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. 
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. 
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Leaks
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.
Substrates
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.
Membranes
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.
Grout
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.
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.
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.
Hi, Roger: Please help. I am building a tile shower, 3′ X 4′. I built the pre-slope with Mark-E goof proof kit sticks and Quikrete Sand/Topping Mix. The pre-slope dried for six months before I got back to it. I installed the liner earlier this week and leak-tested it. It held water to within 1/4″ of the two by four curb, but when I drained it, small puddles of water remain. Not deep, but I wonder if this will encourage mold. The crimps in the liner where it was folded up in the box will not flatten out, and act as water dams. The addition of the drain clamping ring affected the drain slope as well, because the bubble on my small torpedo level is centered now when placed on the slope and ring. I used DAP Alex Plus Clear Acrylic Latex Caulk Plus Silicone to seal the liner to the lower drain. I used no caulk on top of the liner. Is it time to start over? Thanks!
Hi Eric,
I would remove that liner and either get the stuff that’s on the roll (not folded) or go with a topical membrane. Normally the top mud deck will flatten out the creases, but there is no way to truly verify that since you have deck mud over it.
When you do that make sure you use 100% silicone around your drain (under the liner) and not latex caulk.
Hi Roger,
I am using a Kerdi Drain and Kerdi shower pan for a Shower Install.
I have decided to use Denshield for the walls surrounding it.
Denshield site shows a 1/8 gap between the bottom of the denshield and the shower base.
However….. I am perplexed leaving any space if I want to water proof it I know caulking will go in that space but what if the caulking fails?
Would it be ok to caulk along the shower base, set the Denshield into the Caulking, adhere the densield to the studs, then at that corner where the denshield meets the shower base use an alkali resistant reinforcment fabric with redguard and completely make that whole seem 100 percent waterproof…..
Could I not do it that way?
Thanks again for your imput.
I appreciate that.
Troy
Hi Troy,
Yes, you can do it that way. It will work just fine.
I will be installing a travertine decorative accent in my shower wall. Should I apply the sealer before installing or after grouting?
Your books have been a great help and I have learned a few things even after doing a several tile projects.
Hi Doug,
If your grout is darker than your travertine then seal first. It’s not necessary with lighter grout. It never hurts, though. It makes grout cleanup easier.
Hi, I just purchased your 3 pack for doing shower. It covers everything for the shower that you build a floor but nothing about doing with a shower pan and how to tie in backerboard to it and fill seems, silicone ext.
I thought that that would cover all and it didnt. please help. I have learned a lot so far but, already have shower pan in place and dont want to screw up. So would like to know where to go with tying in backerboard to pan.
Thanks
Hi Doug,
If it is an acrylic pan then you need the walls around a tub or pre-formed base manual rather than the one with the shower floor included. Send me an email at Roger@FloorElf.com and let me know which one you need (your waterproofing method) and I’ll email you the correct manual back.
Hi Roger,
Just looked at a friends new shower build. Dura rock cement board all hung, pre slope done. All seams on cement board were taped with regular drywall mud. Will he be ok red guarding over everything and the tiling ?
Thanks Steve
Hi Steve,
No, he needs to either remove the drywall mud and replace it with thinset or completely skim over the drywall mud with thinset before installing the redgard.
I am replacing a shower pan that has a center drain with a tile floor and a linear drain at the end. How do I get the rail that the shower door slides on installed?
Hi Charlie,
Normally with silicone.
Roger,
I forgot… it’s a tub/ shower combo and, I meant between the redgard and tile, not in the wonderboard. I’m 65, these things happen…
Greg
Same answer.
Hi Roger,
I just replaced a bathtub in an alcove after demo of the existing tile . it was good work on a floated mud bed, but my wife didn’t like it…I put in 1/2 inch wonderboard, taped the seams with alkali resistant tape & thinset before I Redgarded the whole thing. Since I left about a 3/16 gap between the tub flange and the wonderboard which I filled with silicone caulk, it strikes me that if any water gets into the wonderboard, it will be trapped by the caulk between my new tile and the tub. Most tub installation manuals show it done in this manner, but it would seem weep holes at the tile /caulk junction are in order. Would this cause mold, be a mistake, etc?
