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 3000 comments (questions) on this site 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 – 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.
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Roger,
Not sure this question fits here, but how do you handle overlapping of floor (pan)/wall tile transition. In other words, do you prefer to have the wall tile edges abut (assuming a small expansion gap) the floor (pan) tile surface or have the floor (pan) tile edge abut the wall tile surface? I’m guessing it really doesn’t matter that much, but maybe one method hides goofs better(?)
Hey Don,
I prefer the wall tile over the floor tile, but it doesn’t make any difference from a waterproofing standpoint. It’s merely a personal preference. I just think it looks better.
Roger,
When you refer to the “lip” of the tub, are you referring to the flange that is attached to the wall (vertical) or the top of the tub (horizontal)? I’m slightly confused as to how much of a gap to leave between the top of the tub and the bottom of my substrate. I’m taking on my first tub enclosure and want to get it right the first time and not have to do it twice.
Thanks for your help and all the information on your blog!
Adrian
Hey Adrian,
It depends on where I referred to the lip. When referring to the tub and the lip it is the vertical portion of the tub. If shimming out the backer over the front of the lip then it would go 1/8″ above the horizontal portion. If not shimming it out it goes to about 1/16″ above the lip.
Hi Roger,
You mentioned there should be a gap between your tub and the bottom of your backerboard and furthermore, if using a topical method you mentioned to can fill the gap with silicone. Then you mentioned when it comes time to tile, you can tile right over that gap.
I am using a topical method (liquid membrane) and am using a tub base with tile and hardiebacker on the walls. The tub has a 1-2″ lip on 3 sides.
I was planning to slightly overlap the tub lip with backerboard. And then use silicone to cover the hardiebacker/tub lip transition. Next, I plan to apply the liquid membrane to the hardiebacker. Lastly, I plan to tile over the hardiebacker and tub lip all the way down to the tub, leaving 1/8″ gap between the tub base and tile, which will be filled in with silicone caulk.
Does that sound about right to you?
Thanks for your help here.
Chris
Hey Chris,
Yup, you have it all correct. Be sure to leave weep holes in the silicone between the tile and tub when you’re done.
Ok got it, forgot about weep holes, thanks!
Hi Roger,
My tub lip (1-2 inches high) is currently screwed into the 2×4′s, which seemed to have been part of the tub install. I am thinking I will need to waterproof over and around these screws, as I wasn’t planning to to cover the screws with the backer.
Have you run into this before or have any thoughts as to what I should use to put over/around the screws to make them waterproof. Tile will go over them, but as I learned tile isn’t waterproof
Thanks,
Chris
You can cover the heads of them with your liquid membrane. You can also cover them with just plain silicone. It is common practice to screw the tub flange into the studs.
I left 1/4″ gap between the tub deck and Hardi backer board edge, which overlaps the lip. My Redguard goes to the edge of the backer, but I haven’t silconed anything yet. Do I understand correctly that I should silicone between the tub and backer board before tiling (excluding the weep holes)? Then silicone again using the grout-matching caulk after the tile is in place?
Thanks.
hi roger-
I just finished my kerdi install on my tub shower. Kerdi fix was put at the tub lip under the drywall bottom and I think I am suppose to put caulk in the gap between the bottom tile and the tub how big should that gap be and what kind of caulk. second question is thatwhen I put my hand over the kerdi it feels like there is nothing back there I am concerned but it is stuck to the walls I pushed all the tiger strips out mortar came out also but as long as it is attached am I okay. Also I am using large tiles to hang on the wall above tub to the ceiling the onlyproblem is that I cannot find a large
tile unmodifies TS I am using 13 by 13 tiles what do you suggest I use ? I bought tec brand unmodified will this be ok? Also how do this big tiles stay up on such a thin membrane and how long before I can tile it has been about 8 hours since I did my last kerdi band? thanks so very much for your help!1
Hi Misty,
A 1/16″ – 1/8″ gap should be left between the tile and tub and filled with 100% silicone. I don’t understand what you mean when you say it feels like there’s nothing back there. If the kerdi does not have tiger-stripes and is a consistent color from embedding it into the thinset then it’s attached. Tec unmodified it fine for your tile. You can tile now – you can begin tiling as soon as you finish installing your kerdi.
