to be replaced about every 3-5 years or so.

  • Ben

    Always love the explanations (and the humor) – once I’ve heard them they just make sense. My tiled shower is 1+ year in -we’ll see in a few how much I paid attention to Floor Elf ;)