Waterproofing fixture cutouts in shower tile

by Roger

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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John Walls

Roger,
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?

Reply

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?

Rob

Reply

Roger

Hi Rob,

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

Reply

Bandolin

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

Reply

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.
Thanks

Reply

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.

Reply

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?

Reply

Roger

Hi Rod,

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

Reply

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!

Reply

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.

Reply

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?

Reply

Roger

Hi Kris,

Weep holes. :D

Reply

Bobby

Roger,

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,
Bobby

Reply

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?

Reply

Bobby

Roger,

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,
Bobby

Reply

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.

Reply

Justin

Roger,

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?

Reply

Roger

Hi Justin,

You can use the silicone.

Reply

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.

Dan.

Reply

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.

Reply

Steve

Roger,

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?

-Steve

Reply

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.

Reply

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