Thanks, Greg
Hi Greg,
You’re correct. Weep holes in tile installations
Hey Roger. Really cool of you to do this.
Question: If I just set my tub perfectly level, do you absolutely have to use a ledger when doing subway tile on the surround?
Thanks again.
Hi Dan,
Nope, if it’s level you can just start right on the tub.
Thanks, my man.
How do I inspect my contractors work? I feel so far that not every tile on my floor is level. Lines don’t matchup. This is on my bathtub, floor, wall. Tile on wall is uneven. cuts aren’t the same down the wall it looks choppy. I spent over 5,000 on tile and I think it looks like shit. I am addressing this tomorrow. Is there a right way and what do I say to him to fix it. Please help me.
Hi Chris,
I really can’t tell you how to talk to your particular contractor. Your best bet is to simply sit down and talk with him, bring up your concerns and ask him what needs to be done to get it fixed. Tell him you are unhappy with the way it’s looking and it is not at all what you had envisioned. Most of the time if your contractor is reasonable a solution can be reached. If he is not it will come down to what type of contract you have with him.
Hello Sir-
I am writing is response the substrate section. I am using a Dens-shield substrate in my 3 X 5 shower that is just surrounding a tub. Do I need to have a membrane behind that? I was confused if that was just for the Cement boards style substrates…
Also, I hear to leave a 1/5 inch gap between the tub and the substrate to keep wicking to a minimum. G/P (denshileld website) said a minimum of 1/8 inch. But a co-worker recommended 1/5. What do you recommend? I have only hung two sheets so it will be easy enough to redo.
Hi Ray,
No membrane needed with densshield. Leave 1/8″ gap, densshield does not wick water.
Hi Roger-
Thanks for the site – it is a great learning experience. I am almost ready to install 4×4 travertine tiles in our shower. I have read as much as I could find here but still have the following questions:
1. I bought the Custom Premium Medium Bed Mortar (because it says it is for marble, granite and travertine) before I realized the medium bed is for larger tiles. What mortar do you recommend for travertine this size (do I need anything special for travertine in a shower) and what do you think about this product in general (I know you say their MasterBlend is terrible)?
2. Would it cause problems to use medium bed on smaller tiles and is one easier to work with than the other (medium bed vs. thinset)?
Thanks.
Hi Zeke,
The medium bed mortar is just fine for your tile. It is a good product.
Hey Roger. First, thanks for all of your information. I just got and read 3 of your books. These have helped give me the courage to gut my bathroom. I figured I couldn’t do any worse than the builders did. I have demolished my shower which is recessed into the slab. There was no liner, and no liquid membrane in the shower, no wonder I had serious mold issues. In my haste, with the demolition hammer, I went beneath the mud bed ,for about 2 square feet, and to the bottom of the slab(3-4 inches deep). I found a liner at the bottom of the slab with the ground beneath it. I know this as I apparently cut the liner in about 3 spots with the demo hammer. . What would you suggest about fixing the liner under the slab, or is it even needed if I topcoat the poured shower pan.
Hi Scott,
That ‘liner’ is for the slab itself, to keep moisture from migrating up, not down. It should be fine if you fill it in and build your floor above it.
