That pesky tub flange. You have the tile backerboard installed and everything is waterproofed. Everything except that gap between the backerboard and the tub flange. How do you waterproof that?
What to do with the tub flange?
Caulk the gap
Probably the simplest way is to caulk the gap with 100% silicone or a urethane sealant. First you would waterproof with your favorite liquid waterproofing membrane of choice. Ideally you would leave 1/8 inch gap which would then have sealant applied to it. Either stopping the cement board above the tub flange or alternately shimming it out and dropping it down near the tub would both be good options. Shimming it out is probably only feasible if the tub has a really skinny flange like a lot of the steel tubs do.
Band the flange
Seal and (mesh) tape the seam
This is what I’ve been doing lately. I usually have some Wedi glue in my van and have been placing 2 inch alkaline resistant mesh tape over the seam and gluing it with wedi glue. Utilize whatever you have- Wedi glue, Kerdi fix, or a waterproof polyurethane sealant from a hardware store. Using a small putty knife spread the sealant smooth across the mesh tape. The mesh tape makes me feel a little better about bridging that seam.
The reason that I don’t recommend the mesh tape with step one (silicone) is that the silicone will act as a bond breaker to thinset if it’s smeared over the surface. With Wedi glue (or something similar) you can adhere tile to the surface of it. So with method #1 you want to keep the sealant as clean as possible and in the gap only- not on the surface.
There you have it. Three different ways to treat the tub seam. None according to instructions. All preferable to doing nothing.
Jason Jay says
Hi,
I sent you an email and then saw the note that we should leave a message in the comment section.
The short story, (long in email). According to my plumber, I have flex in my shower floor. I’m using a Durock shower kit. Followed instructions, but plumber thinks the thinset was too thin and is crumbling. Called his tile guy and they suggested the following: buy can foam, drill down to thinset, inject foam, and hope it works. My concern, since all there is a styrofoam fleece and waterproof membrane over the thinset, won’t this balloon the floor? Should I put down some weight on the floor? Before or right after the foam? This is a last ditch before ripping the floor out and starting over. And if that happens, we’ve already tiled the walls, so is there anything I can do to save the wall tiles?
Thanks.
Jason
diy tile guy says
It’s hard to know if the foam will solve the problem, or not. You could try it and see if it takes the flexing out. I think weighting the pan immediately after injecting the foam would be a good idea. Also, you’ll want to make sure that you patch any holes that you put through the waterproofing which is the shower pan.
If you need to replace the pan you will need access to the joint around the perimeter where the wallboard meets the shower pan. If this is already tiled then this row of tile will need to be removed.
Paul says
Hello, great blog. Thank you for putting all this together.
If you caulk the gap then does the waterproofing membrane interfere with silicon adhering and do you have to get the membrane into the gap to cover the edge of the board so you don’t end up with a bare seem between the membrane and silicone?
Would the liquid membrane adhere to the tub flange? Can you cover the tub-to-backer gap with fabric strip and liquid membrane?
diy tile guy says
I find that it works best to apply the liquid waterproofing membrane first, let it dry, and then use the urethane across the gap. The urethane will stick to the waterproofing but the waterproofing won’t stick as well to the urethane.
You could just waterproof all the way down and use fabric like you mentioned. But I think it’s advisable to scratch the tub flange up with sandpaper, or something, to help adhesion. Also, the gap between the tub should be filled with something. Preferably something flexible which is why I like urethane and tape for this.
paul says
Ok, got it. Is the tape there for thinset to grab on to? When you put tiles over the flange, do you cover the seam and flange with thinset and adhere the tile onto it or do you just let the tiles hang over the flange leaving a void behind it? Would water get in there and sit on top of the silicone seal at the bottom?
What do you do where the backer joins the tub at the very edge of the flange and on the side? More caulking? I’m hung up on the edge cases, as you might see from my posts. Backer-to-backer and backer-to-drywall seams and corners are relatively straight forward and at least well covered but I don’t often see what to do where the surface meets plastic or enamel (i.e. window or tub). It would be awesome if you could do a blog post on this.
