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

  • Sharon

    Brand new house. Was leery of tiled shower due to issues at a previous house, but caved. Grout near fiberglass pan is flaking off in one section (12″x12″ tiles) and I’m seeing those dreaded moisture gnats! Still under warranty with builder, but how to get them to take action? Also, could the grout and gnats *not* mean a leak?

    • Roger

      Hi Sharon,

      It could just mean that water is being retained behind the tile. Is there silicone or grout between the tile and fiberglass? I would begin by calling them and explaining the problem.

      • Sharon

        Grout. I have them coming to look at it, but want to be educated so they don’t blow me off. :lol2:

        • Roger

          It should be silicone at any change of plane and between tile and a different material, both of which that junction is. That is why it’s cracking, the fiberglass (acrylic) expands and contracts at different rates than the tile and grout. Does it have weep holes?

  • Victor perez

    Hi Roger,
    I have a mold problem directly on the membrane between the cement backerboard. The bathroom was installed with a membrane then cement board then tile. I think someone made a boo boo. Now I have to clean it up. Since the liner has been compromised I think I may have to gut out the complete shower. I’m hoping to keep the floor which looks good.
    Please share your thoughts.
    Thanks. :rockon:

    • Roger

      Hi Victor,

      Unfortunately, if you have mold on the face of the barrier it will need to be replaced. That will require replacing the walls. However, you should be able to just remove the walls and lap the new barrier over the floor membrane without removing the floor.

      • Victor perez

        Hey, you are the man! 8) or elf!
        Did anyone ever tell you that?!… ok so I found out Mickey mouse still exists. Pun intended. There was a liner installed only about a foot over the floor.
        2nd problem: There is mold everywhere!
        Mold on the liner in between the tile on the floor and sub floor. I was hoping to go with your initial advice and keep the tile on the floor. My question is how I you determine if I have to dig out the sub floor due to present mold? Can I just spray a mold remediator and place a dehumidifier over night to try and save this mess.
        Thanks again brudder.

        • Roger

          The ONLY thing that will kill mold is completely drying it out. Even doing that, unless you remove the spores after it dries out, reintroduction of moisture will begin to feed the mold again. Unfortunately if you have mold down there the best course of action would be to strip it all down and start again with a properly build shower. I know it sucks – I do it every day. :D

          • Victor perez

            Ok last question and thank you from all of us on this blog, for taking time out to answer our questions.
            Do you recommend the schluter kerdi shower kit?
            Thanks again.

            • Roger

              Yes, it’s a quicker and easier way to waterproof your shower. I prefer to mud my pans rather than using the base, but that’s mostly because my showers are rarely standard sizes.

  • John

    Hi Roger, tiling a shower, is it good to install 3/4 TG advantech to studs first, then hardy board and tile?

    • Roger

      Hi John,

      No, you do not want any sort of plywood behind your shower wall. Just the backer and tile (with correct waterproofing, of course).

  • Roger

    Hi Garth,

    Yes, you can.

  • Mark

    Hi Roger,

    Very nice of you to answer questions. Much appreciated.

    I have a new construction home and my tile shower has issues. The edge where the floor and wall meet takes many days to fully dry after a shower (3-5 days). If I go away for a few days and return, just that seam will be wet. I’m quite concerned that there are pockets of water being trapped behind the tile, which will lead to mold.

    The original installer is working on this, but seems clueless. I think his plan is to re-caulk and re-grout just the seam.

    Questions 1) Do you have any theories as to what might be the cause or causes?

    Question 2) Is there more that should be done beyond grout and caulk? These are porous materials, so while caulk and grout might help, it doesn’t seem to address the root cause, and still may be a long term headache.

    Question 3) If this isn’t resolved well, beyond the unpleasant appearance of mold, can unseen dangerous mold grow?

    Any advice you can offer is much appreciated!


  • Bob

    Hi Roger,
    Any reason to use silicone at base of tiled wall to tiled shower floor instead of grout as I have used Redgard over a mud pan up about 8″ on the
    Hardi board walls. The corners were mesh taped with thinset before using Redgard. Thanks for your advice.

  • Alvin

    We have a travertine shower which is 10 feet long and 5 feet wide with curbless entry at end opposite 4 foot trough drain. I do not know base construction materials; however shower is build over wood floor construction (crawl space) and 2×4 walls. I have a couple of issues.

    1) The shower wall tiles extend past the shower floor tile. Is this a proper installation method as the change in plane joint is exposed to direct water pressure when shower is in use? Seems joint would be much longer lasting if floor tiles extended below wall tiles. The original grout at this change in plane joint cracked after a year and was replaced with Latasil. Now 2 years later the Latisil has started to pull away from shower walls. Would epoxy grout at this change in plane joint be an appropriate PERMANENT repair? Can I use epoxy grout just in the transition joint and not regrout entire floor?

    2) After entering the shower and turning to the right so your back is against front 5 foot wall and 4 foot trough drain is located at opposite end of 10 foot shower length there is an area just in front of the right side of the trough drain which holds water. Estimate size of area to be one square foot. How can I repair this issue?

    3) One last question – how can I determine if weep holes are working properly at trough drain? It has a single drain located at center of the trough.

