Acrylic 3-piece tub/shower.

I'm new here and was wondering if someone could answer a few questions I have about installing one of these in my basement.

The floor in the area where the tub will be sitting is out of level by less than 1/4" from the left to the right of the tub. As I understand it, these tubs are designed to sit on the flange at the front and then are supported only by the two legs on the back side of the tub. My question is how to level it properly on the front side as my instruction manual states not to shim it in this area but they do not give any indication as to what I'm supposed to do.

I'm thinking I will take my belt sander and just trim the left side of the flange a bit as this is the high side of the floor. This should give it a nice stable base I would think. There is approximately a 1" flange about 3/8" of an inch thick along the bottom of the front side which it is supposed to sit on.

Another question I had is what to do about the mounting flange that attaches to the rough framework around the entire alcove. The flange on the mid section is warped about 1/4" or more and is going to take a fair bit of coaxing to get it to fit up tight. The instructions call for #8 wood screws to be used to secure it to this frame but I'm afraid that it might crack the flange itself. The manufacturer tells me it will be fine but I was looking for some other experienced opinions.

Thanks in advance for any help.

What, if anything, does the manufacturer say about bedding the tub in mortar? Fully supporting the entire bottom of the tub makes it feel much more substantial when stepping in and it gives you the opportunity to make it level. You don't want it being supported by the interior flanges with the feet off the floor, but you do want to support them, usually with a ledger board screwed to the walls in the alcove.

It would be interesting to know how many tubs end up sitting on nothing more than their decorative skirts and a couple of poorly-attached stubs of 2x4 underneath, but like Jim has essentially said, you definitely want more than that!

gardingh said:

The floor in the area where the tub will be sitting is out of level by less than 1/4" ... My question is how to level it properly on the front side as my instruction manual states not to shim it in this area [and does] not give any indication as to what I'm supposed to do.

I'm thinking I will take my belt sander and just trim the left side of the flange a bit as this is the high side of the floor. This should give it a nice stable base I would think. There is approximately a 1" flange about 3/8" of an inch thick along the bottom of the front side which it is supposed to sit on.

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I did something similar in my own basement, and shaping that skirt will work just fine. What I did was to place the tub in its corner and level it up all around, then I used a thin 4" grinding wheel resting lightly on the floor to cut the tub's skirt to match the contour of the floor. You could possibly do as well with your belt sander, but you will be risking damage while flipping your tub around a lot, and you will likely spend a lot more time getting the process completed. And in my own case, I actually already had the tub set when I did that cutting, then I slipped the vinyl flooring through that gap and in under the skirt. With the actual bottom of your tub sitting on a proper foundation, it is not necessary (and actually better, I believe) that the skirt not bear all the weight of tub, water and occupant(s).

gardingh said:

Another question I had is what to do about the mounting flange that attaches to the rough framework around the entire alcove. The flange on the mid section is warped about 1/4" or more and is going to take a fair bit of coaxing to get it to fit up tight. The instructions call for #8 wood screws to be used to secure it to this frame but I'm afraid that it might crack the flange itself. The manufacturer tells me it will be fine but I was looking for some other experienced opinions.

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The manufactuer likely says some cracks in that area "will be fine" because they are presumed to be "caulked and covered" by the surround. It sounds to me like your tub got pulled from the mold a little early, and I would be careful about pulling that warped flange back to frame. It would be a good idea to add some nailers between the studs and behind that flange, and to then pull it back a little at a time with galvanized (as in "rough-surfaced") roofing nails or fast-thread, treated decking screws through pre-drilled holes maybe 3-or-so inches apart.

Here is exactly what it states.

Leveling:
To provide additional support, improve soundproofing and facilitate leveling, it is recommended that a layer of mortar or plaster be applied to the base of the bathtub legs, and covered with a 1/16"(2mm) polyethylene sheet. The layer should be thick enough to facilitate leveling of the unit without raising it. Once the unit is in position, ensure it is level in both directions for proper draining.