Thank you for your answers, both here and to my other posts.
diy tile guy says
If the flange is flush with the drywall then I thinset the whole space. If it’s set back in then it depends but usually I’ll keep that gap clean. It is theoretically possible for water to collect there behind the silicone gap. It’s nice if you have a tub with weep holes but not all tubs have them. Weep holes are indentations near the front of the tub designed to let water out before going over the edge. If your tub has them- don’t grout them in.
For the sides of the tub I caulk to the backer board. Here I will tape it off so it doesn’t make a big mess. You do have to be a little more neat and clean in this space as the tile won’t cover as much of the seam as it does at the flange.
I’ll look and see if I have a photo of caulking to a window or tub. If I do I’ll post it on my Twitter account (@Diytileguy).
paul says
If the tiles are hanging over a gap, will there be a problem applying the grout because there’s not a gap with a bottom to pack it into? Will it all just play-doh factory into the void behind the tiles? Can you place backer rod in front of the flange and thinset the tiles over it just so there’s a backing?
diy tile guy says
Yes. That would be an option.
paul says
One more question: Do you do anything to waterproof the screws holding the flange to the studs?
Thank you for your answers.
diy tile guy says
The technique above will put waterproofing over the screws. I don’t do anything besides that.
Braden says
This is so helpful. Thank you for all you do. Forums are a mess and this is a nice refreshing place to get info.
I did a version of your first suggestion and caulked the gap between the backerboard (Hardie) and the flange. Some of the caulk smeared between 1/2 inch 1 inch onto the bottom of the backer board. I tried to scrape most of it off but it soaked into the board pretty good. Then I applied RedGard down to the caulk line. Then I went over with silicone again on some of the places where the RedGard was peeling off the caulk. It is sealed and holding fine now. Is it reasonable to expect it will continue to do so or did I do something wrong? One end of the tub is already covered in tile, so I could rip it out and redo it if necessary, but I’m not excited about that.
diy tile guy says
It sounds to me like you’re probably ok and that you have the entire board covered. Thanks for the comments!
scott hamilton says
My customer has one of those big vinyl rimless (flangless) tubs. This means that when they fill the tub it will probably flex down. I will be using Kerdi on the walls. What is the best method of water proofing the gap between the Kerdi and the tub? Thanks.
diy tile guy says
I don’t have a link, at the moment, but if you look through my Twitter feed I posted about this just in the last two weeks.
Schluter has a new product designed for this exact thing.
Otherwise you can try to use Kerdi band and Kerdi fix and see if you can seal things up that way.
Peggy Kohus says
Help! Menards sold me a drop in whirlpool tub because I did not want an apron but it is to fit in a five foot alcove. So now tilers are saying there’s no way to fit the tile and flange on a drop in edge. Can you help?
Kristen says
Thanks for all of your posts and awesome information! It has proven to be most helpful with our DIY tile job!
diy tile guy says
Thanks!
paul says
Finally started ripping into the tub surround. I expected a thin flange so I was planning on furring out the studs and dropping the wallboard past the flange. If I was wrong and the flange was thick, I just do any of the methods above. Naturally, my bathroom is plan C so it’s a thin flange but the flange is on top of the old wedi board.
Looks like I’ll be using one of the above sealing methods because it’s about 1/2″ out but do you have any suggestions for filling the space behind the flange? It’s holding steady now but it’ll probably be loose once all the walls come out. I could add wooden shims but I can’t nail them down through the flange. Trying to squeeze cement board between the studs and tub flange to replicate the current arrangement seems like a bad idea.
diy tile guy says
I think sistering to the studs would be the way to fix it. If I understand correctly, the issue is that the flange is about 1/2″ away from the studs?
If so, you can screw a new stud directly into the stud that’s already there- only it would stick out about 1/2 inch further than the existing stud.
This is a good way to fix walls and if you do this start with each corner and once you get the corner studs plumb and straight you can put a straight edge across them and fill in the middle studs. The middle studs would sit right up to the straight edge and then your whole wall would be straight and ready to tile.
