One of the problems with waterproofing a shower is the fact that you NEED to have holes in it. The cutouts for the shower head, shower or bath controls and any other fancy stuff you saw in that magazine. The problem with holes in a waterproof shower is that they make it not so waterproof.

So how do you waterproof a hole? (Please DO NOT email me with the punchline to that joke!)

Whether you have utilized a topical waterproofing like Hydroban or Redgard (liquid) or Kerdi (sheet), or you’re using the traditional method with a membrane behind your substrate, the answer is silicone. You need to use 100% silicone, none of that acrylic silicone or any of that stuff that sounds fancy (but doesn’t work long-term).

First a little about silicone. A lot of people ask me which silicone is best. For the purposes of most shower applications silicone is silicone. If it’s 100% silicone there isn’t (for all intents and purposes) any difference at all. They are all the same. Just grab a tube of silicone and stop overthinking it! :D

Back of tile with holes cut out

Picture 1

Now once you get your hole cut out in your tile flip it over so you’re staring at the back of it. Have a beer Pepsi to congratulate yourself for such a fine looking circle! (Picture 1)

If your hole spans two or more tiles then the technique is the same, but you should have two beers Pepsis.

Bead of silicone around hole perimeter

Picture 2

Now all you need to do is shoot a large bead of silicone all the way around the perimeter of the hole. (Picture 2)

You can click on any of these photos to view a full-size version.

When you comb thinset onto the substrate you want to scrape away the area around where the hole in the tile is. (Picture 3)

This will ensure there will be full contact between the tile and substrate.

Hole cutout in shower substrate

Picture 3

Then just slam your tile up there.

Okay, don’t slam it up there, place it up there carefully and press firmly to ensure full contact.

What this does is create a dam of silicone around the perimeter of your cutout. When water gets behind your tile (and water WILL get behind your tile!) and runs down the wall, it will run around the bead of silicone and continue down the wall into the tub or shower base and into the drain.

Ensuring full contact between tile and substrate

Picture 4

If you want to, pull the top of the tile back off and check to make sure you have complete contact with the silicone bead and the shower substrate. (Picture 4)

If you get enough silicone on there you’ll be able to run your finger along the perimeter of the cutout after you install your tile to smooth the silicone. It’ll be a mess – just like picture 5.

Tile installed with waterproofed cutout

Picture 5

Once you get your escutcheon (the metal cover plate) on there no water will enter through the front of the tile, then any water behind your tile will run around the dam.

You can also do this with the cutout for the shower head if you want to, but it’s not as imperative up there. It never hurts, though.

If you are using the traditional method and have your waterproof barrier behind your substrate (like in these pictures) you’ll need to silicone the perimeter of the barrier to the back of your backerboard. This creates the same waterproof dam on the backside of your substrate as well.

I do not have a picture of that. Because I’m a slacker. Get off my ass about it. :D

I will call him George...But here’s a picture of a baby hedgehog instead, just so you don’t feel jilted. And an apple. Hedgehogs like apples.

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  • Dewey Galloway

    Hello, can the silicone procedure you explained in your post be used with Mosiac tiles since they don’t form a solid piece to keep silicon from oozing through each of the small sections held together by the mesh on the back?

  • John McDonough

    Can you just silicone the part where the cement board meets the drywall Instead of taping?

    • Roger

      Hi John,

      You can, but you still need to tape and mud it. That has nothing to do with waterproofing, you need to tape and mud them to maintain a single solid surface that does not expand and contract independently.

  • John McDonough

    Should I silicone the opening you mentioned on the cement board section? I’ve used mapei’s aquadefense.

    • John McDonough

      Nvm that’s a yes… this is an awesome thread

  • Matt


    I have a drain clean out from the kitchen sink on the main floor that’s at the base of my basement shower. I need to leave this clean out accessible, but how do I keep water from running down the shower wall tile and infiltrating this clean out door. The opening is 5″×8″, and at the base of the shower wall. Thanks in advance.

    • Roger

      Hi Matt,

      Either move the shower wall or build a bench over it. The only two things I can think of offhand. If it’s at the base of the wall water will get to it.

  • John


    I feel like I keep finding out things I should have done differently after it’s a bit too late. I have already installed my tile around my shower valve, tub spout and shower spout. I don’t need to rip it out to add silicone, do I? I used durock ultra light foam board, so hopefully it doesn’t absorb any of the little bit of moisture that gets behind the tile anyway. I just feel like it’s about impossible to do a tile job exactly right! I just want it to last a long time. Thanks for your time.

    • Roger

      Hi John,

      No, you do not. You can silicone between the tile and backer around the hole, but there’s no need to tear tile out to do it.