My house was built in 1941 it has plaster board ⅜ drywall type material it has what looks like a celotex outer sheeting then a wood lap siding and vinyl siding over that before the vinyl was installed there was holes drilled and spray fiber insulation was put into the stud cavity’s my question with vapor barriers and vapor retarders one breaths one doesn’t if I put a vapor barrier up am I going to have a case of double vapor and trap the moisture in the wall there is so many different ideals about insulating and cold and hot climates im in the middle of zone 5 and 6 between cold and very cold upper part of indiana seal all
Penetrations cracks water and air and would I be better off removing all of the plaster and replace with greenboard and duration rock or is plaster a good seal and moisture resistant substraight
Hi Rich,
I assume you’re thinking about a barrier such as hydroban, redgard or kerdi – correct? If so you can use the kerdi, but the liquid membranes need to be installed over a backer. The answer to your question is no, you will not be creating a double barrier which will trap moisture, you have space in the wall cavity where it can dissipate. The issue with a double barrier is having it directly on each side of a substrate – touching. Such as a vapor barrier behind a backer and a topical barrier over it, the backer is trapped with no moisture dissipation possible.
Hello Roger,
Im making a tiny bath larger for my handicapped Mother in my house. Im purchasing a threshold free shower and need to know what I need to put down on the rest of the bathroom floor before the tile.
Thank you for this site and the hard work it takes to help all of us clueless people,
April
Hi April,
It depends on what particular threshold free shower you’re using. It may be fine to use ditra or cement board, but your shower may require something specific.
Roger,
The mozaic tiles on our pool steps are coming off. Is there a clear waterproof sealant I can put over the tiles to keep them in place?
Thanks, Sue
Hi Sue,
No. Tiles are bonded from the bottom to the substrate, nothing you put over the top of it will fix it.
Hi Roger
My helper left an area about one inch or so away from the drain that he didn’t grout! We used laticrete epoxy grout. I’ve decided to bite the bullet and use the verrrrrry tiny amount of an expensive new box of grout to fill it in. Argh.
But do I grout right up against the metal drain? Will the epoxy adhere to the chrome drain cover so I can’t ever remove it to clean out the drain?
Also, am I correct in understanding that I should silicone the gap between the wall tiles and the floor tiles? It’s a presloped mud bed floor made with your generous online guidance by the way. I bought your book, but it was on the laptop that died, so I just wanted to verify that leaving a gap at the bottom of the backer is right (no silicone at the bottom), but now that it is tiled, I should silicone the bottom corner with the other changes in plane. Right?
Thanks Roger!
Hi Joel,
Epoxy will bond to a chrome drain. However, there should be a frame of some sort around the drain cover between anything you grout and the cover. The cover should remain removable. You did not say what particular type of drain you have.
Yes, silicone between the floor and wall tiles, as well as all changes of plane.
I have a walk in shower, water holds in a couple corners of the shower for hours after someone is done. Anyway to fix this? Thanks so much!
Hi Amy,
The only way to fix that is to replace the shower floor with one that is properly sloped.
I have been reading a lot on your site. I have a few questions about my tub tile that I am installing. I am nervous about installing 18″ travertine on my tub/shower walls. I have already installed the drywall and I am about to install the Kerdi. The walls at this point are within 1/8″ over a 5 foot distance. I am thinking about having 4 18″ tiles high and an accent strip that is about 3 7/8 inch. What trowel should I use to install the 18″ tiles over the Kerdi? I know Kerdi states to use unmodified thinset between Kerdi and travertine, is this advise or should I use modified for the 18″ tiles. Is it a good idea for a novice to try 18″ travertine on tub walls? Should I use a ledger board an start with the second row? How much space should I leave for caulk between tub and tile? Can I budget for a full size tile for the bottom row under the ledger board? Is this a good idea? Thank in advance for the help.
Hi Travis,
Unmodified is just fine on shower walls, no matter the size of tile. I would use a 7/16″ or comparable trowel for your tile. You’ll be fine with 18″ tiles – one square foot of 18″ tile weighs the same as one square foot of 12″ tile. If your tub is level you can begin with the bottom row or plan for a full tile beneath your ledger board. If it isn’t level use a ledger board and cut to fit the bottom row. I leave about 1/16″ for silicone.
Rodger,
Thank you for the reply and help. I am almost done with the travertine tub wall install. I have already bought a bottle of the 511 seal and enhance Miracle Sealant that I have read you recommend. What do you recommend to do following a finished install? Is there a good way to lightly polish the travertine, is this necessary? Or what is the best way to just clean it to get all random thinset etc off? Should I seal then grout? Or grout then seal?