Hopefully, that makes sense. Let me know if I’ve misunderstood the question.
edit: also you could install plywood over the back maybe? that doesn’t straighten out studs though.
paul says
The issue that I’m worried about is that the tub is ~1/2″ from the studs all around because they installed it over the wedi panels. The panels came out and now there’s a thin strip of foam and wedi glue wedged between the flange and the studs. It seems pretty sturdy so I guess I could just leave it but that doesn’t seem right.
Info about getting the studs straight is good too, I’ll have to do that next. Thank you.
paul says
Ok, I re-read my new post and it doesn’t really clarify anything. I’m worried about the gap between the flange and the studs. Keeping the tub firmly in place is the issue and how to anchor the new supports, not joining the wallboard to the flange. Sorry.
diy tile guy says
I understand now and I agree that if the Wedi board is keeping things in place I would probably just leave it alone. You still may have to shim out the studs but maybe only slightly.
I’ve found drywall shims to work well for this. You may already be aware of these but others reading may not. They are in the drywall section of the hardware store and are cardboard strips. I staple them to the studs and flatten out the walls that way.
But yours is a good example of reading, planning, and preparing only to still run into the unexpected. That’s remodeling and that’s life. 🙂
paul says
Certainly can’t argue with the last comment and thank you for all your help.
The framing is actually kind of a mess. There’s a bunch of random blocking that needs to be re-done and the studs themselves are kind of a mess. My tentative plan is to sister the studs out by 1/2″ on the side walls. This will take the wall board past the tub flange. The sisters will be cut in at the bottom so I can attach the tub flange to them. The back wall is up against the flange so that will get shimmed and spaced out with plywood. Does that sound reasonable?
Also, if you space out with plywood, do you need to use longer screws for the wallboard?
diy tile guy says
I think it sounds reasonable. With using plywood for the back I don’t think you would need longer screws. If anything, shorter might be preferable because I think you can just screw into the plywood. 1 1/4 inch screws are the shortest that I’ve seen for cement board screws though.
I don’t think them passing through the plywood is an issue unless there’s something behind that you don’t want them to hit. Taking photos and mapping out anything important is a good idea.
paul says
Oh, you mean putting up whole sheets of plywood like sheathing a house exterior? I meant just put strips of plywood over the studs to space them out. I just looked at that wall and the studs are pretty uneven. I may actually have to put shims under the plywood strips (or sheets).
diy tile guy says
You could just put up 1/2 inch strips and that would save on the plywood. But, in that case, I think you would want longer screws to get into the stud as opposed to just the ply.
And I definitely recommend the drywall shims. The flatter you get the wall now the easier it will go later.
paul says
Not so much a question as just sharing relevant experience. Just finished cleaning up the rim and flange on my americast enamel steel tub. The foam board was behind the flange and tile was set over it. They originally grouted the tub/tile joint but I had ground it out and put in silicone instead. So it was coated with a combination of silicone caulk, wedi glue, grout, and thinset. (I think it’s wedi glue, it’s blue and I think the foam board was wedi board.)
The mortar/grout tag-team had to be removed with a combination of razor blade, wooden scraper, and scotch-brite pad. Couldn’t quite tell which was the grout and which the mortar but I think the mortar formed thick caked on lumps that had to be broken up with a hammer and punch in places.
The wedi glue pretty much came off by rubbing it with your finger. The silicone on the other hand was a real champ: it had to be softened with paint thinner then scraped then the residue rubbed off with the scotch-brite pad.
I don’t know for sure if that means the silicone is going to form a better seal than the wedi glue but it’s definitely more tenacious. I’ll definitely use silicone sealant rather than the Wedi based on this experience.
diy tile guy says
Good feedback and that’s why silicone is so much better than the easier-to-install acrylic caulks that many people prefer.
But it’s not all about adhesion either. How much a product stretches and how big of a space it can fill is something that comes into play also. Additionally, Wedi glue is a light gray color. Not sure what the blue color would be.
But thanks for sharing your testing and I’m always interested in real-world results.
paul says
It’s a light gray with a blue tinge. I keep thinking it’s blue because there was blue foam stuck in it.