  • Kate

    Hi Roger,
    Thanks for sharing all your knowledge with us. I have been reading through your manuals, and they are helping me feel more confident about tiling.

    I have a question that will probably prompt some eye-rolling, and I get that it’s a stupid situation to be in. We are renovating our 150 year old house, and in the upstairs bathroom, I found a stupid dead space that, if we rearranged some things, would allow us to have a tub in there. Five years later, we managed to finally get to tub stage. Everything in this bathroom (and this house) has been do-or-die to the tune of fractions of an inch. Well, in an effort to save me from losing more space in my already tiny “elf closet”, our carpenter framed our tub wall that holds our plumbing with a 2×4, instead of a 2×6, which was great, because we could leave the stupid little closet alone. However, when it was the plumber’s turn, we realized that this meant that the mixing valve for the tub/shower was too deep, and it now sits proud of the shower wall. Plumber advised me to have my tile guy build it up with mud.
    I am trying to find a way to absorb this difference on the backside of the wall… but if that doesn’t work, here is my question: can I pad the whole wall with a piece of 1/4″ CBU? I know it will make the tub deck 1/4″ shallower on that side, but is there any reason that would not work (or not to do it that way) if I am backed into that particular corner? I assume thinset and screws to fasten?
    Thanks for your help.

    • Roger

      Hi Kate,

      Yes, you can. No need for thinset behind it, just screw it to the studs through your existing substrate. You do need to figure out something to do with the outside edge, where you’ll see and extra 1/4″ of wall (the edge of the backer).

  • Marcy

    Hello. I am in the middle of shower remodel. Size would not accommodate a prefab pan. Floor is concrete. It was suggested to me to do a custom fiberglass pan. So the contractor came and layed cement and did the flow or slope for drain and plumber has done what he needed to do so today they came back and did the fiberglass coating over the concrete floor and frame. My question is what happens next? We are using tile for walls and mosaic for shower floor and I want to know if any additional waterproofing materials other than backer board need to be applied before or after the backer board and was told not to put any holes in fiberglass coating so is there is need to do that that at all for any reason?

    • Roger

      Hi Marcy,

      You still need waterproofing over the backer above the fiberglass, but nothing is needed over where the fiberglass is.

  • J Walls

    Regarding a shower with Hardi substrate and Kerdi waterproofing—–
    Due to inaccuracies in cutting valve holes in the Hardi, the Hardi holes (in some cases) are a little bigger than the escutcheon seals (up to 3/8″ more on radius).

    My plumber and tile guy say not to worry—they’ll just make the tile hole smaller than the Hardi hole, so the escutcheon will seal against the tile.

    OK, but what about the silicone dam behind the tile?
    I can still put a silicone dam around the Hardi hole (on top of the Kerdi) as shown in this article, but the silicone dam would be slightly larger in diameter than the escutcheon seals (by up to 3/8″ on radius). So…………..

    1) Is this too insignificant to worry about? It seems that very little water would penetrate that small exposed annulus (3/8″ wide) of tile face that is inside the projected radius of the silicone dam. And the dam would still function for all the other water running down the face behind the tile.
    2) I could abate some of this by siliconing the OD of the escutcheon instead of relying on its (smaller OD) rubber seal. Is that common practice?
    3) I have access panels on the back side of the wall. Should I attempt some sort of additional or extended silicone dam from the back?
    4) I have bought larger OD escutcheons where available, but some not available.

    • Roger

      Hi J,

      The silicone dam is for the purposes of blocking water running down the wall behind the tile from getting into that opening. No water is going to get into that 3/8″ radius, nor through the front of the escutcheon. Just do the dam, it can be larger than the cover.

  • Matloc

    Hi Roger!

    My shower project is coming along (slowly but surely), but I have a question regarding one of my walls.

    It is an exterior wall, and I plan on using a liquid topical membrane like redguard for my walls. Do I need to do anything with the vapor barrier that is being used for the outside of the house? I just don’t want to create a mold sandwich.

    Your blog is sent from bathroom remodel heaven, if such a place exists 😀

    • Roger

      Hi Matloc,

      I normally just cut slits in the barrier in the stud bays. They don’t have to be very long, just enough for any vapor to dissipate.

      • Matloc

        Thanks Roger!

        Alas, I have one final question. My exterior wall has foil faced foam sheathing (1/2″ thick), and behind that are the studs and normal fluffy insulation. Regarding my shower pan liner, is it okay to tack it right on the foil faced foam sheathing (into the studs of course), or should I take all that down and just leave the studs and fluffy insulation? I live in michigan where the winters are cold if that helps with the answer.