Doesn’t matter how big individual tiles are – one square foot of a 6 foot x 6 foot tile weighs the same as a square foot of the same tile in 2 inch x 2 inch squares – one square foot is one square foot – whether they are one tile or 144 different tiles.
thanks roger for the info. I am concerned about the tiles slipping down Can I use a ledger board with the kerdi and seal up screw holes with kerdi fix? also should I start tiling up on the second row and do yhr first row last? which wall would you suggest I start with back front (with the fixtures) or the long side wall? thanks again roger and have a nice weekend.
Yes, you can use a ledger board and seal the holes with kerdi-fix. I normally don’t start with the second row – I start with the first. You can if you want to, though. Start with the longest back wall which is the first seen when looking into the shower. It normally leaves a better appearance if that is the one the other walls butt up to.
I have an older shower it is tiled about 4 feet above the tub, and it’s not high enough to take showers without getting the walls wet. Right now the walls are some kind of laminate or plastic coated backer board with tape as caulk?? What can I do with the walls and still leave the tiles alone?
You’ll need to remove all that plastic board and see what you have there. I have no idea what it may be.
I believe it will be sheetrock, what shoud I put over the sheetrock without removing any tiles and do I meet them up with caulk or what?
You can use kerdi over it and place a bead of silicone at the bottom where it meets the current tile. You can also use redgard it you want. It’s not recommended but there may be no waterproofing behind the tile that is currently there anyway.
Hi Roger,
We are using 12″x12″ sheets of 2 1/4″ mosaic tile for our shower floor. What is the best way to cut this tile? Some recommend tile nippers, while others recommend a wet saw. If I use the wet saw, should I leave the tile attached to the sheet or remove it and cut it individually? I wouldn’t think I could get a nice clean edge with tile nippers.
Hey Dan,
A wet saw cut’s ‘em just fine. I can use nippers and get a nearly perfect cut – after 21 years of practice.
Use a wet saw.
Should I leave the tiles attached to the sheet or separate them and cut them. I’m concerned that the tiles may move slightly while I’m cutting if they are attached to the sheet.
I cut them on the sheet. They normally don’t move. As long as you take your time with it you’ll be fine. You can take them off if it’ll be easier for you, just seems like more work than needed to me.
Thank you for the help!
Hi Roger,
Have you ever used PVC Beadboard for the walls of a walk-in shower instead of tile ? The wife really likes the look but we’re not sure if we will end up with more problems than it’s worth ? I’ve already created the enclosure with Durock and Redgard topical membrane. Not sure how I would attach the beadboard to the membrane ?
Hi Shawny,
PVC rather than tile??? Whattsa matter with your wife?
I’ve never done it nor seen it done. The only thing I can think of that would not fail as a bonding agent would be epoxy. I don’t know what kind of problems you may have with an installation like that.
I’m a lot of help, huh?
Hi Roger, so I live in Canada and it gets kind of cold here…it probably gets chilly in Colorado too. My question is regarding the mold sandwich, if I install the kerdi right moisture shouldn’t get through to my substrate and cause this moisture problem right? I guess my concern is cutting slits in the vapour barrier that keeps the insulation from getting wet.
Thx, Earl
Hi Earl,
Correctly installed kerdi will allow absolutely no moisture behind it – ever. You will, however, have moisture which seeps into the substrate as you are installing the kerdi, so moisture will get back there. If the plastic is left intact it will have absolutely no way to dissipate and will begin to grow mold. The insulation will not get wet if you install your kerdi properly. Kerdi will serve the same purpose once installed – it will simply be 1/2″ farther away from the insulation.
Hey Roger,
I just have some basic questions about tiling in general. I am finally getting to the stages of tiling in my bathroom remodel wooo hooo! I have been doing some research online, and I remember you saying that some of the things online are not the right way of doing things so I just have some questions to ask you.
We are tiling the wall about half way up in the main part of the bathroom with 6″ porcelin tile with a rectangle block glass tile border in which we are going to carry both over to the shower transition for the walls in the shower, I was watching some you tube videos
and they all show as part of the step in laying wall tile to use a baton they were calling it about 1/4 of the way up the wall so that the starting course of tile could sit on so it will not move, is that baton really necessary? I am asking because I just finished my 3rd coat of redguard in my pretty red shower now and I really do not want to screw anything into my shower membrane, it’s supposed to be a water barrier and if i penitrate the water barrier then it really would not be a barrier anymore. right?
My other question
,
Since I am carrying the same tile over to the shower walls, I really need to make sure my grout lines or courses line up across the wall so it does’nt look like crap. the floor is at a different level of the shower about 3″, is there any tips or tricks to calculating and planning my tiling so it does not look like an idiot did this?