Dino Morelli says
Hi Tile Guy,
Looking for some advice for my tile install. I am conflicted about which Ditra product to use. I am planning on installing a 12×24 9mm ceramic tile but would like to end up flush with the 3/4″ hardwood. The Schluter website says to use XL for perfect transitions to hardwood, but that is with 7mm tile. With either approach, what would you recommend as far as trowel sizes? Ditra thickness?
diy tile guy says
You’re kind of in that in between area but the 1/4 inch Ditra XL if probably still the better choice.
However, if you have a hump in the floor, especially in front of the door, then you would probably be better to flatten the floor and use standard 1/8 inch Ditra.
For trowel size, a 1/4 x 1/2 inch or 1/2 x 1/2 would be the sizes that I would use.
Ira says
Hi there,
I am doing remodel of my bathroom. The questions is which tile end giving more kodern look, the bullnose or the schluter? Thank you!
Ira says
* modern
diy tile guy says
Metal profiles are more of a modern, minimal look.
DM says
Great, thanks for your insight, much appreciated!
Richard Hadley says
Tile guy nice site for information on tile issues. Great job. Rick from Chicago area. Redoing small full bathroom completely down to studs and subflooring. What are your thoughts on Ditra heat underlayment?
On Kirdi board or WEDI board which do you prefer?
Have you ever installed a Kohler castiron showerpan Selient? Concerns about the flanges on alcoves if you look up details on flange you’ll see what I mean. What do you think about marble honed tumbled in shower? I see alot of people say they would never do natural stone ever again in shower area. The regular sealing maintenance is a concern for me But love the real look of Queen Beige honed marble. Thank you. Rick.
diy tile guy says
I like Ditra Heat underlayment and have a post on it with a couple of tips. https://www.diytileguy.com/ditra-heat-mat-installation-ignore-rules/
My personal preference between the two is for Wedi board but have no issues with Kerdi Board. Either is fine.
I’ve tiled over a Kohler pan before but it was quite a while ago. The Kohler instructions show that they want the walls furred out so backer board drop down past the flange. If that works for you then that’s the way to do it. If you have tile that aren’t very small then I don’t see why it wouldn’t work to put the backer board above the flange.
I do not recommend natural stone in a shower- especially over the more modern “bonded” waterproofing membranes. I’ve seen too many darkening and staining issues. Porcelain tile doesn’t have the same issues and is much easier to maintain. However, some people are set on natural stone and there’s no talking them out of it.
paul says
Have you had to set and level a tub? I’ve got an american standard americast tub (enameled metal with foam backing, looks like). The instructions say to set it on a rectangular area of silicone bead but I can’t find regular silicone in larger tubes and it would take 4-5 10 oz tubes to get enough. Instructions also say a mortar bed is acceptable so I was going to put down 1/4″ of flexbond and set it in that. It doesn’t seem to need much leveling, I test fit it and there was only 1/8″ height difference front-to-back and 1/8″ end-to-end so this is mostly to keep it steady. Any advice?
diy tile guy says
I hire plumbers for installing tubs so I don’t have any hands-on experience but I’ve never seen one set with silicone. I can’t even figure how that would work.
Mortar is generally used to level them out. thinset isn’t really the right thing and I think you’ll need more than 1/4 inch. But you don’t need tons of it and a stiffer consistency is what you want. You want to set the tub, level it, secure it, and leave it alone until the mortar cures.
That’s about all I know. 1/8 inch is a pretty good starting point. Most tubs need more leveling than that so I think you’re in good shape with just a little bit of adjustment.
paul says
I think the silicone in the instructions is just there to keep it steady, dampen any movement, and fill gaps. It’s just a 1/4″ bead under the ~1.5’x4′ waffle-pattern “foot” of the tub that sits flat on the floor. I figured the thinset would serve a similar function. When I took it out, it was sitting on top of the edge of the old mud bed floor, a stringer on the back wall and a composite decking plank down the center. I replaced some of the bad subfloor planks and put down 1/2″ plywood below it.
