# Tiling over a bathtub lip



## The Kid

I am tiling a greenboard wall above a bathtub. I understand that the greenboard must be above the lip of the bathtub (not overlapping or underlapping), however, using this method will create a 1" gap (the length of the lip) between the top of the tub (minus the lip) and the beginning of the drywall. When applying tile, is it alright to overhang this tile over the gap? I see no other way to complete this project. I have tiled bathtub walls before but never paid attention to the gap or the lip because I was never the one to actually install the drywall before. This time, I'm doing both the drywall and the tile on top of it.


----------



## Big Dave

You need to take some hot mud and fill in the gap then after it is dry you need to skim coat and tape to keep it from cracking. After that install tile as normal.

Dave.


----------



## boman47k

I know this is a somewhat old post, but why not cover the lip with the wall board if you are going to mud it anyway? May have the same situation come up in the near future.


----------



## Get r done

boman47k said:


> I know this is a somewhat old post, but why not cover the lip with the wall board if you are going to mud it anyway? May have the same situation come up in the near future.


This is indeed an old query but I'm doing just this project now and have every intention of putting the hardy back directly over the lip. Why mud? that just seems like a waste of time and an invitation to cracking.:thumbsup:


----------



## afterhours

*backer board over the tub lip*

I've just done the same thing. Put my backer board over the lip of the tub. But, note that the backer board now warps a bit, so that the bottom row of tile will need to be cut at the corners (think gentle trapazoids) to fit properly. Ick.

Maybe should have done this with the mud trick instead -- then again, the whole bath is out of square (built 30 years ago by original owner)... so might not be much worse than if I had simply tried to do it right.

How did yours come out in the end?


----------



## Termite

The OP's decision to tile over greenboard in a tub surround is a big mistake, and is against code as well. This calls for backerboard!!!!!


----------



## buletbob

We have always installed our substitute on top of the tub rim. Caulk it and then pack it and tape it with thin set. this way you will not have that bump out around the bottom of the tub. other wise you will have to fur all three walls out to flush up the rim. BOB


----------



## afterhours

buletbob said:


> We have always installed our substitute on top of the tub rim. Caulk it and then pack it and tape it with thin set. this way you will not have that bump out around the bottom of the tub. other wise you will have to fur all three walls out to flush up the rim. BOB


I like this idea. I only have two of the three walls to worry about. Third wall (wet wall at that) had the tub lip inset into the studs. Had considered furring strips to bring the vertical plane flush with the 1/8 lip at the top of the tub, obviously didn't. I have the backer board screwed on now -- so it wouldn't be that big of a deal to remove it and trim off the bottom that fits over the existing tub.

Let me back up: am remodeling a 30 yr old master bath. Original home owner installed tub with additional pitch (can't fathom why, as the tub has its own pitch to drain), so there is a 5/8 drop from back of tub to front. All three walls are also barely out of plumb and not quite perfectly square. So any 'added' mistakes I make will only compound the issue.

I've got the backerboard all the way to within 1/8 of the tub horizontal surface, overlapping the lip. And laying out dry tile against it in the corner, boy there is going to be some odd tile cuts. So I think I read that you run your backer just down to the top edge of this lip on the tub, not overlaid (hence the furring comment). I don't want to assume anything here, but would trimming the backerboard back to the top of the lip, then packing the rest with tape and mud create any water seepage issues into the future?


----------



## buletbob

Yes cut the backer to the top of the tub flange.what I do is install a few roofing screws on top of the flange sticking out for the backer to rest on while I screw it off.
Next you will cover all the seams including the lip of the tub with fiberglass tape and thinset.
the only time you might have a problem is if the first row of tile on the tub is cut around that area. Dumb but have seen it. you should not have a problem with what I have suggested. you normally start with a full to a half a tile . I always start with the coarse above the lip when I start. Just tack a straight edge up and start from there. when dry remove and start marking and cutting your tiles for the top of the tub. What I also do is tape and thinset my seam at this point and then thinset the tiles over. the tile will help hold back the slack from the thinset and tape.
This process works well for me but I am sure there are other contractors how have there special technique also. Good luck BOB


----------



## slapdash

This may be a dumb question -- but is thinset really waterproof? If it is, why do products such as REDGARD and DITRA exist? 

