Preparing a Shower Wall for Tile

by Roger

If you need to decide which method is best for you I have a free shower waterproofing manual that you can download here. Shower waterproofing manual. Go get it – it’s free! And I’m not gonna use one of those damn annoying pop-ups! I hate those things…

There are several ways to prepare the wall of a shower for tile. Depending upon what was originally there, what stage the shower rebuild is currently in, and what type of tile you plan to install plays a minor part in choosing which method to use.

The most critical aspects of which product to choose are: how much work you’re willing to put in and how much money you’re willing to spend. The end result should be the same – a waterproof box. The methods used to accomplish that vary in effectiveness and cost. So we’ll start with what I consider the most bullet-proof method.

Kerdi Shower System

A company called Schluter makes a shower system called Kerdi. The entire system, which can include everything from the wall membrane down to the entire shower base, is considered by many professionals to currently be the top of the line in shower substrates and waterproofing membranes. And no, I don’t work for them. I don’t owe them money. And they don’t take me on those all expense paid vacations to Bermuda – bastards. I like their products anyway.

The waterproof membrane made by Schluter is called . . . well, Kerdi. It’s bright orange and you can see it from space. It is installed over regular drywall or cement backerboard with regular thinset. It makes your shower a big bright orange waterproof box that glows in the dark. Okay, it doesn’t glow in the dark.

The material is difficult to describe with words, it’s kind of like a fleece-lined rubber(ish) membrane. I like it for two reasons: It is the best available and it happens to be the easiest, least work intensive option (once you are used to working with it). While there is a fairly large learning curve to effectively work with it, Kerdi is fairly easy and very well documented. There is a wealth of infomation on the internet about it. Just Google Kerdi. Go ahead, I dare ya. Noble company also makes a similar membrane called NobleSeal, but it isn’t pretty bright orange.

Liquid Membranes

After Kerdi, a brush or roller applied liquid membrane such as RedGard works very well. It is applied with a brush or roller like a thick paint. It’s bright pink. You coat it once, after it changes to red, coat it again. Usually two coats is sufficient for any shower (except steam showers). After is sets overnight just go in and stick the tile to the membrane itself. It is a bit expensive, but they are also simple and quick to install.

There are several of these membranes on the market, the most common being Redgard. My favorite is Laticrete Hydroban. Laticrete also makes Hydrobarrier and Mapei has Aquadefense. They are all pretty much comparable.

Preparing shower walls with RedGard

If you are building a shower and want a manual describing the entire process you can find it here: Liquid waterproofing membranes for shower floors and walls

Cement or Fiber Based Backerboard

If you don’t want to spend the money for Kerdi or RedGard, this is your next best option. These are products such as Durock, Hardiebacker, and Fiberboard. While the product itself is not waterproof, it is water-resistant. The backerboard will actually hold water, as in water will soak through it. There needs to be a vapor barrier put up between the wall studs and the backerboard.

The unique thing about these products is that, although they are not waterproof, they will not become unstable with moisture. (That just means water doesn’t make it swell up.) To use these you must first install some type of moisture barrier over the wall framing. Get a 4 mil or thicker plastic (mil is just the thickness of the plastic) which can be purchased at places like Home Depot, and staple it to the studs of the wall framing. You can also adhere it to the studs using silicone. Completely cover all areas from the tub to the ceiling. The backerboard is then screwed onto the studs to make your shower walls. Then you just stick the tiles to the wall and shower away.

How to install backerboards

I also have a couple of manuals describing the entire process from the wall studs all the way up to a completely waterproofed shower substrate ready for tile. You can find them here:

Waterproof shower floor and walls manual

If you have a tub or pre-formed shower base and need to only do the walls you need this manual:

Waterproof tub and shower walls

Denshield

Denshield (and others like it) are similar to drywall in that they are lightweight and easy to install.  It is a waterproof core laminated on each side with a fiberglass based face. It is installed like drywall except you need to run a bead of silicone between the sheets to waterproof the seams. You then need to use fiberglass mesh tape over the seams. It does not require a moisture or vapor barrier behind the sheets. When properly installed Denshield is an adequate tile substrate for shower walls and relatively affordable compared to alternative methods.