How level is it expected to be? I thought 1/8″ out of level might be good enough. I was hoping to avoid having to shim up the apron but if thats’ what I have to do…
diy tile guy says
1/8 inch is workable but the better that you can get it the easier it will go.
paul says
I worry that I come across as argumentative. If I do it’s not intentional. I always appreciate your answers. I, and a lot of other people, would be up the crick without your help. Thank you.
diy tile guy says
It doesn’t come across that way at all. You are one of the more active members of this community and your questions help others. I appreciate your contributions and willingness to participate.
Brad Bromich says
I have a Sioux Chief tile shower drain. We had a clog and instead of the water backing up into the shower, It backed up as high as the flange and went over the flange and under the pan liner and leaked out onto the subfloor and through to the basement. Is that supposed to happen?
diy tile guy says
No, that’s not supposed to happen.
If the shower contained the water then the water should evacuate down the drain. If it gets under the liner then it could be that the bottom of the shower liner isn’t sealed to the drain flange.
If this happens when water backs up then this is probably the cause. The underside of the shower liner is supposed to be sealed to the top of the drain flange.
paul says
I’ve got a gap under the front apron of the tub. It’s higher in the middle and sits on the ends. Not sure if it’s bent somehow or if it’s normal for american standard americast tubs. I was going to put shims under it to get it overly level and support the front. They’re pretty thin at the ends but close to a quarter inch thick in the middle. I’ll do the Ditra/Kerdi-Band/Kerdi-Fix waterproofing at the base of the tub. Is the Kerdi-fix strong enough to fill and hold up the gap under the apron or is it too soft? The bottom of the tub will be sitting on mortar.
DIYTileGuy says
As long as the tub is supported by mortar I don’t think a gap is an issue. The apron is simply cosmetic and you don’t want that supporting the tub. That’s my understanding anyway.
I don’t think Kerdifix will support the gap but it will fill it in and seal it. If you want something to fill and support I think a spray foam product might work better for that.
If you are tiling the floor then the tile should hide the gap at the bottom of the tub.
paul says
Time to get the studs straight in the walls around the tub. I want to get advice so I don’t start on something over-elaborate and pointless. I’ve been asking about this here on and off for months but I want to get a good plan now that this is the next step in the renovation. The situation is the house is 70 years old, the bathroom started out with mud walls on metal lath, and the studs are all out of whack. It was plaster on purple board and foam board by the time I got to it but the tiles were smaller and not all that straight. The studs are as much as 1/2″ out of plane, crooked, curved, twisted, and I need to shim them out about 1/2″ to come out past the tub flange.
I already did the wall at the faucet end of the tub by sistering most of the studs. A few were shimmed with thin planks I ripped to proper thickness on a table saw. This wasn’t too bad and I’d do a better job if I had to do it again but it took a lot of planing and some of the studs will need shimming with cardboard shims. I think I’d like to go another way for the other two walls. The short wall along the long edge of the tub is exterior and the space is better used for insulation (which is already in place). There’s also a window in it so the structure is complicated.
There’s a few ways I’m considering. Covering the whole thing in plywood then attaching the CBU to that as you suggested sounds pretty good but I would want to shim out the studs to keep it flat. Can I put up shims at regular intervals like 12″ then attach the plywood at these points? Can I do the same for narrow strips just along the studs? My next best idea was to trace the contour of the stud bow on a straight-edged 2x, cut it out, and screw it to the stud. Would it be a bad idea to put furring horizontally across the studs and attach cement board and drywall to those? I could just uniformly shim out the studs with plywood, attach CBU over the crooked shimmed-out studs, and rely on planitop but that doesn’t seem structurally sound; a lot of bend in the CBU and a lot of patch.
You’re not just about to put up a post on flattening out walls, are you? I would appreciate any tips. I can take pics if you want illustrations, hopefully not under “what not to do.”
DIYTileGuy says
Hi Paul, of all the things that you mentioned the only one I really like is the horizontal cross-blocking option but the cross blocks would have to be 16 inches on center at a maximum.
But if you can get the bottom flat across then do the same across the top this would allow you to simply put a straight edge on both of these points and bring the center cross blocks out to the straight edge. This would keep everything flat and inline with each other.
Otherwise, sistering is a good way of doing it but I understand that you would rather have insulation in there. Also, planing and shimming can work but it sounds like your existing framing is pretty uneven.
