View Full Version : High Density Foam

Michael Gabbay
10-07-2005, 11:19 PM
Ok so I'm almost done with my bathroom remodel. Ha Ha Ha Ha!!!

In 2 weeks I have a plumber coming out to help me set the tub. It is a fiberglass whirlpool, nothing fancy. The plumber suggested using high density foam to support the bottom of the tub instead of mortar. I called the manufacturer (Kohler) and they said that that would work just fine. So my question is what type of foam to get. The plumber mentioned the stuff that comes in the cans so I'm guessing its Great Stuff. They ake the window sealer and the crack filler. Does anyone have an idea of which to use? Or better yet, is there another type of foam I should be using.

Thanks, Mike

Jim Becker
10-08-2005, 10:57 AM
I'm having trouble trying to picture how you would use spray foam to "support" the tub. Can you be more descriptive? Are you sure they don't mean sheet foam to bring the base of the tub up to the same level as the mortar under the tile?

Ian Barley
10-08-2005, 12:10 PM
Like Jim - I cannot see how this installation makes sense. The sprayed foam is quite capable of exerting enough pressure to misalign a tub if used incorrectly. If you have been told to use this by a plumber I would say that he is also the best person to give further advice and clarification.

Jamie Buxton
10-08-2005, 12:43 PM
I'd imagine he's talking about the kind of foam that is intended for insulating small spaces in wall framing -- like the gaps around window framing. It comes out of a pressurized can very much like shaving cream. When it first came on the market, the foaming action was strong enough to bow framing lumber and make the windows not work properly. Nowadays you can buy similar stuff with low expansion. You probably don't have to fill the entire gap between the tub and the floor either -- just some isolated blobs. Because they're isolated from each other, the foam can squeeze sideways as it expands instead of lifting the whole tub.

Plastic foam, spread over a large area, can support surprisingly large loads. For instance, it is fairly standard practice to insulate underneath concrete slabs used for residential floors. The insulation is sheet foam. The concrete guys just put it down and pour several inches of concrete over it.

Michael Gabbay
10-08-2005, 7:27 PM
Basically here is how it will be used. The tub is set in place and hooked up to the drain and tested. Once satisfied, you spray the foam uber the tub. The tub bottowm does not sit on the floor but is supported by 4 feet. The foam or mortar is used to support the whole base of the tub so when you sit in it it does not sink/bend.

I was hoping not to have to call the plumber and as the experts here! ;)


Lee DeRaud
10-08-2005, 7:39 PM
Just to reinforce what Jamie said: make sure you're using the foam with the less-aggressive expansion.:eek:

Ken Garlock
10-08-2005, 8:29 PM
Michael, I wouldn't mess with the foam. You want something that is solid and will support the weight of the water and at least one large person. Insulating the tub is a far second to supporting the tub bottom.

Stop by the borg and pick up two bags of concrete mix. Slide them snuggly under the tub, cut a slot near the top of the bag, and add water. The paper bag will hold the concrete mix in place until it has time to set. It is a lot simpler than messing around with an unknown. :)

Richard Wolf
10-08-2005, 8:59 PM
I think the foam sounds like a great idea. I have always seen plumbers use plaster of paris to support the tub. I really don't think which foam you get matters, I think I would use the larger expansion type. There is so much room under the tub it will have plenty of room to expand.


Michael Gabbay
10-09-2005, 7:23 PM
Thanks guys for the feedback. It's not that I need or want to insulate it is for support. The beauty of the foam is you can dry fit the tub and then quickly set it once you attach the drain. The plumber said that this is standard practice.

All I have left to get finished before the tub goes in is a couple of trim pieces, grouting and making a template for the faucet cutouts/holes. I should be able to get that done by next Sunday.


Bill Lewis
10-10-2005, 8:20 AM
I'm with Richard on this one. Contrary to what others have suggested I'd use the high expansion foam. We're not talking about a small gap here. there's plenty of room for the foam to grow without lifting or shifting the tub.

I would not use foam board, it would squeak when the two surfaces rubbed. You could use foam board to fill in some of the gap, ut be sure that it is adhered to the subfloor too (that squeak thing again).

Lee DeRaud
10-10-2005, 10:27 AM
I'm with Richard on this one. Contrary to what others have suggested I'd use the high expansion foam. We're not talking about a small gap here. there's plenty of room for the foam to grow without lifting or shifting the tub.I'd use what the installer/manufacturer recommends.:D

The difference between the low-expansion and high-expansion foam is how much "air" there is in the final cured product, and that translates directly into load-carrying capacity: the high-expansion stuff is "fluffier" and will not support as much weight. May not matter for this application, but I'd want to know first, because you'll only get one try at it.:eek: