spongy bathroom floor

[reilym]

I thought I remember reading about this topic, but I can't find it. The floor in my PW Lexor's bathroom is molded plastic and it's fairly rigid, except for one spot between the toilet and floor drain. It gives me the heebie jeebies every time I step there and feel the floor flex. Anyone else have this problem and have a solution? It would help if I knew how these floors were installed, but it looks like it would be difficult to remove it to add additional support.

I was contemplating using a rigid expanding foam injected into a hole drilled into the 2" vertical threshold below the surface of the floor, with extra holes to allow the foam to escape (see attachment). It would be relatively easy to fill the holes after the foam cures. Thoughts?

[booster]

Originally Posted by reilym

I thought I remember reading about this topic, but I can't find it. The floor in my PW Lexor's bathroom is molded plastic and it's fairly rigid, except for one spot between the toilet and floor drain. It gives me the heebie jeebies every time I step there and feel the floor flex. Anyone else have this problem and have a solution? It would help if I knew how these floors were installed, but it looks like it would be difficult to remove it to add additional support.

I was contemplating using a rigid expanding foam injected into a hole drilled into the 2" vertical threshold below the surface of the floor, with extra holes to allow the foam to escape (see attachment). It would be relatively easy to fill the holes after the foam cures. Thoughts?

You have to be really careful with expanding foam as it has a lot of force when in expands. It easy will sheet rock off a wall if you put in to much of the canned stuff. I used to support the new bathtub I put in quite some time ago, and it worked fine, but I had full access to the open back so I could watch it foam and not overfill. I was very surprised the short distance it flowed before setting up and only going up. I also had the tub full of water to keep it from getting lifted off the floor. The "normal" procedure for doing a shower floor like you are looking at would be multiple holes and a long hose on the nozzle so you can push it all the way to the rear and extract it as you release the foam. It will never get to the rear going in at the front a couple of inches even if you have a vent hole to let the air out. Probably 4 holes across the front and fill half way from the rear on the first pass and let it expand toward you for a few minutes. The do the front half. Make the holes quite a bit bigger than the nozzle to help air bleed and extra foam if it gets there. Stop injecting a few inches before you get all the way to the front and fill them later if it doesn't expand that far. If done with too much foam in could push the floor into a dome and possible pull the drain out. It might be a good idea to put a 1/8" sheet of somewhat bendy plastic on the floor and have some on heavy stand on it to hold it down.
I saw a repair guy do a regular plastic tub in a condo that kept cracking and he must have put in over 10 holes in the bottom of the tub and used fiberglass bondo over them, sanded, and the painted the tub with urethane two part paint. It turned out looking better than new and didn't crack again.

[dicktill]

There are different foams. I'd use the foam that is made for doors and windows. It is specifically formulated to not expand much and bind the doors and windows, so probably a better bet here.