I don’t have plans for a wall flattening post in the near future. I did do some filming for one before my GoBoard post but it has some gaps and missing segments so it will have to be revisited down the road.
paul says
When I mentioned that horizontal option, I meant lay 1×3’s or something similar perpendicularly across the faces of the studs similar to what they do for ceilings around here, not add horizontal blocking between studs and attaching to those. The cross-blocking is an option as well but seems like if I’ve got room to do that I may as well sister and plane. Flat furring across stud faces doesn’t give me a lot over just putting it up vertical along the stud as a shim other than that it’s flatter because it doesn’t pick up the twist of a warped stud. It’s also a bit easier to add shimming behind it if there’s insulation in the wall.
How much is it safe to bend a sheet of permabase CBU to put it up over warped studs? If I ever find a place that sells planitop around here, I may just have to rely on that to flatten things out.
Too bad about the post. Can’t complain with all the helpful information you already have here. Thank you!
paul says
If you have cement board mounted horizontally above the tub and overlapping the tub flange, do you try to avoid having a tapered edge at the bottom? Sounds like a choice between a flat edge or an edge that’s less likely to crumble.
DIYTileGuy says
I much prefer the tapered edge. Not really sure why but crumbling would certainly be a factor.
paul says
Could you please recommend specific brands and types of sealants that you use? There’s kerdi-fix and wedi glue but are there any particular silicone or urethane sealants that you use?
DIYTileGuy says
Typically, I use Wedi sealant as I always have it on hand. I usually use color matching silicone that matches the grout.
Sometimes I will buy generic white 100% silicone rather than the “color matching” version. Usually, this is either DAP brand, Premier Xtrabond, or the newer Gorilla brand. I usually stay away from GE 100% silicone but that’s based more on 2nd hand rumor than my actual experience.
Bostik Ultraset is one of the best urethane’s around (my opinion) and it’s really expensive. But it’s one of those “if you can’t do it with “X” then it can’t be done” products.
Lastly, if you are looking for alternatives to Wedi or Kerdi sealant you could always consult the GoBoard Alternative Sealants list. Sika has a good reputation and I know one industry person that speaks very highly of OSI Quad Max- both listed on the GoBoard list.
https://www.jm.com/content/dam/jm/global/en/tile-backer-boards/GoBoard%20Sealants%20Caulk%20Notice-%20Jan%202018.pdf
paul says
Thank you, that is very helpful. The substitute sealant sheet is great. Do you have an opinion on MS polymer vs straight polyurethane?
I looked up Bostik ultraset and it looks like it’s a waterproofing membrane that comes in a bucket. Did you mean Bostik 915 or did they change it?
I started on this because I was looking at sika and noticed that they don’t recommend it for vinyl surfaces so I can’t use it to seal redgarded CBU to the vinyl window. Would be nice to use the same stuff to seal the gap between CBU and both tub and window frame (not to mention substitute for Kerdi-fix to seal ditra to the tub).
DIYTileGuy says
I don’t have anything intelligent to add to MS polymer vs polyurethane. I don’t know enough about the chemistry.
Ultra set comes in a sausage tube and it’s fantastic tenacious stuff. But probably not what you are looking for.
Didn’t know that about Sika. I don’t use their products all that often as I usually have something else on hand but it’s good to remember.
paul says
In case you’re interested: I emailed Schluter tech support and asked if kerdi-fix can be used to seal surround to a vinyl window. They said that a) it adheres to vinyl (good to know) and b) can be used in wet areas (I sure hope so) but c) I should contact a regional representative to get help with my specific application.
DIYTileGuy says
I’m glad to hear this because I’ve used it for that very purpose before. 🙂
Maria says
I would like to know what needs to take place to tile on a concrete wall. My contractor says Redguard should be sufficient but there is a large gap on the side of the tub between the concrete wall and the tub. What should he fill it with and how do you make that area waterproof before tiling? Also, he placed hardiebacker over the two sides that had drywall I read that it should be attached directly to the studs instead and that drywall should be removed.. My biggest concern is the waterproofing because I’m on the 10th floor of a building. Thank you in advance.