Drop in tub Lip flexes with weight

[Cavan Merski]

Hi everyone I’m new here but haven’t been able to find an answer to my question anywhere. I’ve set a Koehler underscore drop in tub onto a mortar bed twice already and both times after removing the shims from between the tub lip and the decking the lip of the tub flexes as I move around in the tub. It flexes about 1/8” which seems like too much as the gap between the tub and the tile will flex and break.

One way to fix this could be to simply leave the shims between the lip and the frame and tile up to it. If I leave the shims in the tub lip doesn’t flex. Obviously this is putting some pressure on the tub lip as someone moves around in the tub but it seems minimal.

Has anyone fixed a problem like this before?

thanks!

 

[Cavan Merski]

Here is a picture of the gap I am describing

 

[Sponsor]

 

[Jadnashua]

What I would do is set the tub height so that once you've tiled it, the lip is just barely above the height of the finished surface with the tile (and backer) going underneath.

Generally, you'd have a layer of ply on top, then some waterproofing (maybe RedGard, or use a cement board with waterproofing on top of it), then the tile. Once all that was done, some silicone to seal the joint. You can't tile to the dimensional lumber directly without some stuff in between.

So, what do you intend to use to finish the surface around the tub in?

 

[Cavan Merski]

Thanks for the advice! My (wife’s!) plan is to tile over the ledge of the tub. I didn’t mention that because I thought it would be easier to explain in a more conventional approach. Our tile guy says he can build hardie up and over the rim, red guard it to high heaven and then tile over the rim but with the rim moving it will crack. I know this approach is unconventional (usually a single piece of stone on top) but we decided to go for it.

I’m pulling it out now to reset it in mortar with another few piles around the very front edges which cause the movement when you step near them.

my question still would be can I shim the rim of the tub 1/16th - 1/4” permanently after I set it again? I’m worried that the slight stress over time could crack the rim but also worried that the rim flexing on its own could crack my tile on top of the rim.

thanks again!

 

[Reach4]

a mortar bed

When I see that term, I get concerned. Look for past posts in this forum that contains

 

[Jadziedzic]

Have you reached out to Kohler technical support concerning your shimming question? They were quite helpful when I called with a question concerning a tub installation.

 

[Jadnashua]

Just be aware, none of the CBU manufacturers call for installation over flat, dimensional lumber. On the horizontal, they call for it to be over plywood because of the much improved stability versus dimensional lumber. It's one thing to screw it into a stud...it's another to do it over the flat. Plus, remember, all of them also call for installation bedded in thinset.

If you are planning cbu, and RedGard, and tiling over the rim of the tub, how do you intend to hide the inside edges? That would seem to be a problem. Tile onto the top of the tub rim won't bond great. You might consider something like KerdiFix there. You can get that in white.

You might consider putting a strip of wood underneath the cup of the edge. It might require a planer to get it just the right height so there's no possible movement of the rim. That would have enough surface area to support whatever you might consider doing on the tub. You might put a piece of plastic, or maybe even wax paper between the tub and the support block to help ensure it doesn't squeak if things move microscopically.

What are you planning to use to finish the edge of the tile facing into the tub? Cutting an polishing an edge of say natural stone is entirely doable, but labor intensive. I wouldn't try that with a ceramic. Many ceramic trim tile don't look all that good IMHO. There are some tile edge protection profiles that might work for you. Check www.schluter.com for their profiles. Some of them are designed to be bent to go around curves if that might help.