        Again, thank you so much. Your blog has been THE most helpful thing on the internet for my remodel.

        • Roger

          You can tack right through it.

  • Jack

    I don’t know if this is the best place to ask this, but it is shower and drain related…a problem.

    The shower was never built quite right. The lowest portion of the floor is about 6″ further in than the drain, so in order for all the water to be out of the shower at the end of the day, one has to squeegee it toward the drain.
    I have plenty of room under the floor to access the drain and pipes there….what I’m curious about is an idea of simply adding a second drain into the floor. I have no spare tile to match what is in place, and it is quite solidly bonded as far as I can tell. So the thought is to simply add a second drain where the first one SHOULD have been in the first place. I could tie them together below the floor….BUT….I have no clue how to make sure I have a seal around my existing membrane so as to not have problems with water doing what it does so well and go where I don’t want it to go.
    Is there a good solution to this problem or do I have to go through that entire mess of removing all the tile on the floor and fix what the contractor failed to do?
    I’ll have to get you a six pack for this probably…two beers isn’t enough.

    • Roger

      Hi Jack,

      There really is no easy solution to it. Adding a second drain and tying it into the existing membrane would require at least partially removing floor tile, doing all that, then replacing deck mud and floor tile. With that much work at that point it would actually likely be easier to replace the floor. You can also get a ‘drain extender’, which raises the drain, then pack another mud deck over the existing tile, correctly sloped, and tile it. That would eliminate the need to remove the existing mess.

      • Jack

        So that brings my next question: do I need to do more than simply pack the new (and hopefully correctly sloped) mud deck onto the existing tile? Do I need to prepare that tile with anything? I’ve never tiled over existing tile.

        • Roger

          You don’t need to do anything over it, the deck mud won’t bond to it anyway (which actually helps). Just install the new mud deck and tile away.

          • Jack

            Thanks for that information

  • Kay

    Hi Roger,

    You may have answered this elsewhere, but I was reading your traditional shower waterproofing guide and had a quick question. We are putting tile over a tub. For the gaps between backerboard and drywall, do you also tape and mud those? If so, what do you do with the plastic moisture barrier? Do you leave it sticking out from below the backerboard and over the edge of the drywall? If so, how far?

    Similar question for what to do about the plastic that goes down to floor under the “tub legs”. Do you trim it and where does the edge go relative to the flooring – presumably not below :) (in this case the drywall was already removed for the legs, so we put backerboard there.)

    Thanks for your help!

    • Roger

      Hi Kay,

      Yes, you tape and mud that seam as well. I tuck the plastic behind the drywall or cut it right at the drywall. No considerable moisture is going to get to that area anyway. At the bottom of the tub legs I just cut is off at the flooring. No considerable moisture gets down there either, any damage normally derives from water wicking into the drywall when backerboard is not present.

      • Kay

        Great, thanks for the info! good luck getting that ostrich saddle off your hands…

  • John Walls

    I get the general idea, but I’m having difficulty understanding pic #3.
    1) Is the thinset applied up to the opening in the substrate and then scraped away (like a 3/4″ gap)? If so, will the silicone bond? —doesn’t bond to thinset (wet or dry), right?
    2) I’m using Kerdi over Hardi. Do I need to seal the cut face of the Hardi with a smear of silicone also?
    3) What’s the mesh tape about in the pic? Just happened to fall on a seam in the substrate?

    • Colleen

      I was also wondering about #1 and #3.

  • Rob

    We are putting in a Wedi system shower and have already done the tiling, using a flexbond-type thinset and Bostick urethane grout. Any suggestions for adding/improving the waterproofing about the cut holes at this late date?


    • Roger

      Hi Rob,

      Either the technique above or you can use schluter valve seals on them (just google it).

  • Bandolin

    Brilliant! You have no idea the headache you just solved.

  • Roger

    Hi, First of all, great name. Secondly, thanks for all of the information.
    I feel like I am missing something obvious here. I imagine water running down the front of my tile and getting behind my escutcheons then making its way through the 2 inch hole through my Kerdi and backer board and into the inside of my stud wall. There is a little foam thing inside my escutcheons, but I have little faith in it.

    • Roger

      Hi Roger,

      Water doesn’t run sideways. :D It will run around anything in the path downward. While it may cling to the side of the escutcheon and be channeled sideways for a bit, as soon as it hits any type of barrier it will begin to run down again.

  • Rod

    Hi Rodger,

    What do you think about Kirdifix? As I have a brand new tube of the stuff. should i take it back, and buy 100% silicone?

