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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  • Beverly

    Had a tub pulled, shower with bench installed. Kerdi floor. Contractor put down mortar and tile on the entire floor, forgetting about the bench. Put the schluter bench on top of tile without grouting first, says it will be fine. My main concern is if water gets in under bench and creates mold. Thoughts?

    • Roger

      Hi Beverly,

      That could be a concern. I would make sure that he uses a sealant like Kerdi-fix to seal the bench to the tile floor to prevent water from getting in there. It won’t get through the bench itself, it would only happen where the bench meets the tile.


    Our house was built a few years so the shower is in pretty good shape but I had to hire someone to recalk around the bottom of our walk in shower because the original calk was looking sloppy and was starting to come off in places. A couple weeks ago I noticed a trickle of water on the tile going towards the drain. I found out the bottom corner of the seat had a little bit of water dripping out so I took off all the calk and put a fan in the shower four days to dry it out. It’s now dry but I’m afraid to have it recalked in case the inside of the seat has moisture in it. I don’t want to have a contractor demo the entire shower but I’m having a hard time finding someone that can remove the seat and re-do just that area. I’ve used the guest bath three weeks and I don’t plan to use my own shower until I figure out what to do. It’s a large L shaped seat. So my question is do I spend thousands for a contractor to demo the whole thing, keep looking for a handyman that can re-do just the seat or just recalk it and hope everything is ok.

    • Roger

      Hi Julie,

      Recaulking is NOT going to do anything to fix an issue, and may actually make it worse by trapping water behind the tile.
      Is anything swelling? Is there cracked grout or other signs of water retention in the framing like a soft wall (squishy, that’s a technical term)?
      There will always be water behind the tile, a properly build shower and bench has waterproofing to prevent the water from getting to the underlying substrate and framing. Water running toward the drain is not necessarily indicative of an issue, it’s suppose to do that.
      If there are other signs of problems the best first step would be to remove part of the tile and benchtop to see what the problem may be and where it derives. At that point I can help you solve any issues that are causing problems.

  • Wendy S

    So we added onto our house, the contractor fully waterproofed the entire shower…..the proper boards, then painted the red waterproof stuff on it. A sealant was applied as well to the tile/grout. We had multiple issues with tiling, but in the end it got done. Flash forward 6/8 months….the entire bench at the seat part has cracked grout all along the top front. What are your thoughts?

    • Roger

      Hi Wendy,

      Water is getting behind the waterproofing on the bench, it’s causing the framing to swell and expand and that is causing the grout to crack. The sealer for the tile and grout has nothing to do with waterproofing.
      It could be a number of things causing this, but they all derive from improper waterproofing.

  • Kevin

    Hi. Do you have a manual on using Kerdi Board from starting at the studs? I see the membrane manual. I’d like to kerdi board manual if its more specific.

    • Roger

      Hi Kevin,

      Not yet, but it’s written. I’m putting the finishing touches on it and it should be available around the middle of the month.

  • Matthew

    This all makes sense, and it looks like my problem is exactly as you have described, a previous owner of the house had the bathroom tiled (10+ or more years ago) on the cheap and now I am paying the price by not having a second shower during the pandemic.

    My question is this, while I know that a more permanent fix is required (as described above) and it is on the schedule after one or two other projects, what is the life span of a temporary solution like caulking the joints?

    • Roger

      Hi Matthew,

      Zero life span. It MAY slow it a bit, but there is already water behind your tile, more water will get behind your tile. The crack in the grout is not where water is getting into it (some, but definitely not most). Caulking will do nothing significant for you. Sorry.

  • Jenny

    We had water leaking through the floor, puddling in the basement. It appeared to be coming from the bench, not drain. A contractor is in the process of rebuilding the frame. The wood frame had no water barrier (our builder was terrible). You mention grout cracking and frame swelling as signs of bench not being properly waterproofed. We didn’t have those signs, just leaking to basement, so do you think there is a bigger problem?

    • Roger

      Hi Jenny,

      Those are the most common signs of it, but they aren’t ALWAYS present. Water and wood interact in several different ways. The bigger issue is no waterproofing or barrier. Provided those were remedied it should solve the problem.

  • Amanda

    I don’t know if this is the right place to ask this, but I hope you can help! We recently bought our first home and there is a marble (or marble-esque) bench. It has a ledge that protrudes an inch or two and when cleaning under it, I realized it is moldy. Upon further inspection, there is a gap between the bench and the tile which I’m assuming is a problem. Should we use silicone caulk on this immediately, or is this gap intentional for some reason?

    • Roger

      Hi Amanda,

      It could be there for a number of reasons. In a properly waterproofed shower it really doesn’t cause any issues. However, it may be there because it was initially grouted rather than caulked and the grout cracked out of it. That may not be a deeper issue, in which case you can simply silicone it. It may also be there because it was originally filled with either grout or caulk and water seeped into the substrate behind it. If that is not properly waterproofed then the water will lead your substrate to swell and, in turn, allow whatever was initially in that gap to come out. In that case you’ll need to remove either the top or a row on the front to get to it and try to repair it. Can you shine a flashlight into that gap and see what is actually behind the tile there?

  • 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 ;)