Leveling must be done under the wood legs located beneath the unit. Do not level directly behind or under the flange at the front of the unit.

The entire bottom of the tub is sitting on 3/4" plywood with two little 3/4" plywood pads on the back side at each corner. That is where they indicate that the shims or the mortar is to be placed.

They don't say anything about setting the entire thing in a bed of mortar but I think that might be a better way to go. The instructions do not call for a ledger. The only support given by the walls of the alcove is some wood blocking to stiffen up the surround walls, and the flange which rests against the framing on the outside of the opening.

Here is a link to the installation manual. It is the top PDF link.
http://www.maax.com/en/TechSupport/InstallManualsDetail.aspx?CodeCategorie=B&GammeID=5&TypeProduitID=3&ProduitID=532

That manual is identical but worded differently than the one I have and it sounds like the plywood base is designed to sit on a bed of mortar rather than just the "legs". Sorry this is a little long winded but I appreciate the help.

You are definitely understanding the issues, and now you get to decide!

And for some additional perspective here ...

Old-style cast-iron tubs sit on nothing more than some decorative legs with heavy point-loads both on tub bottoms as well as whatever kinds of floors, and with nothing else supporting the bottoms of those tubs' bowls.

Now fast-forward a half-century or so ...

The typical fiberglass tub comes with a skirt along one side and some stubby legs at the other ...

What is the difference? Did the manufacturer under-engineer?

Some do better than others, but plastic always "gives" just a bit more than does cast iron. If cast iron could flex, it would also need more support.

I have a new tub I intend to set in another week of so that I believe has enough built-in support to be just fine without anything additional underneath, and maybe you have something similar. Nevertheless, I believe we will each be better off if we make our tubs feel just as solid in their bottoms as do those possibly-over-engineered-to-last-forever cast-iron oldies.

Thanks for the help, I still have the tub sitting loosely in the rough framing with the other two pieces in their proper locations just to see if it will fit with the measurements in the manual. I think I will talk to the manufacturer tomorrow and see what they say about setting the thing in a bed of concrete as that will ensure it is well supported. Now about the concrete, I have read that anything with a high sand mix will work fine. I have a bag of 6000psi ready mix, will this stuff be just fine? Or should I get something different? I plan to Lay down a sheet of poly, pour a bed of concrete on it, then another sheet of poly. After this I will set the tub on it and ensure it is sitting where I want it, then I'll brace it in place and let it set up. Any other tips about doing this that I should know?

topping cememt


Normal finishing cement --sand mix works great

Setting the tub in concrete makes the tub feel like it is cast iron....

just make it a little extra wet so you can shake and set the tub down into it and it will work great

If you put some ledger boards on the walls under the lip, making sure that they are level, you can use them as a guide when pushing the tub down to seat it. You don't want to end up pushing it down too much on on side then trying to pull it back up - that would likely create a void which you are trying to avoid.

gardingh said:

Now about the concrete, I have read that anything with a high sand mix will work fine. I have a bag of 6000psi ready mix, will this stuff be just fine? Or should I get something different?

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I think the stuff you actually need is going to say "Sand Mix" right on the bag. Also, you need to figure out how much you will need. The bag will include info as to its yield, and that is usually around 1/2 of a cubic foot. If you were to pour a spot that was ultimately 4" thick x 24" x 36", that would be 2 cubic feet from at least 4 bags. Also, you will want your mix fairly stiff (closer to peanut butter than to molasses) so it will "peak" or "sit as a lump" and not puddle out all over the place, and you should avoid the typical gravel mix (like your bag of Ready Mix) and only use sand since you will not be able to do any "floating" or vibrating to get the large aggregate to sink below the surface rather than remain there to later work against the bottom of your tub. You could use your bag of Ready Mix first and put your Sand Mix on top of that, and you might even consider a short form made out of 2x2 lumber to help define and maintain the pile you are building a bag at a time ...

... and all of that is why I instead simply build and use a taper-fitted framework made from pressure treated lumber to support the bottoms of tubs that already have flat bottoms.