Backer board around Kohler tub

[Angler2184]

I am remodeling one of our bathrooms. I am currently installing hardie board around the tub and am wondering if the board should come down over the tub flange or be flush with the edge. I attached a few pictures. If i do bring it down over the flange should i remove the screws and put in nails? Thanks

 

[Angler2184]

I just read on the kohler instructions that i should of put 1/4 furring strips to bring the wall flush with the flange....

 

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[Atomic1]

I have seen a lot of leaks at tub flanges from configurations like the one in your photos, and as a result, always prefer to see the outer face of the backer to be proud of the flange. This provides more resistance to water penetrating that joint.

 

[Angler2184]

I have seen a lot of leaks at tub flanges from configurations like the one in your photos, and as a result, always prefer to see the outer face of the backer to be proud of the flange. This provides more resistance to water penetrating that joint.

So, should i put 1/4 in furring strips on the studs and drop it down over the flange?

 

[Jadnashua]

You need a moisture barrier behind the cbu unless you're planning on using a surface waterproofing scheme. CBU is not damaged by being wet, but it is not waterproof.

If using a moisture barrier behind the cbu, it should come in and over the tiling flange of the tub. As long as your tile is supported a minimum of 50% on the cbu, it can overhang the lip. You want to use a good quality silicon caulk between the bottom of the tile and the tub - the tile should not touch to allow for slight variations in expansion/contraction between the two materials. If you would rather not use caulk, there are some engineered profiles that can be used between the tile and the tub (and, in the vertical corners, which also should not be grouted, but caulked or an engineered joint). A few companies make these, one that has a huge selection is www.schluter.com.

If you would prefer to make the entire tiled area waterproof, I might suggest using something like either Kerdi, or Laticrete's HydroBan sheet membrane. SOrt of like putting up wallpaper, but the stuff is waterproof and tileable. You'd seal that membrane to the tub flange with their banding material and a sealant. Schluter has a bunch of videos that show how this is done.

A good place for help with tiling is www.johnbridge.com

 

[Angler2184]

I got the studs shimmed out so the cbu comes down over the face of the flange. I will be using redgard to waterproof. When I checked the installed cbu horizantially with a 4ft level it seems good but vertically there is a couple spots where I have maybe 1/8 to 3/16. I will be tiling with subway tiles mosaic. Just wondering if this will be an issue...thanks

 

[Angler2184]

Seems like the bottom of the cbu is kicked out a bit

 

[Cacher_Chick]

When I am putting up wallboard, I use a 4' and 6' level to locate and shim out any of the gaps created by uneven or crooked studs in the wall before I put the board up. They make 1-1/2 cardboard strips that are 1/16" thick just for this purpose. I use a stapler to install the strips, and sometimes will have several overlapping layers of these shims to bring the wall out to a flat surface.

 

[Angler2184]

K thanks...it was the tub flange that was kicking the bottom out . I shimmed the bottom so it goes over the flange. Working on th next piece now. If the wall is off less than 1/4 in some spots is that ok?

 

[Cacher_Chick]

The more flat the backerboard is, the less trouble there will be in keeping the tile flat and without lippage. The waterproofing does not care if it is perfectly flat, but the more flat that the finished product is, the better it will look.

 

[Jadnashua]

A basic thinset is designed for a finished thickness of in the order of 3/16" max. There are some that can be installed thicker. If the backs of the tile are flat and the surface is too, you barely need any thinset thickness as the bond. It is MUCH harder to set tile when the substrate is not flat and achieve a flat finished surface.

Industry standards for a floor with smaller tile is 1/4" max in 10', and 1/8" in two feet. FOr larger tile, it's 1/8" in 10', and 1/16" in two feet. If the wall is not flat, it's quite hard to get the tile all in a flat plane, and, depending on the thinset you use, you may exceed it's design depth. Thinset applied thicker than design tends to shrink and crack, not something you want behind tile in a wet location.

If you haven't taped, thinsetted the seams, and applied the waterproofing...it might be better to just remove the sheets, straighten up the wall, then put it back.

 

[Atomic1]

One other thing i'll mention is the screw drilled through the mid height of the flange. How are you going to make that a long-term watertight? Even if a stainless screw was used, i see this as a problem. Usually, i see a screw installed so that the head catches the top lip of the flange, not through the flange.

 

[Angler2184]

I have the seams taped and filled...I have a question about tiling the walls from the toilet to the vanity. Do I need to use cbu or can I use 1/2 drywall?

 

[Cacher_Chick]

I have the seams taped and filled...I have a question about tiling the walls from the toilet to the vanity. Do I need to use cbu or can I use 1/2 drywall?

The CBU is more solid and resistant to change due to the drastic swings in humidity that take place in a bathroom. You can do drywall, but the only benefit to doing so is that it is a bit easier to install.

 

[Jadnashua]

Drywall will be fine outside of the wet area of the shower. Your choice. You don't want to use drywall mud on the seams, but should use the same tape you used in the shower and then, you can just add thinset when you tile it...no need to do the thinset first, let it cure, then continue. It MIGHT be easier if you do, depending on the size of the tile, and where the beveled edge ends up on the drywall. Use a long straightedge to screed the thinset flat if you do it first and then let the thinset cure so you'll have a flat surface. No need to do anything to the screws in a dry area, only the seams when tiling.

Note that the 1/2" Hardie board isn't really 1/2" thick like drywall (it's thinner) so if you're continuing the tile out of the shower onto the walls, take that into consideration.

 

[Angler2184]

I just realized that the drywall sticks out 1/16 higher than the cbu. Could I build the cbu up a touch with thinset ? Or should I move the stud I sistered back a touch. I added this stud bc I had to bring wall out bc of tub flange. If I move it back I should be ok but will have a bigger gap between cbu and drywall....close to 1/2 inch

 

[Cacher_Chick]

I just realized that the drywall sticks out 1/16 higher than the cbu. Could I build the cbu up a touch with thinset ? Or should I move the stud I sistered back a touch. I added this stud bc I had to bring wall out bc of tub flange. If I move it back I should be ok but will have a bigger gap between cbu and drywall....close to 1/2 inch

They make strips of material used to shim out the studs to make them all even before wallboard is installed. Shim out the last stud onder the CBU to match the profile of the drywall. Check everything with a long straightedge and float out the low spots if they are enough to be of concern.

 

[Angler2184]

They make strips of material used to shim out the studs to make them all even before wallboard is installed. Shim out the last stud onder the CBU to match the profile of the drywall. Check everything with a long straightedge and float out the low spots if they are enough to be of concern.

I've already thinsetted the cbu

 

[Cacher_Chick]

Looking at your photos it would appear that you can dig out a few screws from the edge of the CBU so you can sneak a strip of shim in behind it. There is no reason to move the whole piece to gain a 1/16" at the edge. If you already filled and taped the transition, then you may as well continue to float it out so it's all flat.

 

[Jadnashua]

You usually have enough thinset underneath the tile on the cbu so that you can still keep things level when overlapping onto the drywall.

Some cbu are actually 1/2" thick. HardieBacker is thinner.