Thanks in advance for all of your help, I am very happy i stumbled upon your website because my dog would have imploded and my four cats would have shit the bed by now. also my apologies for my spelling, at work right now and not alot of time to write this.
Hey Damian,
You are correct, you’d need to fill the holes with silicone or paint more redgard over them if you use a ledger board – I don’t use them. You do not need it.
I normally start with a full tile above the floor in the rest of the bathroom and draw a level line into the shower from that, cut the bottom row of tile in the shower to that level line. It will keep all your grout lines at the same level.
Get back to work!
Hey Roger, like the ebook, but still couple of quick questions.
1) I’m going to use Hydro Ban as my moisture barrier. Should I still use silicone in the corner of my cement board, or go ahead and tape/thinset that part too?
2) Using porcelain tiles mix of 6″ and 12″ with a 3″ glass listello, what size trowel? Plan on using Versa Bond. Bag shows diff sizes trowels for diff size tile, but not sure what to do when mixing sizes?
3) Liked your write-up on SprctraLock Pro Premium grout. For someone without a lot of tiling experience is it still a good way to go, or would I be better off with a non-epoxy grout? Seems like the previous tile jobs I did I had hard time with grout, mainly keeping color consistent. Do the actual installed colors look pretty close to the samples/whats shown on the box (like do you find them to look that, or do you find them to be lighter/darker)?
Hi Rudy,
Silicone the corners and tape and mud the in-plane seams. I normally use a 3/16 x 3/16 for everything, tile size doesn’t really matter too much.Epoxy is a bit more difficult to work with but the color is always an exact match to the samples – always.
Hey Roger
I am a handyman that has never installed tile. But am for the first time doing it (Nervous YES) and was wandering what is the best silicone to use for my corners. It is ceramic. Thanks fer all the info you dish out.
Ganeys
Hi Shannon,
You want 100% silicone. Most tile manufacturers make a silicone which matches the grout – that always looks best. But as long as it’s 100% silicone you’ll be fine.
Thanks fer the info Roger
Roger,
Thanks for your advice on managing the wall to tub transition when using kerdi-board. Interested to know if you have any experience using prefabricated shower recess like the quickshelf wall insert (i.e., http://www.quickshelf.net). Generally, would like to get your opinion on the pros/cons of using something like this. Also, would you recommend installing this with the flange over or behind the backerboard?
Thanks,
Matt
I have used the prefabricated niches a couple of times. They work fine for what they are, but I no longer use them.
They all work as described and are quick. The reason I don’t like them is that they are all standard sizes which never, ever match up to my tile. I prefer to build my own which I can create in any size to match my grout lines, inserts, tile size – whatever. If you use those you’re stuck with that size.
The waterproofing of all of them rely on the flange being installed over the backerboard rather than behind it.
When doing a leak test, should you expect some evaporation over a 24 hour period? I have a 48 x 41 pan and water went down about 1/8th of an inch in about 18 hours. What do you think?
Hey Andy,
It will evaporate some, but that sounds like a hell of a lot to me. Drain the pan and roll back the membrane to see if there are any wet areas either on the wall or in the deck mud of the pre-slope. It should not have gone down that much. Not saying it won’t, just saying that sounds like a bit much. Be sure to check around the drain as well.
I’m wondering about overlapping tiles in the corners of my shower. I realize there will be a gap, but does it matter if the surface of one tile extends along the edge of the perpendicular tile? Think of a box join with overlapping sides. I’m thinking that the caulk may adhere better to the edge of a tile vs. the face if it. I hope I’m making sense. Maybe I’m over thinking it, but just want to be sure I get a good seal in the corners.
Also, I was wondering about the appearance of Spectrlock. Does it look any different from typical sanded grout, i.e. would you know by looking at it that itis epoxy?
Thanks’ I really appreciate all the great info on your site!!!
Hi Jay,
Silicone will stick to anything, including the face of the tile in the corner. As long as you get that gap full and pressed in well as you’re tooling it you will get a very good seal.
If you look really close at the spectralock you can tell the difference, a casual observer (one not looking to see what kind of grout you have) will never notice it.
Hellooo!! I love your site and have goine through each step listed in preparing my bath/shower for tile. So here I am ready to tile. I am using subway tile and currently figuring out my layout. What size gap (for caulk) do you leave between the tiles on the inside corners? Thank you!!
Amber
Helloooooooooo! (Did you just type at me in the stomach voice from Seinfeld???
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1/16″ – 1/8″. I prefer 1/16″.
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