I get a LOT of questions from my readers about basic shower construction. I understand that my readers don’t consider this stuff basic and there’s no problem with that. The problem is that I end up answering the same questions over and over and over… So, to save what very little is left of my sanity (which is a number roughly equivalent to absolute zero) I will cover some basic things here so I can simply reply ‘read this’.

If you’ve been channeled to this page by one of my smart-ass comments please take no offense to it, I’m here to help. Please understand that I currently have over 12,000 comments (questions) on this site (seriously) which I’ve answered – every one of them. I’m just trying to make your life (mine) easier.  I will continue to answer every question I’m asked, I’m just super cool like that. 8) If, after reading through this, you still have questions feel free to ask them in the comments below.

You can also download my shower waterproofing manual which should answer a lot of questions and cover basic techniques and methods you may be confused about. Go ahead, it’s free.  So without further ado (doesn’t even look like a word, does it?) let’s get on with it. (For all my readers who feel the need to correct me: I KNOW it’s actually ‘adieu’ – I was being facetious. Thanks. :D )


First and foremost – tile is not waterproof. Grout is not waterproof. Adding sealer to your tile or stone will not make it waterproof. Your shower should be completely waterproof before a box of tile is even opened! No matter which waterproofing method you choose, proper substrate preparation is the only thing that will make your shower waterproof.

If you have a leak in your shower – stop using it immediately if at all possible. If that is not possible (it’s your only shower) have the shower repaired – immediately. If you see water leaking it is likely not nearly as much water as you don’t see leaking into your wall cavity and structural framing. By the time you ‘see’ most leaks the framing is normally already considerably compromised.

No, there is nothing you can put over your tile to make your shower waterproof if you have a leak – not even sealer. A tile or stone sealer is made to make your tile and grout stain-resistant, not waterproof. It does this by sealing the pores of the tile and stone to slow (NOT STOP) the absorption of liquid and prevent staining. It only means you have more time to clean up the spilled red wine cherry kool-aid before it stains anything.


Drywall is not an acceptable substrate for your shower unless you are using Schluter Kerdi waterproofing membrane – that’s it. Cement backerboards are the standard and there are also other products such as waterproofed, gypsum based boards like Denshield and waterproofed, foam-based sheets like wedi or kerdi board.

Cement backerboards are not waterproof. They are water stable, which simply means that they will not swell or disintegrate when exposed to moisture or water – they won’t change size. But they are just like your driveway, they will soak in water, hold water, and dry out, just like your driveway when it rains. If using backerboards there needs to be a waterproof membrane utilized as well.


If you are using a topical waterproofing membrane such as a liquid like redgard or hydroban, or a sheet like kerdi, do not use a moisture or vapor barrier behind your substrate. If you have a vapor or moisture barrier behind your substrate do not use a topical membrane on the front of it. This combination creates two waterproof barriers with your substrate sandwiched between them. any vapor or moisture trapped between them has absolutely no way to dissipate. This is lovingly referred to as a ‘mold sandwich’. It is not tasty. Use either a moisture or vapor barrier behind your substrate or a topical membrane on the face of it. One or the other – never both.

With that said, if you want to use a topical liquid such as redgard on the seams of your backerboard, after you tape and mud them, you can do so without problems. If your moisture barrier and backerboards are properly installed there is no real reason to do so – but if it will help you sleep at night go ahead and do it.

If you are using a topical membrane and you have an exterior wall with either plastic facing or kraft paper facing you need to cut slits into that facing before installing your substrate. If you do not it will create the aforementioned mold sandwich. Give moisture or vapor somewhere to dissipate.

Shower-tub transitions

There should be a gap between your tub or acrylic shower base and the bottom of your backerboard. If you are using a traditional barrier waterproofing method you do not need to do anything with this gap. Do not fill it with silicone! This will trap moisture running down your barrier and it will have nowhere to go. If you are using a topical method you can fill it with silicone if you want. If you are using liquid you should fill it with silicone. This creates a waterproof plane between your membrane and the tub or base so water or moisture ends up in the drain rather than in your wall.

