Bathtub Replacement

Old 10-19-22, 06:06 PM
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Bathtub Replacement

I am replacing a 47 year old cracked and chipped cast iron porcelain bathtub with a Acrylic tub. The house is a concrete slab foundation. When I research installation, it states to use a 30 LB felt pad, but they don't sell the pad and I can't find one. Are they talking about 30 LB roofing felt? I have also read to put down about an inch of mortar cover it with plastic and set the tub. This scares me because of the tub getting out of level or not seating properly on the concrete slab. Or to put small mounds of mortar cover with the felt. Others have said use Great Stuff Foam, but with the experiences I have had with this have not been pleasant I did not get the desired effect even though I was cautious not to spray much and it caused a lot of cleanup. I don't want the tub to squeak when you step in. I would appreciate any feedback.
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Old 10-19-22, 07:47 PM
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I can only say what I do, and that's what I would recommend...

30# felt (I often use Tyvek cuz I have lots of it) I put down first is just a bond breaker between the concrete floor and your mortar bed. The next guy to work on it will thank you when it comes up cleanly.

I mix a bag of sand mix (mortar mix) in a mud pan so that it's fairly dry... just moist enough to stick together in a dry ball when you squeeze it in your fist. Then I dole it out with a trowel here and there, about 1" high, on the tub area... leaving voids in between the piles, so that the mortar has somewhere to go when i set the tub into it.

Then when I set the tub in, I give it even pressure, checking with a level in all directions and diagonally. Watch the front edge obviously to get close to the subfloor... but its not usually critical that it be down tight on the subfloor as your final floor material will usually cover up any mortar showing underneath.

Fasten per the mfg instructions... most flanged tubs have hold down clips.

Then once you are satisfied, hook up the drain and fill it with water to the overflow, and let it sit that way for a couple days.
Old 10-20-22, 05:20 AM
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I too do the mortar method. I don't know how you think it will cause the tub to get out of level. You set the tub in the mortar while it's still wet and it squishes to conform to the bottom of the tub to provide even support. After setting the tub in place I will walk inside the tub a bit or place a moderate amount of weight to make sure the mortar squishes out and is not deforming the tub. After it hardens it actually helps prevent the tub from moving and getting out of level because it is well supported by something that can't move.
Old 10-20-22, 02:04 PM
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Drywall mud is sometimes used and if it needs removal later would seem easier to remove than concrete.

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