    THANK YOU in advance.

    • Roger

      Hi Alvin,

      1. Silicone is not a permanent product, it will require replacement periodically. It’s simply a maintenance issue. Epoxy MAY work there, it may not, it depends on the construction of your shower. You can use it just there, but you’ll always notice the difference.

      2. The only way to repair that is to properly redo the slope beneath the tile.

      3. Linear drains do not have weep holes.

  • Scott

    Some spelling errors on that thanks to my smartphone. What should I fill the gaps with before applying the thinset*

    • Roger

      Hi Scott,

      You should tape and mud those areas with alkali-resistant mesh tape and thinset (filling the gaps as you do that).

  • Scott

    Hi Roger,

    I decided to retile my shower myself (probably wasn’t the best idea). I am worried about waterproofing it correctly. I put plastic tyvek sheet between the framework and the substrate. I havery gaps between a few places the cement backer board didn’t line up fully. What should I fill that with before I put the subset on?

  • Brandon

    Hey Roger – I just bought a newer home and it seems like the plastic shower pan, with built in weep holes is allowing water to go inside the weep hole, and then run along the length of the built in tile flange up to the front of the flange/shower pan where it meets the drywall. It’s not leaking much though. Any suggestion on how to stop that? Can i put in some sort of stopper to keep the water from draining that direction? thanks!

  • Lyn

    Roger, you are great! Love your details and information with answers to the questions. My mom has a tiled and grouted guest bath shower stall that leaks water out onto the floor when in use, from either the glass slider door sill on the 4″ tiled rise into the stall and/or also from the outer corner where the plumbing hardware wall and rise meet at the floor corner. Every time the shower is used, a pool of water forms along the outside of the rise from the back wall by toilet to almost 3′ along the rise towards the opposite wall. The leakage pool is minimal, about .25″ deep by 5″ wide…enough to make a mess and require mopping. So, rip up the shower? Caulk? Money is tight, but it needs to be fixed right. Ideas please?

  • Lee

    I love your site Roger.

    I am redoing a basement bathroom in the kids’ house.

    Can I attach cement backer board over foam board in a shower? It will be tiled with porcelain. There is a block foundation 2×4 treated wall with foam board on the inside. I am concerned the screws would not have enough support going through the foam. Would adding adhesive help. (what kind?)

    Many thanks,

  • Paul Cotugno

    Bought a new house. In the Guest Bathroom shower stall, I noticed that the imitation marble walls did not extend sufficiently downward even to butt with the lip of the Pan…..leaving a gap of approx 1/8 of an inch between the base of the walls and the lip of the pan. There being no way that caulking could waterproof the gap – which is continuous along both such wall sections – all I can think of is a sort of “skirt”, which would overlay the entire lengths of the bottom seams….attaching to both the base of the wall and the upper portion of the lip of the pan.
    Or ain’t there any such thing available?

  • Cole Shelton

    Hi Roger,

    I used Redguard on our tub surround and am almost done with the tile. I caulked underneath the backerboard, but was wonder should I caulk under the tile as well?

    Thanks for the site, it’s wonderful!

    • Roger

      Hi Cole,

      What do you mean by ‘caulk under the tile’? You should caulk or silicone all changes of plane, like where the wall tile meet the tub, but you need to leave weep holes.

  • John Walls

    CAULK—Regarding using silicone caulk in showers (for tile or substrate like Hardi):
    There seem to be a lot of “silicone” choices these days. For example, G.E. offers SI (the old original stuff), SII, and “Supreme”–each one with a higher price and supposedly better properties than the last. And then there’s the Kitchen and Bath versions (mold killers, I guess).
    1) When you talk about silicone in your eBooks and posts, are you referring to the old original stuff with the vinegar smell?
    2) In your experience, is it worth the upgrade? Costs more, but you don’t use a lot of it.
    3) What’s your opinion about using Polyurethane caulk (like NP-1) for showers?

    • Roger

      100% silicone is 100% silicone. They can advertise anything they want on it – but it’s all comparable as far as I’m concerned. Never used the polyurethane, probably because I use silicone and it works well for me – no reason to change.

  • Tony

    Hello Roger, thanks for creating this site, extremely useful. Can I tile directly over a concrete basement floor for a shower if I coat it with Redgard, without pouring deck mud or using a liner.
    Thanks, Tony.

    • J

      Hi Tony,

      I think most would advise against this practice (skipping a liner or poured pan, or fiberglass pain). I would not pass your local/state/national building codes (even if inspection is not being done), and could cause real problems with no place to “catch” your water on the floor basin.

    • Roger

      Hi Tony,

      You can, if it’s sloped and you are able to tie the waterproofing into the drain correctly. A mud deck is a MUCH better option.

  • jen

    I had a new travertine custom shower built
    It has a bench across the back. My understanding is that it’s a plywood box covered with a membrane covered with tile
    It’s been a year and I discovered the bench is leaking into the wall. I opened an access panel in the wall so I could see under the bench. I used a fungicide to protect against mold and a dehumidifier to dry everything out. Now I’m trying to figure out how to stop the water. Will a bead of silicone caulk be sufficient or do I have to rip out the shower??

