How are Most Bathtub Supported? - Remodeling and Home Building Answers 

Structolite is plaster and can be found in most big box stores in the bag mix drywall compound area.

I like that idea....better to be safe than having a chemical bleed through the plastic. Thanks

Great to hear!

Mortar... Yes

When in doubt follow manufacturers recommendations

Great idea!!

Sounds like a handyman did the install that did not know what they were doing.

I've always used them, except for cast iron tubs. Check with the manufacture to make sure.

Do you put ledger on all 3 sides or just the back, long side (like in the video)?@@homebuildingandrepairs3122

When you used ledgers, did you put them on all 3 sides or just the back. @@homebuildingandrepairs3122

I know this is late... but might help someone down the road. The mix of mortar used to support a tub is (or should be) very dry (It's called dry-pack) and therefore will not damage the typical wood subfloor. Whether or not you want to add something under that mortar ( a piece of roofing felt, or housewrap, or even 6-mil poly for example) to act as a bond-breaker between the subfloor and the mortar is a different issue. Dissimilar materials are going to expand/contact at different rates... it cannot be prevented. Rather than have the mortar/plaster bed crack because it's bonded to a subfloor that is moving seasonally... or break that bond and allow it to float in one piece is arguable... I'd rely 100% on manufacturer's recommendations so you don't void your tub/shower warranty. BTW - Portland cement-based mortars are caustic and could potentially damage fiberglass/acrylic tub units. I personally think plaster of Paris is a safer alternative for bedding a tub, but the right answer might also be "nothing". It really depends on the manufacturers' instructions. Don't use a bedding compound of any kind if the mnfct. says "no". And NEVER use expanding foam. If you're going to use a spray-in-place foam product make sure it's minimally expanding. I've seen expanding foam put enough pressure on a tub bottom to crack it, and/or lift the unit off its shims. Hope this helps.

Thanks and you're welcome.

I think most mortar mixes are one part cement and three-part sand, but if you wanted to be stronger you could always mix one part of cement with two parts of sand.

The mix should be weaker, not stronger, and as dry as it can be. Just enough Portland cement to provide a little structure is all that's required. In fact, you can use perfectly dry play sand with no Portland cement at all to bed a tub/shower.

I did tub repairs and installations for over 20 years. That's exactly what I did and recommended to people especially if they were installing a drop in jetted tub. Often the tub jetting systems develop leaks and need repairing. With a piece of visqueen or sheet plastic it keeps the mortar from sticking to the bottom and allows it to form to the tub like a shoe for easy removal and re-installation.

I don't see anything wrong with the idea as long as it doesn't form any type of container to trap water, if there is a leak.

You're welcome and thanks for watching.

The building should be designed so that the weight sitting on top of the floor will be transferred throughout the building and eventually to the ground through concrete footings or a concrete foundation. Let me know if that didn't answer your question.

Thank you for responding. Yes I think so! I have a new master bathroom w/ shower, 70gal whirlpool bath, tiling stone, and possibly 1-3 people made me look into it. I found a few online discussions that made me consider the fact the deep whirlpool tubs may lead to the need for additional support than what is standard...

watch this video: Biggest Problems Created When Using Mortar Under Bathtubs - Plumbing potentially that mortar shrank and when pressure was applied while standing on the bath it moved back down on mortar bed which caused the problem. I am not an expert but I believe it's better to use cement base tile adhesive instead of mortar in such cases. Or simply let the bath sit on its legs if it has them. Use poly glue to secure the bath in place to the supporting frame and there won't be a need for mortar bed. Anyway get your warranty claimed, though might be installer's fault.

I don't know for sure what the problem would be, but I would contact the product manufacturer. If you want, you can always send some pictures of it and you can get our email information on the website.

It would be an excellent way to retain heat, but most of the foam I have seen expands and could damage the bathtub if it expanded too much. I've actually used fiberglass insulation or insulation they use for walls around bathtubs, but couldn't really tell you if it makes a big difference or small difference.

homebuildingandrepairs hey i have a very old house built in 1897 needless to say its not level, but running into the bathtub problems it is an inch out of level how should i fix this and what is my best option. i have a 1964 cast iron 30 inch tub i could use but i want a new tub but do not know what to go with in my situation. please some advice would be great

+Tony B - Urethane foam does, indeed, insulate the tub. I replaced a worn-out cast iron tub about 17 years ago with a porcelain glazed steel tub, and before installing the tub, I flipped it upside-down, poured two-component urethane foam all over the bottom of it in small batches and then trimmed away the excess. The foam doesn't provide mechanical support, but it keeps the water comfortably warm for 30-45 minutes, making it great for soaking. I think it would be great if tub manufacturers encased the bottom of their tubs in foam insulation at the factory.

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You should find what you're looking for here, let me know if you don't. www.homebuildingandrepairs.com/repairs/bathroom/index.html

I've never seen a felt pad used, but contact the manufacture for more information.

Sorry about that and thanks for letting us know.

Back it up or park it up

If it will fully support it, but won't form well under tub like mortar.