Plumbing problem, bathtub cracking. How to fix?

January 11, 2019 3:53 PM

My bathtub was not properly set on the ground. When I stand in the basin, it creaks and feels like it's giving way. I can see, from a crawlspace, where it's unsupported. How can I fix it?

Images of the problem are here: https://imgur.com/a/CmS7Cr8

I bought a house. About a month into living here, the basin of my tub started to give way. When I step on it, I can feel it move at least a few millimeters up and down.

The fiberglass tub sits (from what I can see) on a partial bed of expanding foam. I did not install it.

Think about the basin as if it's broken into thirds, lengthwise. On the outside two parts of the basin (where the bottom begins to curve up both sides), it does not give when weight is applied. This is where the foam supports the basin. But in the center third, there is no support, and when I stand on it, it creaks and I can feel it give way. I assume it will begin to crack soon.

There's a central location in my house that contains nearly all its plumbing. The rest of the house is basically a U-shape that surrounds that area. From inside the crawlspace, I can access the pipes that lead to the shower head, nozzle, etc., and the front part of the tub; that's where I took the images.

The foundation of the house is concrete. Single-level. There is no basement, so the tub is resting (somewhat) on what appears to be a combination of concrete, dirt, and foam.

Can I fill that gap with some type of foam? Will it be strong enough? (Even if possible and recommended, this will probably be a logistical nightmare because of the cramped space.)

The people who worked on the rest of the plumbing were clearly lazy and either didn't have the knowledge or didn't care to do it right, so I wouldn't be surprised if the foam holding the tub is *also* a bad idea but happens to be working better than the support of nothing at all. (We've had to fix a few other pipe-related issues already.)

If I have to tear out the tub anyway, what should I do? Would mortar work on its own, even with the large hole (see images) where the drain pipe goes into the ground? What about plywood, wooden slats, or some combination of the above?

Any recommendations would be helpful. I'd appreciate advice from the non-experienced to the professional, but please point out who you are.

Given proper instruction, I'm confident in my ability to repair this myself.

posted by mr_bovis to Home & Garden (10 answers total)

A bath shouldn't be supported that way at all. Normally a bathtub will have a rigid base board, either built in or glued on, then a metal frame that provides the main support. You then build a timber frame that adds extra support around the edges. A few blobs of foam don't really cut it. It sounds like the tub may not have a base board, and is only held up at the ends.

Baths generally sit just above ground level, raised a few inches on the frame. Yours looks almost as if it's been set into the ground. It I wanted to fix this properly, I'd take the bath out, clear out and level the space, then do it using a proper frame. This might require a new tub.

I suppose as a temporary fix, you could wedge something under the middle section, and throw a bit more foam at it...
posted by pipeski at 4:21 PM on January 11, 2019 [3 favorites]

It's a bit tough to tell what kind of access you have to the unsupported area (photographing crannies like that in a coherent way is really hard, I am literally a professional construction-cranny photographer and I still struggle with it) but my first thought would be to basically shim it up. Wedge some wood in the gap, tight enough that it won't just fall out and over as broad an area as possible. Then if it didn't move anymore I'd basically just call it a day at that point.
posted by Anticipation Of A New Lover's Arrival, The at 5:34 PM on January 11, 2019 [2 favorites]

FWIW, the previous owner of House the Sequel did the same thing when he installed the tub. I discovered this when the tub began ripping away from the wall, which was not desirable. As the next (competent) plumber discovered, the uneven support actually caused the tub itself to warp slightly.