Polishing the travertine isn’t really necessary, just clean it really well first with a damp microfiber cloth. You can seal it whenever. If you do it before grout your grout will not be sealed, if you do it after it will.
This is maybe an easy yes but has anyone ever used this kerdi product on a skylite curb? I’ve seen something that looks alot like it
Hi Richard,
Maybe. I have no idea.
Hi Roger,
I am using Kerdi boards to build a walk-in a shower. The local hardware stores do not stock Kerdi Fix caulk – What product would your recommend to seal inside corners?
Best regards,
D
Hi Don,
Kerdi-band is what is required to seal the inside corners. You can also use sika-flex instead of kerdi-fix. It’s in the concrete section of HD.
Hello, and Thank you in advance… (I Hope) We have problem!
So we have a new drop-in acrylic oval tub, that our contractor framed, mounted and cemented in, ready for us to tile. He told us that he would leave enough room for 1/4″ cement board and tile to go under the lip of the tub, the edge of which we will then seal with a 100% silicone sealer…
But, we have just realized that with the addition of thinset, there is not enough room, bugger! We could kinda force it, by pulling up the edge of the tub, but this seems like it could add unnatural pressure on the tub edge.
We will not have a shower in there, and there should not be a lot of water on the tiles…
I am at a bit of a loss, as I would obviously prefer not to take the whole frame apart.. Any inspiration?
Hi Tamar,
Get some ditra and use it in place of the 1/4″ backer. It’s thinner and you should have enough room to have it and the tile under the lip of the tub.
Great! Thank you so much, and sorry, but I have one more question that everyone is telling me different things about. In the above situation would you waterproof under the tile? There is no way for the water that could get on the tiles to drain into the tub, So my concern in regards to waterproofing would be that the water would end up pooling at the lowest point of the tub deck..If it is not waterproof the small amount of water that splashes onto the deck would have a chance to evaporate…But I don’t know? Thank you again!
It’s not required but it never hurts. And ditra is waterproof anyway.
Rough framing;
I know its going tobe the type of tile that I use the substrate thickness the thickness of the tile the thickness of the thinset, what im getting at is if I used 12×12 tile for my shower walls 36″x 72″ finished size. ½”backer bd plus ¼”thinset plus ¼”tile and reading you prefer chalk at all changes of plain so ⅛” at the vertical corners and at the shower floor and to end up with 3 full tiles wide and 6 full tiles long I would rough frame 38¼” wide x74¼” long am I on the right track or is this all wrong.
Its always a good ideal to talk to a pro and from What I’ve read it sounds like you’ve been doing this for a long time I search your sight for this answer but found none I hope its not a dumb question
Hey Richard,
Sure you’re on the right track – it your tiles are actually 12×12, which they won’t be. 12×12 tiles are normally ‘nominally’ sized, which means that the size of the tile plus whatever number the manufacturer pulls out of their ass for a spacing size, equals 12″. That could be 11 7/8″ down to 11 1/4″. Build your shower to the size you want it and cut the tile to fit into it.
Hello Roger!
I have a question regarding built-up shower curbs with (3) 2×4’s. I’m using the Schluter foam shower pan with kerdi. Do I cover the 2×4’s with cement backer board prior to the Kerdi or just use drywall over the top of the 2×4’s? Just wondering how the Floor Elf builds a curb with 2×4’s and Kerdi.
Thanks much,
Alan
Hi Alan,
You need to have cement board (best) or drywall (acceptable) over the 2×4’s, then kerdi. I currently do it with 2×4’s and kerdi-board.
I’m trying to re-tile my shower with porcelain tile, but it keeps sliding down the thinset. Any tips?
Hi Ellen,
Yes, begin at the bottom and work your way up supporting each tile with spacers between it and the tile below it.