Setting Vikrell Tub in Mortar

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Old 11-03-16, 03:36 PM
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Setting Vikrell Tub in Mortar

I have a Kohler Sterling Ensemble Vikrell tub and the install instructions specify either installing the tub on a felt pad or setting in "1-2" of mortar cement". There are no further notes about this process. I've read dozens of various forum inquiries about setting tubs in mortar and still can't come to a conclusion on best practice. Some say use structo-lite instead of mortar, some say put plaster sheeting underneath and/or on top of the mortar.

Vikrell tubs are made of a hard plastic like material and have a grid/lattice base for the tub. Anything you set the tub in will get pressed into this lattice structure.

I do like the idea of having a plastic barrier between the mortar and tub so that removal doesn't have to be destructive, but that prevents there being any bond. To me, mortar is a bit too rigid a material be setting plastic in, also it doesn't seem like it would stick to a smooth plastic. I think something more like a polyurethane construction glue (more flexible) would be better but I don't know of a material like that which you can make a bucket of.

Any thoughts about what is the best method and why?

I did call Kohler today but apparently after business hours...
 
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Old 11-03-16, 03:53 PM
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The setting bed, regardless of the material used, is for structural strength. It does not need to "bond" to the tub although such bonding is not a problem. It prevents the bottom of the tub from flexing due to the weight of both the water and the person within.

I have a PearlBath (by Maax) true whirlpool tub I installed some ten years ago. It specified a mortar bed but when I did it I found that setting it on a solid mound of mortar hoping it would spread the mortar out for full support AND have the tub rest on its integral legs was impossible, at least for me. I then scraped the mortar down to just slightly less height than the space between the floor and the bottom of the tub. Setting the tub on its feet I then used sticks, trowels and whatever to push the mortar under the tub and around the legs until everything was solid.

I'm glad I did it. That tub is absolutely rock solid and has no flex whatsoever, even with my obese body in it. I doubt it will ever crack, something that would have been a distinct possibility with any kind of yielding bedding material.
 
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Old 11-03-16, 09:39 PM
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Seems to me if the mortar used isn't sticky then even the slightest settlement of the mortar will mean that it is not contacting the tub bottom. The you'll still have movement.

Ok, given that mortar is used there are still questions about application. Like the plastic sheeting I mentioned - above, below, both? If no plastic sheeting, I've read of some people 'buttering' the bottom of the tub first, then setting in in more mortar to ensure good contact.

What kind of mortar? Type S, type N, sand mix? I recently used modified thinset to set a vikrell shower base but that didn't require a very thick bed.

Here's what the bottom of my tub looks like. Ignoring the lattice the subfloor to tub space varies from 1 to 2"
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Last edited by chimpywrench; 11-03-16 at 10:01 PM.
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Old 11-04-16, 11:32 AM
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I called Kohler again today to get their official recommendation and the call was dropped after being on hold for 10 minutes
 
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Old 11-04-16, 02:20 PM
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Sorry, I can't answer your additional questions. With that "waffle grid" bottom on your tub it will most definitely stick tight. I don't see any way that placing plastic sheeting between the tub and the mortar bed will be possible. I know that some people use a plastic sheet between the wooden sub-floor and the mortar but I don't see any real point in that other than to keep the mortar from bonding to the floor, which in my opinion is kind of defeating the purpose of the mortar.

Nor do I see discrete "feet" on that tub. It doesn't appear that there is any way to set the tub and then push the mortar under it like I did with my tub. Maybe the contractor members that have done several tubs have some better answers.

Okay, looking at the picture again I see it has lots of little feet so it could be possible to push the mortar under it but I think it would be a hard job to actually fill the area. Then again, the waffle grid probably strengthens the bottom considerably.
 
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Old 11-04-16, 02:34 PM
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Well I did finally talk to a Kohler rep and she could not advise using one type of mortar product over another. She did say not to use thinset because it will break down over time. She also advised using sheeting both below and above the mortar bed to make removal easier.

I think I'll just buy some Type S because that's what I'm used to using for projects and do 4mil plastic on the subfloor then 1mil on top so it'll conform better.

Will report back after I'm done!
 
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Old 11-04-16, 03:52 PM
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I also have a sterling unit, 5' three piece shower. It also has the mortar or felt pad options. I could not see the mortar install going well so I inquired about the felt pad, blur box. He said they didn't carry them and couldn't get one. OK? So I did more searching looking for "why". It seems the reason for either was to eliminate squeaking from the many feet on the floor. That would answer why the felt pad was included as an option.

In my opinion and with my base unit, support is not a problem. I picked up a furniture pad that will fit my space nicely and I'll secure that to the floor making the install much easier. That project has been on hold while finishing exterior work.

IMO, it seems strange that a company as big as Kohler would let a little issue like this go without a simple solution.

Bud
 
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