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WoodmanFL 12-03-2011 11:02 PM

New jet tub, set in a mortar bed or not?
Hi - I am underway with a bath remodel and am adding a new jet tub. The sub floor is the concrete slab and the tub has a built-in slope to the drain. It will be a three wall alcove set up and I want to know if I should set it in a mortar bed or not.

AndyGump 12-03-2011 11:47 PM

I use plaster, I understand it has fewer caustic chemicals in it than a Portland cement.


plumberinlaw 12-04-2011 01:41 AM

Some manufactures say to use expanding foam. Don't use too much you don't want to lift the tub.

joecaption 12-04-2011 05:53 AM

And what does the manufacturer instrutions say? Follow there directions not one's given here. There the ones that are guaranteeing it.
I just can not imagine how any form of foam would work, it compresses, and you have no control over how much it's going to expand and might just lift it up off the floor.

WoodmanFL 12-04-2011 09:38 AM

The instructions just say "add bedding compound to fully level and support bottom of tub.". So what is the best method to do that? If mortar, then what kind should I use?

oh'mike 12-04-2011 10:22 AM

Masons mortar works fine----Press the tub into the mortar bed and attach to the wall--

Don't add water to the tub--or step onto the tub to press it down--you will compress the mud to much--and when the tub is drained--or your weight is removed--the tub will pop up and have a hollow under it-----Mike----

rjniles 12-04-2011 12:43 PM

I use a bag of latex modified thin set mortar. (Like used to lay tile.)

WoodmanFL 12-06-2011 04:03 PM

Sounds good. Thanks for the advice!

Michael Thomas 12-06-2011 04:27 PM

Re: Foam tub supports:

FWIW, some manufacturers now allow minimally expanding structural foam as a support, for example Jacuzzi specifies support by "The use of materials that provide a level installation are allowed provided the method used will insure a level bath that is supported from the bottom. Materials that may be used are a floor leveling compound, mortar, plaster or minimal expansion structural foam having a density of a minimum of 5 lbs./cubic feet".

I have discussed the use of "Great Stuff" when used as a tub or shower floor support with Dow Technical support, and their response is a definite "Not Recommend" as: 1) the density (2.2 lbs/cu/ft for the standard product and 1.3lbs/cu/ft for the "Pro" product) is too low, 2) no "Great Stuff" product can be guaranteed to cure properly when used in this type of "spread-out" application, and 3) that such products are not intended for structural use (for example, they may not expand back to original cured volume after repeated compressions).

The bottom line is that that the use of such products as support or re-suport tub and shower floors is approve by neither the plumbing fixture manufacturers nor by Dow Chemical. Such foams are not "structural" products, and even if such repairs are initially successful they may not be durable.

As for alternative materials, far as I have been able to determine there is no site applied 1 part (non-mixed) structural foam product available for this use.

So while I'm not saying it won't work, if the tub is not supported "per manufacturer's installation instructions" might find yourself in this situation.

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