Tub de-leveling for drainage

[Belegedhel]

I am rebuilding the shower/tub assembly in my '73. The original tub and seat had to be rebuilt from the outside using fiberglass to make up for all of the damage that 40 yrs had done. In addition, the drain on the tub had to be moved from the right near corner to the left near corner.

All of this work has resulted in two issues:
1) I need to create a new "base" for the tub to rest on that will create a small slant from the right to left to help ensure the tub drains (this is opposite of the original slanted base that the tub sat on, and no, that base can't be flipped around reused because the tub is not square.
2) The underside of the tub is no longer completely flat due to the sloppiness of my fiberglassing, and the need to build up certain parts of it in thickness to fill the old drain and create/reinforce the new drain area.

So I thought that the easiest thing to do would be to flip the tub over, create a "form" around it using duct tape, and then to pour some kind of self leveling compound onto the bottom of the tub. If set at a slight angle, then I would accomplish getting a flat bottom surface as well as building my draining angle at the same time.

The problem is finding the right self-leveling material. The stuff they sell at the big box stores for correcting your subfloor before putting down hardwood or tile is a masonry-like substance, whereas I was thinking something more plasticy would be ther right way to go.

Any suggestions?

[DaveMc]

How rigid can foam be, I wonder? Similar to spray foam. That way you shave/sand down excess? Probably want to figure out if open vs closed cell is a better idea, but the foam seems like it would give even support under the shower pan.

Just a wild idea to help gin up other ideas...

Dave

[Boxite]

Create a mass of corrugated fiberglass matting that you can sit the shower pan onto while it's still wet, positioning the pan in the amount of levelling you desire...then let the fiberglass mat cure overnight.

[Belegedhel]

Thanks for the suggestions!

I had given the spray foam some thought, but was really hoping to find something that would self-level, so that I wouldn't have to manually smooth/angle it.

The suggestion of creating a corrugated fiberglass mat could work as well, my only concern there is to make sure I get consistent support, as I would hate for the miserable thing to end up cracked after all the work I've done on it. I do have some polyester resin sitting around that turned out to be not the right stuff for the tub repair project--it occurs to me that if I were to mix up a quart or so of that stuff and pour it on as a self-leveling layer of maybe 3/16" at the high end of the "wedge," it might work fine. The big unknown is how much shrinkage to expect from that stuff.

[JCWDCW]

Might sound a little wacky, but plumbers mix up a bag of concrete and dump it under Whirlpool tubs just before setting the tub in place, to give support to the flexible bottom of the tub. Might work for you; simple, but adds some extra weight. You just have to support the tub in place while it cures.
JCW

[Belegedhel]

Yes, I think this is close to what I would be accomplishing if I tried using the "self leveling" stuff that they sell to address subfloor irregularities, as it is a cementish sort of stuff. I worry about both the weight and the brittleness of it--afraid that it would fracture over time, and eventually end up rattling around under the bathroom cabinetry.

[55AS]

How about a 1/2" sheet of high density plastic (think cutting board material), planed down to form a sloping surface? Not cheap, but you can buy it in 4x8 or 4x4 sheets...

[ijustlee]

I would build a wood frame that made contact at 4 points that gave you the slope you want and then make a criss-cross pattern of spray foam to press the tub down into. Do this for the final install as it will be glued in place very well! You could have it on top of a thin piece of plywood in case it ever has to come out again. After you push the tub into place I'd fill it about half full of water because the foam will continue to expand for a while and could lift the tub.