When you tile you can tile right over that gap. You should not fill this gap with thinset behind the tile – it will crack due to movement. Your wall and tub or base will expand and contract at different rates – it will crack any cement-based product you place between the two. This includes thinset as well as grout. You do not need a solid backing behind your tile over this gap – it should be less than 1″ wide. You shouldn’t normally be walking on that tile in that particular spot. Yes, it can just hang there.


If your grout is cracking it is due to movement 99.9% of the time. Type ‘cracking’ into the search box up there and you’ll find in-depth explanations for your viewing pleasure.

If you have white, or lighter than normal grout when you’re finished grouting it may be efflorescence. This is mainly due to minerals in the water being left on the surface of the grout when the water evaporates. It is usually indicative of either incorrectly mixed grout or using too much water while cleaning the grout – not wringing out your sponge enough. This is normally only on the surface of your grout. Scratch the very top layer of your grout in an inconspicuous spot with your fingernail. If you have the correct, or at least a darker, color beneath the surface that is the likely cause. The easiest, quickest fix, provided it is only the very top layer, is to get some drywall sanding sponges and go over the grout lines very lightly. Just like burnt toast – scrape it to the color you like.

Corners and changes-of-plane

Caulk. :D

Disagree with me?

Like any other website I get my fair share of people who disagree with my methods or techniques – it really doesn’t bother me. I am more than willing to have a civilized, intelligent conversation about anything tile related. If, however, you simply attack me personally and act like an uncivilized ass I will call you on it – and not in a nice way. I write this blog in a particular manner, it does not mean that I take my profession lightly – I most certainly do not. If I wanted to be a pompous bastard I currently have 19 letters I can place after my name – all tile related. But I’m not a pompous bastard – you can just call me Roger. :D

If you are a contractor with a customer who has come here for information and I’ve told them you’re wrong – realize that the extent of my knowledge of that particular project is limited to what I’m told by your customer. It does not mean that I am ‘out to get you’ or anything of the sort. I normally limit my replies to those situations by stating the current TCNA and/or ANSI standards pertaining to what I’m told. If you disagree – please let me know in a civil manner, If you’re correct I’ll back it up – I do this everyday, too! If you’re an asshole about it expect the same in return (It’s the comment by ‘Kanela’ with the bold print before it) – and please have a thesaurus handy to interpret my reply – I’m a very well educated asshole.

That’s it for now. I will likely add to this post on a regular basis. If there is anything I’ve caused confusion with please, for the love of God, let me know. I can change this page since, you know, it’s my website and all. If you have any questions at all please ask them below – I’ll answer, really. :D

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Leave a Comment

  • Aaron

    Wow, just found your site and love the information! That said I apologize if you’ve already answered this question and I haven’t stumbled onto it yet…hopefully my dog doesn’t catch on fire for asking ?

    I’m installing a tile shower wall and the mrs would like an inset on an exterior house wall. Is this okay to do? If so, how should I navigate the insulation in that area??

    Thanks for the help, and the great site!

    • Roger

      Hi Aaron,

      It really depends on the weather in your location. If you get freezing temperatures you CAN put it on an outside wall, but it’s not really the best bet. Depending on how deep your exterior wall cavity is, and how deep you want your niche, you can either cut the insulation and move it to the top and bottom of the niche (push it up and down to create space for the niche), or, if the cavity is deep enough, you can build the niche in front of the insulation by compressing it behind the niche.
      You can also use something like kerdi-board for the back of the niche, which does have an r-value (although very low), and that can at least add a little insulation behind the niche itself.

  • Robert

    Great site, filled with useful tips. One question, I’m building a walk-in shower but need to create a minimal curb to establish enough pitch to maintain proper drainage.

    I’m using the stucco base you recommended for the 2 3/4” step and it worked great, honestly better than my mud base, which has a few low spots that pool water. Can I use the stucco base to fill in these low spots, or should I use more dry pack, thinset, or “gulp” tear it all out and start my mud pan all over again?

