View Full Version : Question about drop in tub installation in a 3 wall alcove.

04-07-2011, 10:03 AM
I have a Kohler drop in bathtub. (K-1510) It will be used in a 3 wall alcove, so I also have the tile bead (K-1177) that is used around the edge of the 3 sides of the tub that will be up against the walls. The installation directions do not have anything about using a 2x4 ledger on the 3 walls. In fact it says not to rest the rim on anything. Basically just to make sure it is level and set it in place in mortar. Since I am not using an integral apron, I will be building a wall to tile on the facing side. The instructions on this also say for it not to touch the rim of the tub, but to leave a small space to be caulked between the tile & the tub. So really the only thing holding it in place is mostly the mortar, since the tile bead would not be used to "nail" or secure it into the stubs. Is this enough to keep it from lifting up or moving side to side? I just want to make sure I am doing this correctly as it is my first time. I'm just a DIY'er, so any help on installation would be much appreciated. Thank you very much.



04-07-2011, 11:09 AM
You could put a ledger under the rim, but don't let it actually hang from it. This way, it couldn't rock if you say sat on the edge. With its inherent weight, it takes a fair amount to move it in the first place. Just make sure it is perfectly level sitting in the mortar bed.

04-07-2011, 11:50 AM
You will want to install a backer board on the back wall.
If the tub slides or sets in on a smooth level floor, then no shimming or mortar will be needed.
However, it the floor is out of level, then you will want to find the high point, and then using a level mark a line on the studs from that point; that point being the bottom of the tub deck measured from the high point on the floor. Then you will need to shim or mortar set the tub.
I find it easiest to install a level board on the back wall and build the front wall evenly, maybe making them a bit too high, and then place a few piles of mortar, placed so that they can squish down to the proper level. You don't want mortar to touch everywhere on the tub, just a few spots.

Too many times instructions call for a flat and level bed of mortar, but that is impossible to set up perfectly.
It's better to use the a bit of mortar as a fill in, and use the framing and support to ensure a level and true installation.

Anytime the bookworms that write those things want an education on setting a tub in a real house, just give me a call and we will go out and do one together.

04-07-2011, 02:56 PM
jadnashua, That makes sense. Basically having the ledger in place, just under the rim, but not touching. I guess it's just that fact that there is nothing physically securing it to the studs that seems so odd.

The installation instructions basically call for spreading 2 inches of mortar on top of the subfloor everywhere except for where the "leveling blocks" are, and setting the tub in the mortar and ensure that it is level.

I think I may be doing this old school, but for the surround I will be using layers of roofing paper behind cement board. the roofing paper would be sealed to the tiling bead to create one surface with the cement board on top of that (1/4" away from top of rim) Then sealing the joints between the cement board piece with 100% silicone before I tape and mortar the seams. I plan on just tiling on top of that. Is it worth also sealing the cement board with something like "redgard"? Or would the waterproof roofing paper & redgard create a moisture trap between the two? Just wondering.

04-07-2011, 04:42 PM
You could use plastic sheeting or the roofing felt behind the cbu or use a waterproof membrane on top of it, but not both. CBU generally specifies the use of thinset and alkalai resistant mesh tape on the seams, not silicon; the vapor barrier behind it is sufficient. If you want to use RedGard on top, you need to tape and thinset the seams first, let them cure at least overnight, then coat the the RedGard. Use some caulk to fill the seam between the tub and the cbu.

04-07-2011, 06:37 PM
If you plan on using a ledger board that doesn't touch, well............that's the same as no board there at all. Good job.
Save a step and just leave it out. And then when someone puts weight on that part of the tub and it sinks, wonder why you didn't set the ledger board there so that it was in support of the tub deck.
You have found a new way to install these things. What contractors have been doing for decades was rather silly.

And tell me how the "smooth" mortar works out. That will be good for a laugh too.

You will find that mortar sets up very fast.

04-08-2011, 10:34 AM
Terry, now you see why a noob like myself is so confused. Everything I read is what you describe. And it makes all the most logical sense. So when I read the installation instructions that contradicts the logical, it just adds that confusion and trepidation. Thus why I am defering to your professional expertise. I think I am realizing there is a difference between "resting" and " hanging" or "supporting" . The latter would be bad while resting on the ledger with all 4 support blocks level on the floor would be best. And instead of a giant pile of mortar, smaller areas. Right?

04-08-2011, 10:42 AM
If you use mortar, then small piles that can squish out.

I have tried installing mortar level to the bottom of the tub. It's not like I didn't try it that way. I'm just giving you guys the benefit of my wasted mortar and time. Small piles that can squish out are the best.
If the tub fits flat without, then that may be even better. But for those times when things aren't perfect, then the mortar helps.