Now that you have your curb built and your pre-slope done (if you haven’t done this yet check out How to create a shower floor, Part 1) you are ready to install your waterproof liner.

Purchasing a waterproof liner

When you order or buy your liner you need to get one large enough for your shower. The liner you get has to be at least one additional foot larger than each of your measurements. For instance, if your shower floor is three feet by five feet your liner needs to be four feet by six feet. This allows enough to run the liner up the wall behind your backerboard six inches each way. You also want to purchase two “outside” corners for your curb. These are pre-formed corner pieces to waterproof the ends of your curb after you cut the liner.

I usually order mine two feet larger in each direction. Six inches is the minimum. Specifications state that your liner must run up the wall at least three inches above your curb. So if your curb is three inches high your liner needs to run at least six inches up each wall. I usually go a foot above the curb – overbuilding your shower is rarely a bad thing.

Preparing your shower floor for a waterproof liner

Image of a sandy shower mud deck

It's supposed to be sandy!

Before you install your liner I need to say type this: your preslope will be sandy, it’s suppose to be sandy – it’s normal, don’t panic. If you have any high areas in your preslope you may want to scrape or sand it down so it runs in a flat, straight line from the wall to the drain. Notice I said typed “flat, straight” and not level – if it’s level water won’t drain.

You can scrape it down with a regular razor scraper or sandpaper – yes, sandpaper.  If there is a significantly large dip in your pre-slope you can fill it with more deck mud. You’ll need to coat the pre-slope with thinset under the patch to ensure it will stay put. Don’t get all OCD about this, it doesn’t have to be perfect. Just make sure there are no major humps or dips and water will run from the wall to the drain without problems.

The next thing to do is take a chisel to your wall studs. You weren’t expecting that, were you? You want to notch out your studs about 1/8″ up to the height of the top of your liner. This is so you can place your backerboard over the front of your liner on the wall without them jutting out at the bottom. It allows your walls to remain flat all the way down to the shower floor. You will create “cavities” in your wall studs for the liner. 1/8″ is a bit larger than the thickness of your liner but it’s better to be larger than smaller.

When you place your liner in the shower you will be folding the corners so you want to allow enough room on one of the corner studs for three layers of the liner. I usually notch my corner studs out 1/4″. This allows enough to keep your corner square after the walls are up.

Placing the liner in your shower

Image of a shower liner placed on pre-slope

Liner placed over pre-slope

Now it’s time to lay your liner in the shower and get it all lined up. DO NOT cut anything until you have the liner exactly where you want it. Make sure you have the top half of the drain flange removed before you place your liner over it. I’m not talking typing about the round part that unscrews, I mean the top half of the lower part which bolts onto the lower half. After removing the top half of the flange replace the bolts, this will serve as a guide when you cut the liner.

Center your liner in the shower with the ends running up the walls evenly. Also make certain you have enough of the liner draped over your curb so that you can attach it on the outside of the curb. I will usually place it so that the liner drapes up and over the curb all the way to the floor on the outside of the shower.

Cutting the hole for the drain out of  your shower liner

Image of the drain cut out of a shower liner

Drain hole cut out of liner

After you have it properly positioned you can cut out the hole for your drain. Do this very carefully – there is no second chance. Take your utility knife and poke a hole through the liner directly in the center of the drain. From there cut in a circular motion toward the outside of the drain in a spiral. Only cut it  out to the outside of the four bolts which attach the top half of the flange to the bottom.

Image of silicone under liner around the drain flange

Silicone under the liner around the drain

Remove the bolts from the flange. Now you need to place a bead of silicone under the liner around the perimeter of the lower flange. The easiest way to do this is to place the nozzle of the tube of silicone into the hole you just cut for the drain. Place a good size bead around the lower flange outside of the bolt holes, don’t get any in the bolt holes. This prevents any minute amount of moisture from getting under you waterproof liner. Press the liner into the bead of silicone all the way around the drain to ensure full contact.

Image of prepared liner

Prepared liner ready for top slope

Now you can bolt the upper half of the flange to the lower. Do not overtighten the bolts. You want to squeeze the liner between the two but not so much as to crack the flange – they are only plastic, after all. That’s it, the drain is finished.

Now take your liner and place it up the walls into the notches you cut out of the studs. You can nail or tape the top of them to hold them in place. Only place one nail into the very top of the liner, never lower. In the corner you will fold the liner over on itself, never cut it. Place the folded part into the larger notches. There should be enough room in the notches so your backerboard will set flush onto the studs.

In my next post I will cover how to cut the liner for your curb and make sure it’s waterproofed properly.

{ 284 comments… add one }

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  • Jay Bunderson

    This is Jay B again…Thanks in advance for helping. If I cut the denshield and replace the pieces later, I plan to seal the edges with silicone and tape with a fiberglass mesh tape. Buy what kind of mud? Also the drywall guys taped and mudded some of the Densshield joints. I should cut those out I suppose and seal with silicone?
    Thanks again.

  • Jay Bunderson

    My Densheild brand backer board is already installed down to the floor. I am thinking that I need to cut 7 or 8 inches out along the concrete floor, notch the wood studs and replace the backerboard pieces over the liner when done. Sound right to you?

  • Alicia

    Silly question, I am doing a curbless shower on slab 60”x36” with a linear drain. The linear drain has a waterproofing membrane already attached, and I plan on using the same manufacturer’s waterproofing system on the floor and walls. Do I still need to do a liner, or does the waterproofing membrane take the place of it?

  • Mike Tursellino

    Roger I noticed you cut the hole in the liner at the drain on the outside of the bolt holes. Goes against all others on the web. Most do x cut over bolts and x for the hole. I see how your way could work better as I feel the clamping pressure would be better on the liner since there is no liner under part of the clamp. Also weep holes would probably drain better. Is that why you do it that way? Maybe I’m overthinking this lol. Great stuff. Hope to lay preslope this week.

  • Kate Deters

    Hi, Roger. I just have a few little divots after doing my pre-slope. What is the recipe/type of thinset I should use to fill them in before laying down my shower liner? And how long do I have to let the thinset cure before moving on to the liner?

    • Kate Deters

      Hi! I have another question. I fixed my divots with thinset – I determined (perhaps erroneously) that they were minor enough as to not require more deck mud. Now I’ve installed the shower pan liner, but it seems like the creases in the shower pan liner are larger than my divots were! How do you recommend smoothing out the rubber membrane? Man, I’m wishing I could be your apprentice for a day just to (start to) figure out all the subtleties of getting this perfect (adequate is more like it).

      • Roger

        Hi Kate,
        Once you begin packing deck mud on top of that liner it will flatten out. The liner won’t stay like that under the weight of deck mud.

  • John

    Hi Roger,

    Quick question about creating “cavities” on the studs.
    I have metal studs what to do in this case?

    • Roger

      Hi John,

      In that case you’ll need to place shims on the studs above the liner to shim out the backer so it’s flat.