    • Roger

      Hi Robert,

      You can level and smooth that out using thinset. The stucco or dry pack won’t bond correctly with just a really thin layer like that, but you can skim over the entire thing with thinset and get it all nice and even to fill those low spots.

  • Zach

    I have a question regarding my shower pan. I installed a vinyl pan liner w/ my mortar bed sloped on top of that. Should I put red guard on the top of my mortar prior to installing tile or is this not needed?

    Also, I left a gab between my cement board and pan. Would you recommend caulking that or mud it in w/ mesh prior to tile install

    • Roger

      Hi Zach,

      It is not needed and may actually cause problems down the road.

      You don’t need to do anything with that cap. Do not caulk it, that may trap water.

  • Allen

    Hi Roger,
    I am building a shower with per pitch, liner then pitch sand mix. I am installing duroroc on the walls. No vapor barrier behind boards. Should I redguard the drypack motor before tiling? And should I chulk the floor to wall tile seam

    • Roger

      Hi Allen,

      Why no barrier behind the durock? Are you using redgard OVER the durock? If so, then no, do not redgard the drypack before tiling, your floor is already waterproof. Do not caulk between the floor and wall tile, install mesh tape and mud to that transition, then paint the redgard down the wall, over that mesh and only about 2″ out onto the mud deck. DO NOT bury your durock in the mud, there needs to be a gap left between the bottom of the board and the mud deck.

      • Allen

        Hi Roger, I did red guard over the durock with 3 coats. I didn’t redguard the drypack bed like you suggest but I just laid the shower floor tile and I have the wall board about a 1/2″ above the tile. I just saw your response about using mesh at the bottom corners and red guarding. All I can do now is caulk the bottom transition I guess?

        • Roger

          Yes, just silicone that area and you should be fine.

  • Erik

    Hi Roger,
    I had a “pro” tile my shower and the floor to pan gap is almost 1/2”
    Trying to come up with a solution to this issue. Before I go too far down the trial and error / lather, rinse repeat path some suggestions are welcome.

    I’ve considered cleaning the mass of grout out that is shoved in the seam and installing some caulk rope. Then making a nice looking thick ass caulk joint (good luck) to just tiling over the pan tile with another layer to raise it and close the gap.

    Any suggestions?

    • Roger

      Hi Erik,

      Wow, ummm… :D

      I assume the bottom row of tile is not cut, correct? If it is you can replace that row with tiles cut correctly, but I’m assuming that isn’t an option. 1/2″ is HUGE. You can tile over the pan to raise it, pain in the ass but will likely have the best looking outcome. I’m hesitant to suggest the caulk – that always looks like shit. Is it consistent enough (the gap) to install some sort of liner or contrasting tile in there? That may be an option. I think raising the tile floor will give the best end result.

      • Erik Wittenzellner

        Yup, you echo my thoughts.

        I’m going to try something like putting in a thin strip before I go and tile over it.
        I’ve toyed with the idea of putting in a strip of stainless and grouting that in or a liner like you suggest.

        Having to fix the drain hole he hacked in with some antique Egyptian pyramid carving tools…
        Then on to the wall interface.

        I’ll get it.

        Thanks Roger

        This is a tile over tile job already so a 3’rd layer is something I’d prefer to avoid.

  • Lourdes Llaneza

    Hi Roger,

    Can I apply redgard on a Hardie backer board? If not, what is the best backerboard to use on my shower walls using redgard waterproofing membrane. Can I use redgard directly in between marble shower pan and or bathtub and backerboard with a space of 1/8. Thank you so much.

    • Roger

      Hi Lourdes,

      Yes, you can use redgard on hardibacker. I don’t know why you would want to use it BETWEEN the pan and backer? Can you explain that to me a bit more?

      • Lourdes Llaneza

        Hi Roger, so I put silicone on the backerboard- bathtub transition. As I mentioned, I redgarded the backerboard. Should I apply redgard top of the Silicon or just leave just like that and put the tiles on top of it? Thank you for your wit and your time.

