Should bathtub be set in mortar??

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Old 07-13-16, 05:01 PM
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Should bathtub be set in mortar??

Installation instructions for my new acrylic tub say it "must be supported along its entire bottom". They recommend using mortar as a bedding material.

This particular tub comes with a particle board bottom attached to it, and there are 2 1-inch 'legs' on the bottom of the particle board that run parallel to the length of the tub. These legs must go directly on the slab floor because they give the tub its pitch.

Is it common to set bath tubs in mortar? Is there any harm in not doing this? Can I use sand or other material instead? I have a cement slab floor that has been leveled.

Thank you.
 
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Old 07-13-16, 05:48 PM
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I know of three ways to do this, mortar, structolite (a kind of plaster) and low expanding foam. If the tub install instructions recommend mortar, that's what I'd use.

If it specifies it and you don't do it, your warranty will be void, and it will likely crack the first time someone heavy steps into it.
 
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Old 07-13-16, 06:48 PM
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IMO sprayfoam my be best but need to weigh tub down when applied... Mortar went out after the 80's after foam was invented..

Plaster I like to use but you need a lot ...
 
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Old 07-13-16, 07:03 PM
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Lots of types of foam at Home Depot. Great Stuff has a number of different types from the same manufacturer. Any brand or type in particular you'd recommend? I have Great Foam "Gaps & Cracks", will that work?
 
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Old 07-13-16, 07:06 PM
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Instructions say to use a 'bedding' and recommended mortar, but does not say you have to use mortar. I assume that means warranty doesn't require mortar. Maybe not? Thanks.
 
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Old 07-13-16, 07:54 PM
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Lite foam that dont expand much. Its just a filler
 
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Old 07-13-16, 08:06 PM
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I'd use the low expanding type sold for sealing around windows and doors. It doesn't expand as fast or as strongly as the normal type so is less likely to lift or stress the tub. Fill the tub part way with water before applying and you'll likely need a piece of tubing to extend the straw on the can far enough to reach the far side of the tub.
 
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Old 07-14-16, 05:39 AM
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"Fill the tub part way with water before applying"
This is confusing to me. To get the foam under the tub, that would have to be done before connecting the drain, right? Once the tub is in place, I have no access to either the drain or the area underneath the tub. How can you get the foam under the tub after connecting the drain? Or put another way, how can you fill the tub with water before connecting the drain? Are there any YouTube videos that show how to apply the foam?
Thanks. And one more question -- is it better to use plumbers putty or silicone caulk when installing the screw-in drain fitting?
 
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Old 07-14-16, 01:22 PM
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s it better to use plumbers putty or silicone caulk when installing the screw-in drain fitting?
Always putty...Period!!!!
 
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Old 07-14-16, 02:32 PM
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I've only ever used foam when there was access from unfinished walls to the area under the tub with the tub in place. If you're thinking of placing the foam through the drain hole, I don't think that will work. You won't be able to see what you are doing or make sure you have enough foam and good coverage.

If you use mortar or plaster, you place the material and then lower the tub into place. You can do that with no access from the walls. You have to be careful to not overfill the area...mortar or plaster will squish down a little, but not a lot. Better to have some peaks above the finished level and valleys below the finished level so when the tub is placed it will even out and fully support the tub. You should mark the walls at the finished height of the rim so you know the tub is fully seated and in the correct position.
 
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