    • Roger

      Hi Rod,

      Nope, use it. That stuff is indestructible! :D

  • Tina

    Hi Roger,

    I am still a little confused about how to waterproof around the holes. I am wondering what I should do before I even get to the tiling part. I am getting ready to apply thinset and mesh tape to all the seams. Do those faucet and shower head holes get thinset or tape? Then I will apply redguard to it? Do I just paint the redguard right up to the holes? Or am I just supposed to wait to do any waterproofing for those holes until I apply the tiles?

    Also, am I supposed to thinset and tape the space between the cement board and lip of the tub? Am I supposed to apply silicone to that space or just caulk? Do I not worry about caulking that space until after all the thinsetting, taping and redguarding?

    Thank you Roger!

    • Roger

      Hi Tina,

      Paint the redgard right up to the holes. It will not be technically waterproof until you install the silicone and tile. However, once you get those installed the only way water can get into them is to fly sideways – it doesn’t do that. :D

      No thinset and tape between the backer and tub. Silicone that space, then paint your redgard down over it all the way to the flange.

  • Kris

    Okay, so you have the back side of the tile sealed with silicon so the water runs down the back side, around the hole, and in to the tub. But wait, I just sealed the gap where the tile meets tub flange, also with silicon, so there is no way for the water to drain into the tub! It will just back up and eventually (over the years) saturate the substrate! What to do now?

  • Bobby


    I’m building a tile shower with Kerdi membrane, and the Schulter shower base kit (I read your manual on waterproofing with Kerdi – it’s excellent!).

    I understand how to seal the pipes and mixing valves, but what about the ‘other’ valve openings (I’m using a hansgrohe thermostatic valve, and have three other valve openings for the shower head, hand shower, and rain shower). I know I can use silicone around the opening behind the tile so water behind the tile can wick around it, but how do I prevent water from getting behind the substrate?

    Thanks for your help,

    • Roger

      Hi Bobby,

      I don’t quite understand what you’re asking. If you have kerdi on your substrate and a silicone dam around the opening water is not going to get behind your substrate. Maybe I’m just not understanding your concern correctly?

      • Bobby


        I guess my concern is sealing up the kerdi membrane properly around the valve opening through the substrate. The valve manufacturer supplied the typical plastic placeholder/spacer that temporarily attaches to the valve and protrudes through the substrate. It’s about 1.5″ in diameter. If I place the kerdi membrane up to that, and then it is removed when the trim is added, what prevents moisture from getting through that hole?

        But, perhaps when everything is put together, that isn’t really a concern?

        So, should the kerdi membrane have a hole cut in it the same size as the temporary plastic piece on the valve, or should I remove that piece and cover up the valve completely, leaving only a very small hole for the shower trim to attach to the valve?

        Thanks for your time,

        • Roger

          Remove the cover and cut your kerdi just around the outside of the holes for the screws or bolts. Once everything is on water isn’t going to get through it.

  • Justin


    Great site my man. I just tiled a floor this weekend based your great tips. My next project is to tile a shower using Kerdi membrane. I have one question though which I’m unclear about. Do I absolutely need to use kerdi fix around the mixing valve and tub flange or can I use 100% silicone?

    • Roger

      Hi Justin,

      You can use the silicone.

  • Dan

    Hey Roger, just bought your kerdi bundle and read the kerdi book top to bottom. It’s great! I plan to use a moentrol 3330 Three Function mixing and transfer valve, and of course, the kerdi mixing valve gasket is not big enough.

    So my question is similar to Steve’s above, but with one caveat. Moen states in their instructions to keep the plaster ground in place during installation of the trim and that it should sit flush with the finished tile. It seems that your method above is perfect for this type of installation, but before I go hacking this together, I just want to confirm that this is the correct course of action.

    Thanks in advance.


    • Roger

      Hi Dan,

      While I normally always advocate to follow manufacturers recommendations I have always removed plaster guards from every valve I’ve done a shower in. And I’ve done a lot of moens. I don’t know why they would want you to leave it in there unless it’s part of the seal for their trim. But yes, it will work for your situation as well.

  • Steve


    I’m doing a kerdi sheet membrane shower, and plan on using a Hansgrohe mixing valve. What should I do?

    OK, maybe you need more info. The kerdi mixing valve seal is 4-1/2″ and the Hansgrohe ibox requires a 5″ hole. It comes with its own seal, but it’s not kerdi, obviously.

    Silicone on the “plaster guard”…..enough?
    Use included rubber seal…how to attach to the kerdi?
    Something more or less obvious?


    • Roger

      Hi Steve,

      The plaster guard is removed before the trim pieces are put on. They are meant to discard. You can bond the rubber seal to the kerdi with kerdi-fix.