        • Roger

          Aaah, I gotcha. I always tell people to go ahead and paint over the silicone. It will not bond – but what it does is fill any small areas or voids that may not be completely sealed.

  • Robert Walker

    Hi, Roger. Really appreciate your blog. Very informative. Just completed the prep work for my first shower enclosure, and having researched the project to death ahead of time, I did leave a 1-inch gap between the final mortar bed on the floor, and the bottom of the backerboard on the walls to prevent any wicking of moisture up the walls. But now that I’m about to lay my tiles, I’m wondering if that practice applies to pebble tiles as well as it does regular square tiles. I can see how leaving just the bottom inch of a 12-inch tile hanging off the bottom of the backerboard would work, but I’m not using standard tile. What am I going to do with that last row of pebbles above the floor? Aren’t they going to just flop around with nothing behind them for support? Can I perhaps mostly fill that 1-inch gap with another layer of two of pebbles laid flat on top of one another before leaving a smaller (say, 1/8 to 1/4 inch gap) between them and the bottom of the backerboard?

    • Roger

      Hi Robert,

      Do you mean you’re installing pebbles on the wall? If so you can extend that gap using mesh tape and thinset, let it cure, then tile over that. If pebbles on the wall is not what you’re doing – please let me know what you are doing. :)

      • Robert

        That’s exactly what I meant, Roger. Thanks for the prompt reply, and for the excellent suggestion. I don’t need to extend the walls much to bring the pebbles closer to the floor and still maintain a reasonable gap to prevent wicking. Back at it tomorrow! Thanks so much for all you do. For those of us laypersons just trying to muddle through, you’re a lifesaver!

  • Robert Palmer

    Roger thank you for your blog here, very informative. I am planning on doing my first shower install in our new pool house. I am building a 62×36 three side walk in shower with about a 30″ curb entry on a concrete subfloor. I am planning on doing a dry pack mortar sloped floor with rubber membrane 6-7″ up walls inbetween mortar layers with cement board walls. If I put the cement board walls in first and the mortar floor over them is it okay to use Redgard waterproofing mebrane over mesh tape at the joint where the cement board and mortar floor meet? And should the Redgard membrane be applied over the all cement board walls? Floor and walls will be finished with tile and grout and there are no exterior walls.

    • Roger

      Hi Robert,

      Once you get the preslope down, install your liner over it and up the walls, then you can put your cement board up before the top mud deck (I assume this is what you were asking…). Yes, you can redgard over the seam at the floor, and yes, you should install redgard over all the cement board if you don’t have a barrier behind it.

  • James

    Great website and guides, Roger. Wish I could pick your brain over a few beers sometime.

    I’m curious if your recommendation to silicone the tub to shower transition cbu to tub lip gap still stands? What is the lifespan of that silicone and it just seems like a bad idea if it’s not a long term seal because wouldn’t you need to demo the whole wall to replace it?

    Also, have you any updated information on sealing the shower cartridge cutout holes other than the damn of silicone placed on the backside of tile forming a ring around the hole?
    We want to use durock with redgard. No traditional vapor barrier.

    • Roger

      Hi James,

      If the silicone is not regularly exposed to open air, which that seal would not be, it will not lose elasticity and dry out. So the lifespan of it would be the lifespan of your entire installation (done properly – until you wanted to replace the tile). You can use the schluter valve seal (google it) around the cutouts if you want to. They can be used with redgard. It’s essentially the same thing, except it’s a ring of rubber rather than silicone.

  • Diana

    I just purchased the manual for Creating a Shower: liquid topical products. My question is: do I install the backer board and then the deck? The illustrations look like the deck goes all the way out to the studs and the backer board is sitting right over it. But I would imagine that to be a difficult way to make sure the sides and all are level and flat. Some of your pictures show the mud going in before the backer board, but I imagine that could be because they’re pictures of a different project and it’s the pre-slope and will have a top deck later on.

