Expanding foam to shore up whirlpool tub bottom?

[mnRemodeler]

Hi All,

So I installed a whirlpool tub yesterday. I put down 120 pounds of masonry mix to set the tub in. It didn't seem like enough to me but it sounds like 90 - 120 pounds is the going rate. I put down tar paper on the sub floor, added the cement and then put a 4 mil poly barrier over the top of it. Then I set the tub. I did have to push the tub down into the cement.

I have the front open so I can see under the tub. I noticed that I don't have any cement in the corners or around the drain which is the area in which people will step into the tub. Not sure if the motor is supported either though this tub has metal rails that the motor sits on.

I was wondering if I should get some spray cans of low expanding foam, hold the plastic up and then shoot some foam in the spots that don't have support?

Not sure if I'm over thinking things but now is the time to do it because once its all buttoned up it's too late.

I have heard that foam can lift a tub...but not sure if the low expanding foam would do that.

What do you think?

 

[mnRemodeler]

Did some research and most spray foam is not made for structural support. I bought mortar and will use that to fill in the corners where it could use more support.