    • Roger

      Hi Jen,

      No, silicone will not do it. The bench will need to be rebuilt.

  • Dana

    Hi. We are finishing our basement and want to put a bathroom with a tub that will act as a shower as well. The problem is the tub Will be against an outside wall/ foundation(about 5 ft underground, 2 ft above ground). When it rains REALLY bad there’s some seepage on that wall. We want to waterproof it before installing the tub. At this point there’s no framing and we just dug and installed the rough Plumbing as well as drain tile at the bottom of the wall. But we are still concerned and were thinking to put shower pan liner on the wall before we pour the cement over the floor piping. The liner would come against the wall and end in the ground by the drain tile with cement over its bottom end. Then would come the framing, durok, tub and tile.
    My husband is concerned if this arrangement might dresser sweat and cause mold.
    Is the shower pan liner a good idea or we should use something else? Should we put insulation in between the studs under the durock?
    Thank you.

    • Roger

      Hi Dana,

      You have negative hydrostatic pressure on that wall, you need to address that before anything else. A rubber liner is not a good solution, that moisture has to go somewhere and trapping it under a liner may cause larger problems. We don’t have that type of problem around here, so I really don’t know how to solve that. I’m sure google can point you in the right direction.

  • Bryce F Bailey

    Hi Roger, When tiling a shower, will changing grout color between walls and floor cause an issue down the road? Also, while I have your ear. Whats the proper sequence? Walls or floor first, as far as laying and grouting.

    • Roger

      Hi Bryce,

      No, it won’t create any problems at all. I normally do floors first, but either way works fine in a properly waterproofed shower.

  • Thomas

    Hi Roger, I have a white tiled wall shower with an acrylic base with upstand. The walls have a complete waterproof membrane, the tiles are grouted with epoxy grout and the line where the shower tray meets the first row of tiles has been siliconed. After first 2 weeks fuse, the bottom row of my white tiles have gone grey (suggesting they are wet). We replaced the shower assuming the tiles were faulty….the new tiled wall (using different tiles, but still in white) has done the same thing. Any advice you can offer to solve our dilemma? Many thanks in advance!

  • tom

    roger, the line right above the shower pan, should that be grouted or caulked or just left open since there is a lip on the shower pan..

    • Roger

      Hi Tom,

      It can be siliconed or left open.

  • Chris

    Roger I’m tiling a sloping wall in my bathroom, does the same technique as tiling a ceiling apply ?

    • Roger

      Hi Chris,

      Not normally, you can just start it at the bottom and stack them. Unless you have a more than 60 degree angle or so you don’t need to use the bulls-eye.

  • Matt

    I’m in the home strech of my first shower install. I bought the kerdi shower kit and have used kerabond. The floor is a basement slab with kerdi shower tray on top followed by the membrane. When the membrane was finished, I placed cardboard over the floor to protect it. I installed the wall tiles and then had quite the adventure with the ceiling tiles. I tried the suction trick but 2 tiles still fell (one almost knocked me out)! I finally got the ceiling done. That was a month ago. So tonight I removed the cardboard from the shower floor (and all the mess of dried thinset droppings) so I could start laying the mosiac floor. To my horror, I discovered that when the 2 ceiling tiles fell (they were heavy 24 x 12s), the corners had pierced the cardboard and the membrane and left a hole/slash in the shower tray. Yikes. So I know the fix for the membrane is to just use some kerdi band attached over the hole, but how do fill the hole in the styrofoam tray? Since its eps, it cut the foam and compressed it into a hole about 4 in x 1/2 in. Is expanding construction foam the way to go to fill the hole? Or something else?

    Also, once the hole is filled and I cover with kerdi band, do I use thinset to attach the kerdiband with kerdi-fix? Since the repair membrane will sit over the breach, I’m concerned water could leak through the thinset. Or will the thinset seal the new kerdiband patch effectively?

    Thanks in advance Roger!!

    • Roger

      Hi Matt,

      Fill the hole with thinset, place a kerdi-band patch over it with thinset, then let it cure. It’ll be watertight.

  • Page Lewis

    sorry. Will new bottom bypass pan and drain directly into DRAIN?

    • Roger

      It will if you get a drain extender and tie it into the existing drain.

  • Page Lewis

    hi. I have a tiled shower with seat. No idea of wall construction behind it or of condition of pan. Underside in crawl space suggests leaks. Can I just get a fiberglass bottom installed after taking out some bottom tiles and avoid taking out pan. Won’t the new bottom bypass the pan and drain directly into pan? Thx.

    • Roger

      Hi Page,

      I’m unsure what you mean by a ‘fiberglass bottom’? Do you mean an acrylic shower pan? If so, it likely won’t work as well as you need because your bench still needs to be inside the pan, which is likely where your leak derives.

      • J

        Hi Page,

        You’d need to remove the bench first, and likely could not replace the bench on a store bough acrylic “fiberglass” shower pan. There would be no way to attach the bench w/o putting holes through the pan (more leaks).

        You might correct the source of leaks (use water proofing menbrane if you can find it by running the water for a bit, and leave all alone.