    I would think it would be easier to put in the mud deck, then the cement boards. If that is acceptable, do I install the backer board fairly close to the top the mud deck–say, similar spacing as is everywhere else for the boards? Or do I install the boards and then mud in the bottom of them with the deck?

    Thanks in advance for the clarification. Great site; I definitely enjoy your style of writing.

    • Roger

      Hi Diana,

      You can do it either way, but with a liquid waterproofing I find it much easier to install the walls first, then the deck mud directly against it. If you do it the other way you have to have the backer sitting directly against the mud in order to span the transition with the waterproofing, or you need to use something like kerdi-band to span it for the waterproofing.

      • Diana

        Thanks, Roger.
        I kept researching and found that most pictures showed the walls going up first, then the mud floor, then the topical product. But it’s nice to have confirmation.

        I have another question for you:
        I’m demo-ing my 3’x5′ shower to redo (had concerns that previous owners cut some corners). Last night I found the previous floor tiles underneath the newer floor tiles. All this inside what seems like a metal shower liner filled with way more sand than a 5:1 ratio. And to boot, this area is dropped lower than the rest of the concrete slab. Googling has not returned any assurances that this may be how homes were built in 1968. Any experience with an already-recessed shower floor on concrete?
        If it’s structurally okay (which I would assume it is…), then I may change my design plans to work with the lowered shower area and make it curbless. Definitely looks odd.

  • Aron

    I wish I had found your website sooner – it would have saved me many hours of watching YouTube videos. Some very good, but some a waste of time.
    My question is whether color matching silicone at changes of plane is enough superior to color matching siliconized acrylic to put up with the greater difficulties of applying 100 % silicone? I have a complicated tile installation using 3 different sizes of classic subway tiles plus pencil and mosaics. With many “crossing” grout lines when I will tool the caulk, I expect challenges producing a clean look with the silicone, despite having a Cramer Fugi Kit with the rails that are supposed to slide over the grout lines to produce a clean bead. I’m wondering what you think … 100% sili or siliconized acrylic? Thanks!

    • Roger

      Hi Aron,

      I would absolutely use the silicone. They will both lose elasticity over time and require being replaced, but the silicone will normally last about three times as long as the acrylic will.

  • Thuan Huynh

    Thank you for this article. This article save my butt. I only installed vapor barrier behind my cement board on the wall but was thinking about applying red guard to it as well but thank god I came across this article. Question though, I saw lots of youtube video on tiling their shower pan. But nothing mention about either leaving a 1/8 gap perimeter on the shower pan with grout or silicone. Another question which is prefer redguard or tradiation plastic barrier?

    • Roger

      Hi Thuan,

      TCA requires a gap at changes of plane which gets filled with a sealer (caulk or silicone). Youtube doesn’t always follow industry standards. :D Redgard, or any other topical membrane, is a better, more efficient system than a barrier since the waterproofing is directly behind the tile.

  • Ed Fortuna

    Hi , I have a question. I’m tiling my shower which has an acrylic base pan. Tiles are about 5 X 10 with 1/16 grout line . The hardi backer is 1/4 inch above the ledge of the pan. Do I leave a 1/4 inch gap with the tile too or tile lower closer to the pan? and do I caulk that gap after installing tile or leave open for drainage? I was also thinking of using GE 5200 Marine adhesive or GE Marine silicone instead of caulk if I’m supposed to caulk. The GE 5200 I’ve used on boats and it’s indestructible. I was thinking of no caulk at all too since caulk always seem to get moldy at some point . I would appreciate your thoughts. Thanks Ed

    • Roger

      Hi Ed,

      Go with a 1/16″ gap, and caulk or silicone it with weep holes. The reason it gets moldy is that NO ONE ever leaves weep holes and it traps water.

  • Greg

    I still struggle with the “mold sandwich” concept. If I put up a vapor barrier, CBU and a liquid membrane supposedly I have created the “sandwich”. But if water does make it past my tile and grout, won’t it evaporate back out the way it came in? Thanks.

    • Roger

      Hi Greg,

      Yes, the portion of water that is not being used up feeding mold will dissipate back out. :D