I'm just about to tile my tub surround, and am very concerned about sealing the gap between the bottom edge of the Hardiebacker, and the lip of the tub. This has caused problems in the past, when water leaked through that gap and destroyed the kitchen ceiling below. Thanks.


----------



## buletbob

slapdash said:


> This may be a dumb question -- but is thinset really waterproof? If it is, why do products such as REDGARD and DITRA exist?
> 
> I'm just about to tile my tub surround, and am very concerned about sealing the gap between the bottom edge of the Hardiebacker, and the lip of the tub. This has caused problems in the past, when water leaked through that gap and destroyed the kitchen ceiling below. Thanks.


 I don't think that gap above the lip was ever filled with thinset. when you do it this time make sure you reinforce it with mesh tape that is approved for cement board. then you could coat everything with Redguard,


----------



## slapdash

buletbob said:


> I don't think that gap above the lip was ever filled with thinset. when you do it this time make sure you reinforce it with mesh tape that is approved for cement board. then you could coat everything with Redguard,


Yes, you're right -- the old setup was a thick mud wall (from 1930s). I tried to fill the gap between bottom edge of tile and tub with plastic backer rod and caulk -- but after awhile, it would fail and water would leak through.

My plan this time is exactly as you said -- fill up the gap with thinset and tape, followed by Redgard (since the installer forgot to put plastic sheet behind the Hardiebacker). He claims that thinset is waterproof. But my understanding is that thinset is like any mortar -- it can crack. Therefore, a membrane such as Redgard (or plastic sheet behind the cement board) is needed too. Please correct me if I'm mistaken. Thanks.


----------



## buletbob

is there a vapor barrier on the insulation in the bathroom? if so I would not use the plastic, you will have moisture building up between the to barriers which will bring more problems. BOB


----------



## cooper4x4

I have a question to expand on this same subject. When applying redguard, does roofing felt or some other vapor barrier need to also be installed before the cement board goes in? All of the walls on my bathroom are inside walls. 

Also, just to clarify filling in the gap around the flange. I would need to apply thin set to fill the gap and then tape over that with fiberglass mesh tape?


----------



## buletbob

cooper4x4 said:


> I have a question to expand on this same subject. When applying redguard, does roofing felt or some other vapor barrier need to also be installed before the cement board goes in? All of the walls on my bathroom are inside walls.
> 
> Also, just to clarify filling in the gap around the flange. I would need to apply thin set to fill the gap and then tape over that with fiberglass mesh tape?


as far as felt, plastic, I have never installed anything behind my backer unless it was a shower seat. and yes the fiberglass mesh tape is a must. GOOD LUCK. BOB


----------



## Termite

buletbob said:


> as far as felt, plastic, I have never installed anything behind my backer unless it was a shower seat. and yes the fiberglass mesh tape is a must. GOOD LUCK. BOB


Agreed. The redguard becomes your moisture barrier, negating the need for one between the studs and the backerboard.


----------



## okolonabill

Big Dave said:


> You need to take some hot mud and fill in the gap then after it is dry you need to skim coat and tape to keep it from cracking. After that install tile as normal.
> 
> Dave.


 
The best thing to do with this situation is to lap the backer board over the lip of the tub. This is necessary to help with water proofing, but first sand along the edge of the back side of the backer board to fit over the lip.


----------



## DerWookie

When we did our bathroom remodel we brought the cement board down over the tub lip. We used 1/8" furring strips on the studs to account for the lip and allow the cement board to lay flat, thus not having to make "trapezoid" cuts for the bottom row of tiles.


----------



## moblomeley

*Too late!*

I have a question that goes off of the topic above. Our contractor (don't ask) stopped the tile directly above the lip of our tub. Now what do we do? We are getting ready to put the house on the market and we can't sale with the tub looking like it does. We initially complained but got nowhere so we have been living with it for years. Can we add a trim tile at the bottom? Won't we have to build up the back b/c there is a gap (size of the tile) between the wall and the place where the trim tile would go. 

Help! Molly


----------



## Blondesense

Molly, It would be best if you start your own thread. Many regulars may see this is an old thread and not even bother reading it.
Don't forget to add pics.


----------

