Bathtub levelling conceptual error

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Bmusgrove

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This question is just for my own learning. I've read a many ways to level the tub.

I have a Bootz Maui cast tub with a foam support pad under it. The instructional video says the foam pad should be in full contact with the sub floor, but then says to use wooden shims to level the tub if it is necessary. The tub is 3/8 out of level side to side. If I place3/8 shims on the back side (ledger board side) the foam will no longer be in full contact with the sub floor. The weight will now be on the foam shim interface and the apron.

What Am I missing? Somewhere I am making this too complicated

Keep in mind I am the type that prefers a 9 inch bolt and 8,000 Ft Lbs of torque when instructions call for a 3/8 bolt and 5 inch Lbs of torque...o_O
 
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Jadnashua

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DOes the tub sit level if the floor is level? You could level the floor before installing the tub. In a typical tub, say 30x60", that's 1800sqin, but with the flange and tapers, maybe 1500 of that might sit on the floor. Take 300# of water, 250# for the tub, and maybe a #200 person, you'd have 750#. 750/1500=0.5psi. Conversely, say the area of the shim is maybe 3x5" and you put in five of them, you'd have 750/75=10psi, a big difference. Now, some of that would be sitting on the opposite edge, but still after it compresses, you'd still probably have 10x more pressure on the foam. There are some floor patching compounds that could be used to level the floor., or if you could live with it being a bit higher, use the technique of a bunch of piles of mortar, then smush the tub down into it. You won't have full coverage, but you'll spread things out much more than some shims. Or, tear off the foam and use the mortar - the CI tub is more than rigid enough to be supported by those distributed piles of mortar rather than a full coverage of foam.
 

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You might do a search for self leveling compound. I am not experienced, but I suspect that could be good in this case.
 

Jadnashua

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You might do a search for self leveling compound. I am not experienced, but I suspect that could be good in this case.
SLC, when used over a wooden substrate, generally (most, not all) require a minimum thickness (usually 1/2" above the highest point), and metal lath to help reinforce things - you can only do a feather edge over a slab or CBU. IOW, over a partial floor area to the stated depth, not a great idea. But, there are floor patching compounds that can be used in that circumstance that can be run to a feather edge and bond directly to wood. Sometimes the data sheet requires very careful reading, as many will say it can be applied to a feather edge, but in the fine print or details, talks about on a slab verses different requirements over a wooden subfloor.
 

Bmusgrove

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The floor is mostly level :). I did have to remove the existing 3/4 OSB and level it out and the floor is level front to back , side to side and diagonally within 1/16 over 4 feet. The tub pad is probably the cause.

I contacted the manufacturer and their tech said do not use shims. I was correct in my thinking that it is not the best way. Use mortar under the pad instead. Use shims to find the level, lift the edge of the tub and work mortar under the foam to just a little deeper than the shim thickness needed, then set the tub back down squishing it into the mortar until level.

So I will set the level using shims. mark my teddies for a ledger board, lift the tub, install the ledger then put 1/2 or so of mortar down in the footprint of the foam.

Glad my brain questioned their online instructions vs what made sense and what I was reading. now... Any recommendations for mortar or will any decent thick bodies MORTAR (not aggregate cement) work?
 

Jadnashua

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Do not try to build a full-contact, flat, layer of mortar...you will almost certainly fail. This is the reason why I asked if the tub sat flat if the floor was level. Given your observation that it is the foam that is off (crappy factory quality control, IMHO!), you still want decent coverage, and you're more likely to achieve that with some piles of mortar. A flat layer, with the weight/area, means it will be very hard to impossible to compress things to get your tub level. Some small piles mean more pressure to smush things to the desired position. Some people use deck mud...a mix of 3-5 parts sand to one part Portland cement, mixed with just enough water so it will hold its shape if you compress a handful (like a snowball), but not drip water. Excess water might seem useful, but it makes things weaker, and also increases the amount of shrinkage. Some people like to use Structolite. Some plastic on the wooden subfloor will keep that from drawing too much moisture out of the mix, which can also weaken things. Given it is cast iron, the foam might add some insulation, but many CI tubs are supported by just four small feet. YOu could remove some foam in appropriate areas, and use mortar, and not have the foam sit on the floor at all.
 

Bmusgrove

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Do not try to build a full-contact, flat, layer of mortar...you will almost certainly fail. This is the reason why I asked if the tub sat flat if the floor was level. Given your observation that it is the foam that is off (crappy factory quality control, IMHO!), you still want decent coverage, and you're more likely to achieve that with some piles of mortar. A flat layer, with the weight/area, means it will be very hard to impossible to compress things to get your tub level. Some small piles mean more pressure to smush things to the desired position. Some people use deck mud...a mix of 3-5 parts sand to one part Portland cement, mixed with just enough water so it will hold its shape if you compress a handful (like a snowball), but not drip water. Excess water might seem useful, but it makes things weaker, and also increases the amount of shrinkage. Some people like to use Structolite. Some plastic on the wooden subfloor will keep that from drawing too much moisture out of the mix, which can also weaken things. Given it is cast iron, the foam might add some insulation, but many CI tubs are supported by just four small feet. YOu could remove some foam in appropriate areas, and use mortar, and not have the foam sit on the floor at all.


Its a porcelain on steel not cast iron :) not that it makes a difference as far as procedure goes.

Didn't intent to try and build a full contact flat layer. That would be difficult even for a pro, especially when your foam base may not be flat and parallel. I would build a low ridge (only need3/8 of a inch on the low side) of fairly dry mortar front to back, possible biased towards the low side and lightly set the tub in it then cuss yell and wiggle it to level it. A few bags of sand or mortar bags in the bottom until it drys. The procedure appears to be fairly straightforward.

Is there any suggestions on brands to use or stay way from? I am mor likely to go to the big box stores such as Home Depot.
 
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Jadnashua

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FWIW, I'm not sure I'd consider a porcelain on steel tub. Thought you'd said CI. Your tub will want a good support bed. Still, though, piles verses trying to make a flat surface will work better with a better chance of getting it level with a semi flat screed.
 
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