Shower Project

[ss3964spd]

Will keep my fingers crossed for ya regarding that PT 2X4 pony (knee) wall cap, Mike. In any case you do not want to adhere your granite cap directly to the PT 2X4. You'll need to screw some kind of backer to it first, and water proof the seams were necessary.

I'm guessing you mean Kerdi, not Ditra.

I think it was mentioned before, but per Schluter you cannot adhere Kerdi directly to dimensional lumber.

[eagle4x]

I have an indoor jaccuzzi tub that holds about 80 gallons of water. I originally put sand to support between the floor and the tub, but I'm not satisfied with using the sand. I removed most of the sand and I'm considering either:

1) Mapei flexcolor CQ premixed grout...put in 2.5 gal. ziploc bags. I have many buckets of this that I wasn't able to sell on ebay.

2) Some pieces 2" thick rigid foam insulation.

Which option would be better?

[Gozo]

Can I put in a vote for neither?
80 gal of water gets heavy and fiberglass has a limited flex before it gives up. You might get away with either 1 or 2 for a while, but why tempt fate?
If you have some access, you could put a mortar bed under that tub. Would spread the load over a wider area and would last forever. Another option (similar to your 2nd choice) would be to use a ton of expanding foam under the base. Same thought as the mortar but would have a bit more give to it and be a point load like a foam block. I might lean that way if there was only a few inches of leeway to maneuver with.

[Davy]

I'm voting with Jeff but you have to be careful with expanding foam. A plumber did one for me that raised the tub up too high and I had to tear it out and start over. I like the mortar idea best.

[jadnashua]

Spray foam comes in at least a few different configurations. If you go that route, use one designed for sealing around windows as it doesn't expand as much, so would be much less likely to stress the tub and try to move it. Some become rigid, some are more flexible. The rigid ones can pulverize when stressed.

[Davy]

I might add that the tub I mentioned was filled with water to hold it down to the tub deck but the drain didn't seal off well so it was slowly seeping without anyone knowing. It all drained out during the night and was 1/2 inch up off the tile deck in the morning. The plumber said it was triple expanding foam. It definitely would have had a better chance of staying put had the water stayed in the tub. But I still avoid the foam that's made for wide gaps.