Answer in my case: rip out tub, start over again.
posted by thomas j wise at 6:22 PM on January 11, 2019

IAAA, IANYA. I specialize in construction QA - mostly commercial stuff, but I've rehabbed a few residential properties on my own.
OK, poke your finger into the foam and tell us if you think any amount of that stuff has the compressive strength to do the job.
First photo: Is that soil on top of the slab, which would mean soil touching the wood framing in photo 3?
In photo 3, left side, if looks like termite damage on the board the plumbing clamps are fastened into. Soil against lumber is in almost every case a code violation, and something termite treatment companies will tear up a contract over.
Photo 3, left side. Two supply pipes, one marked with a "C". Presumably for "cold". Other pipe looks to be the exact same color. Cold water can be run in PVC (very white appearance) or CPVC (slightly yellow tinge). Hot water *must* be run in CPVC if using PVC type pipe - as opposed to pex flexible and other new-fangled systems. You have PVC type pipe.
There should be no "hole around the drain pipe". You should not have open communication between the soil under the house and the interior of the house. Typically the plumbers stub up and the concrete gets poured around the pipes. Then the plumber comes back and "trims out" - makes the connection between the pipe and the fixture.

There should be a vapor barrier (plastic sheet of some kind) between the underside of the slab and the soil. I do not see that in photo 1.

Were it me, I'd get the thing out of there and fix the substrate properly. And get the soil etc off that lumber, and let the termite treatment guy come in and hose that area with termiticide.
Then go back and set the thing according to what the manuf. recommends. Most of them are going to be about the same.
I will say I had to set a fiberglass shower on a sloping wood floor (old second floor porch). I threw down some 6 mil plastic, mixed up some of the fine aggregate concrete (redi mix et al) sort of stiff, and set the shower pan in it and tapped/wiggled it down till level. 20 odd years ago. It hasn't budged and is still solid as can be.
posted by rudd135 at 6:35 PM on January 11, 2019 [13 favorites]

Also, PVC and CPVC pipe is labeled with black print at intervals along the length. You may be able to spot these labels.
posted by rudd135 at 6:40 PM on January 11, 2019 [1 favorite]

Response by poster: To answer your questions, rudd135:

The foam isn't solid, but I can't poke my finger right through it. It's probably tough enough to hold up the tub. I don't notice any give when standing inside the tub basin on the parts that sit atop the foam. I expect that, if the entire basin was held up by the foam, I wouldn't be in this forum. I also don't know how long that foam will last and stay as rigid.

The pipe you mentioned is all CPVC.

The material touching the framing appears to be concrete. What you see in photo 1, directly behind the pipe and below the tub basin, is rock hard.

I had a termite inspection before moving in. The inspector cleared the house. Maybe it was damage from long before I moved here?
posted by mr_bovis at 9:02 PM on January 11, 2019

4x density foam you can't poke your finger through this very structural tough closed cell stuff.
posted by hortense at 11:36 PM on January 11, 2019

When we bought our house is we also had an awful creaky tub - a look in the crawlspace looked similar to yours, a crappy mortar base that was crumbling. Several contractors said the only fix was to tear it out and reset it. We lived with it for a few years until we did the renovation and finally got it set properly. FWIW the tub never cracked over the course of use in several years.
posted by Karaage at 5:07 AM on January 12, 2019

You mentioned it started after a month and that you had some pipe issues. Is there a chance that any of those issues eroded soil or foam support that had been there? You say the stuff beneath is hard like concrete, so maybe not.

I'm not an expert, just a homeowner, but I also wonder whether rodent barrier mesh around that giant hole might be $6 well spent. (I'm not sure how easily that hole area connects to outdoor space.)
posted by slidell at 7:03 AM on January 12, 2019

At Home Depot they sell small sheets of about one inch thick insulating foam. They were about 2 feet by two feet. If you could cut the size you need to do the central support job, sandwiching layers until you are there or close enough that spray foam will finish. Tite bond blue glue would hold together layers. This is a twenty dollar solution. My tub was once dropping away from the bathroom wall due to a bad joist. I used a car jack to get the joist, and tub to the right height, and installed a standing 4x4 to make it all work. Then I repaired the wall and matched the tile so it was all nice again. I bolted it all together and all. For a basement like that I would favor the least possible intervention until you have to dig. Then spend some money.
posted by Oyéah at 11:38 AM on January 12, 2019