If you are building a shower and want to use a topically-faced wall substrate you can find that manual here: Building a shower with a traditional floor and topically-faced wall substrates

If you are just tiling around a tub or pre-formed shower pan you can find that manual here: Topically-faced wall substrates for tubs and shower walls

Plain Drywall *DO NOT DO THIS!!!

Yes, you can do it if you must. I absolutely do not recommend this! But I’m also realistic enough to know that if you decide this is what you’re going to do, I’m not gonna be able to stop you from here. You can not just go up to your drywall and start sticking tile to it – ever. There needs to be a moisture barrier between the drywall and the framing. At least then when water gets behind your tile and grout and disintegrates the drywall it won’t disintegrate your wall framing as well. Remember, if water gets to one of the studs not only will you be replacing the shower, you will need to do some serious repair work to your wall framing and possible structural work. Please also note that using this method runs the risk of parts of your wall literally falling apart if it gets wet – drywall disintegrates in water.

And it will. So don’t do this!

Unsuitable substrates for shower walls – no matter what you’ve been told

  • GreenBoard, also known as green drywall. Never use this or you’ll get a lot of practice replacing showers.
  • Backerboard without a moisture barrier.
  • Drywall without a moisture barrier. (I do not recommend drywall as your substrate at all.)
  • Any type of plain wood or plywood. Ever. No, painting it makes no difference.

I’m certain there are a lot of things I’m not thinking of that someone else will. If you wouldn’t let it set in a swimming pool for a week, don’t use it for your shower walls. That should clear it up.

The golden rule

Although there are many products that can be used for your shower wall, many should not be. Regardless of which method you choose one thing to keep in mind is that you need to have some type of waterproof membrane between your tile and your wall framing. Kerdi membranes and RedGard are both waterproof membranes that go directly on the wall. Plastic stapled to the frame before installing your substrate is also acceptable.

The main thing you need to ensure is that no water reach your wall studs – ever. Wood swells with moisture and the only place that excess swelling is going to go is right into the back of your tile. Remember, your tile is not waterproof so you want to adhere your tile to a substrate that is as waterproof as you can make it.

If you need to decide which method is best for you I have a free shower waterproofing manual that you can download here. Shower waterproofing manual. Go get it – it’s free!

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Steve

Roger ,so you recommend a moisture barrier over the framing even with hardi board covered by a Kerdi membrane ?

Reply

Roger

Hi Steve,

No, I don’t. Where did I recommend that?

Reply

Axel

Roger,

I am in the process of dry fitting my floor tile and noticed I had somehow overlooked a small section of wall that is way out of flat (+1/4″) which will also be tiled. Please don’t ask me how, a dog may burst into flame, or just me. When I go back to lay my floor tile, could I use a little of my thin-set to level that low spot on wall like a SLC? Then later, tile as usual. If so, how long should I wait until I tile. It was my plan to do it in a day or two.

Reply

Roger

Hi Axel,

Yes, that will work fine. You can tile over it the next day.

Reply

Phillip

I am installing kerdi over wonderboard and tiling it with painted back glass tile in my shower reno.
regarding the unmodified thinset for the kerdi – should I skim coat the wb and let it dry prior to install the kerdi? I read somewhere that could provide a better bonding to the kerdi, as the thinlayer (of unmod thinset coating) would allow the fresh layer for the kerdi to remain softer (drying too fast)
– as skim coat I literally talking about really spreading it thin, almost sponge it in.
Same would go for afterwards:
as the tile mnfr recommends modified thinset, I talked with kerdi, and they said the one selected (laticrete 254 platinum) is a better for the tile, BUT I should also skim coat the kerdi after installed (not sure any longer if had to be mod or unmod). Could you educate/correct me a bit about all this?
Thanks

Reply

Roger

Hi Phillip,

Yes, skim coat the wb first, but you don’t need to let it cure before installing the kb. (Why, by the way, are you installing kb over wb???). You also do not need to let the 254 cure before installing the tile, but you can use the 254 over kb. Skim coating both allow a fresh substrate which will not suck moisture from your thinset as well as getting a proper bond by filling the pores of the substrate first.

Reply

Phillip

Hi Roger,
Thank you for your insights.
Yes, I am an over-doer of some sorts :) nothing wrong with plain drywall, but it’s a sturdier installation IMO. Looking back now, I should had gone with kerdi boards – it’s amazing how stiff and sturdy it becomes with thinset and/or kerdi-fix
regarding the skim coat for before and after the kerdi membrane – do both have to be unmodified? I would assume the first one so, because it’s what is needed to bond the kerdi anyway; but later on the membrane – before the laticrete, should I go with unmod or use the laticrete already?
last but not least, I bought by mistake a bag on unmodified Custom Building thinset – can I use it to skim coat the WB and then to fill in the ditra squares (yes, I am using it for the floor) before going with a layer of TEC unmod to lay the floor tiles? ( it’s a bit too sandy as you probably now)
Thanks once again
Phillip

Reply

Phillip

btw, I called it wonderboard, but actually I used hardie backer boards just for the shower area

Reply

Roger

You can fill the ditra with the custom stuff. You do not need to use unmodified for your skim coats. The unmodified ‘suggestion’ has nothing at all to do with whether or not it will bond. Modified thinset bonds to kb just fine (better, actually).

Reply

Pablo

Dear Roger:
Thank you for your great site and advice.
I just finished installing 12×24 porcelain tile over hardibacker painted with two coats of redguard. Unfortunately I did not read enough before I started and I used Omnigrip on the walls of the tub area. From what I have read I believe I should have used a non-modified thinset since it dries without air and air is lacking between the redguard and the porcelain tile.
I did a tub bath and a shower bath this way 3 years ago and both have never had a problem. I had let the tile omnigrip dry out since I got distracted on another project, for 3 weeks before grouting and maybe that was what saved me.

I know I was a fool to not use mortar, but all the tiles are cut and attached now.

Three weeks have gone by on my new tub bath. I got tied up again, haha. On this new job the tiles feel tight. I am going to place a space heater in the bath to ratchet up the heat and leave it for another week before grouting.
My fear it that once the bath is used, and as humidity creeps in through the grout, I do not want the Omnigrip to soften, I was planing to grout the 1/16 to 1/18 horizontal gap between the tiles and the tub with non-sanded grout.
I wanted to know if you thought it would it would be a good idea to leave that gap as a weep exit for the humidity since the Omnigrip trapped between the redguard and the porcelain is susceptible to softening.

Reply

Roger

Hi Pablo,

It honestly makes no difference whether you do that or not. The outside perimeter of the mastic is likely cured, the inside, beneath most of the tile, is not. The reason they seem bonded correctly is because of this, if you pull a tile off you’ll have a big glob of uncured mastic in the center of the tile surrounded by a cured bead of mastic around the perimeter. It’s simply an improper installation and nothing you do from this point, short of replacing it, is going to make it correct or limit the chance of failure. And redgard is used with modified thinset, not unmodified. Schluter is the ONLY company that wants unmodified.

Reply

Phill

I am having problems shimming the studs above my shower base. So my question is how do you shim studs that have a bow in them or that are slightly twisted? Any help would be greatly appreciated.
Thanks, Phill

Reply

Roger

Set a straight edge along the stud and place shims behind it until you have enough shims in the correct areas to make it flat.

or

Shave down the studs with a planer until they are flat and plumb.

or

Sister new studs next to the bowed ones so they stick out flush with the outermost part of the bowed studs.

Reply

Idris

Is it acceptable to attach hardi backer to studs without a vapot barrier if you red guard the hardibacker after taping and mudding the seams? Thank you, your site is amazing!

Reply

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