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We were trying to put in some laminate flooring, and as I was vacuuming against the base of the drywall I noticed that dirt kept falling from what looked like inside the wall. The drywall seemed a little flimsy here, so I decided to cut a hole and find out what was behind there.

Surprise!

Dirt in the wall???

Sketch: enter image description here

Our house was built in the 70s, and my wife was searching and found people making suggestions about sand and mortar and things of that nature being used to level the tub, but this is nothing of the sort. It's a very fine dirt - the same that we have in our yard. Inside the hole is the drain for for the tub and the copper water pipes. It smells damp - like under a house. Our home is a one story slab home, and this is a metal tub.

I looked for signs of critters (ants, termites, that sort of thing) but it doesn't look like there are any tunnels. It's very loose dirt. I've probably removed about 2-3 liters of dirt.

Why is this dirt here? Should I put it back? Remove it?

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  • What is on the other side of the wall?
    – DMoore
    Dec 23, 2015 at 6:09
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    Definitely expose more of this. It won't make it any harder to repatch the dryway. Moist dirt is NOT appropriate in contact with drywall or framing, especially not as it will make a virtual termite highway. Expose this, and repour what's needed to restore the integrity of your slab.
    – Bryce
    Mar 22, 2016 at 19:47

4 Answers 4

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The dirt you have removed is probably from around the tubs drain pipe. When the slab floors are poured all the plumbing has already been installed. When pipes protrude from the floor the contractor builds a walled surround that keeps the concrete away from the pipes. This is due to: 1) it is easier to have space to position a pipes' final connection and 2) depending on the alloy's used the alkalis' in the cement can corrode the pipe. If you enlarge the wall opening and using a flashlight you should see the tubs overflow and drain pipe going straight down into this dirt you excavated. Another possibility is the one you mentioned; it was fill dirt used to level the cast tub. Building codes aren't specific regarding what material to use when leveling a cast tub, as long as it is leveled and stabile. If the soil isn't in contact with any framing members and isn't annoying you leave it. If you feel more comfortable without it inside your walls than open the wall and remove it in 5 gallon buckets. Don't remove any dirt from under and close to the tub bottom. Watch for plumbing if you excavate.

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    The pipes most definitely went down through the dirt - but they went into the slab. Would that make a difference here? Also there was no "wall" on the other side, it just emptied right into the space under the tub... I guess you'd call it a skirt? The top and side part of the tub. Dec 23, 2015 at 14:09
  • So inside the wall you can see a large amount of dirt?
    – ojait
    Dec 23, 2015 at 15:58
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    I've added a bit of a sketch to my post. The dirt was piled on top of the slab in between the drywall (which was a bit soft/corroded - the inside paper was gone) and the tub itself. It was definitely in contact with the 2x4s in the wall. My other thought is maybe it was moles? I thought slab foundations went a bit deeper than typical mole burrows though... Dec 23, 2015 at 16:58
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    I'd estimate about 3-4 gallons of dirt that was piled up and around there. Dec 23, 2015 at 16:59
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    I agree with the fact that dirt is used to protect and align the pipes in a slab, but many slabs are poured on a vapor barrier or rock bed. That would have me looking for other evidence of some type of pest that may have been making a nest I have not seen settling cause this kind of intrusion if the earth is dry but have had to cut a slab when the copper pipe corroded because beach sand was used to bed the pipes and it ate the pipes causing leaks and we had a mud volcano in the wall. I have not seen dirt used to level a tub but it all needs to be removed.
    – Ed Beal
    Feb 9, 2018 at 23:14
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Chipmunks can sometimes cause this problem by discarding their tunneled dirt. Just a possibility. I would check for entry points.

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  • Pocket gophers do this but not chipmunks, at least not this amount of dirt. I posted photos of some of my jobs, hope this helps. Feb 17, 2023 at 6:43
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I see this post is an old one but it’s possible you or others may be dealing with the same issue, which I do deal with all the time in my business.

This is caused by pocket gophers. They follow sewer and water pipes and tunnel into homes, creating dens underneath the bathtubs, even inside the walls.

Opening the wall up and exposing your home to the mold spores, contaminated soil, feces and urine is concerning. This should only be done by an expert like myself with HAZMAT safety gear. Hopefully there is someone where you’re located that does this as well. The soil must be removed by buckets, secured and banded so it doesn’t spill inside the home, it’s like handling asbestos, you really must be careful. I don’t know where you’re located by when the soil is in the right conditions, it can go airborne and enter into the lungs of humans and animals, it’s called Valley Fever and I’ve had it since a kid. It can be fatal, which is why handling this dirt filled with urine, feces and rotting plant material must be handled correctly. I can’t be clear enough when I state this is dangerous, and I’ve not mentioned how gophers will attack and bite.

Once the soil is removed, all of the insulation, dry wall, and many times the lumber must be removed. If it’s a supporting wall or beam, you will need to bring in a structural engineer. Even before that, the gophers must be trapped and killed. Do NOT under ANY circumstances use any toxic or flammable gases like propane and carbon monoxide, especially carbon monoxide as it’s colorless and you already have tunnels open inside your home. The gas will travel through the porous concrete, through cracks in the concrete, around the gaps near pipes, into the wall cavities and those inside, pets or people can be injured or killed. The smaller the being, the deadlier carbon monoxide is. Trapping is the only “true method”, you’ll see a dead gopher and know it won’t be back…if there’s only one. Odds are there are more than one. These dens are created by the females and the more generations, the bigger the problem. You also must know they carry parasites and serious diseases, even the fleas on them can carry bubonic plague, so hiring the right person to correct this is paramount.

Once the gophers are trapped and killed, those entry points must also be corrected. Spray foams, slurry’s, steel wool, wires, none will suffice. The gophers can chip away at concrete, removing those products is simple for them.

Pocket gophers are strict Herbivores and will not consume poisons or baits, regardless of what anyone in the industry tries to claim. I have removed gophers from inside the studs of walls and pulled out arsenic, strychnine, warfarin and flares packed tightly into dirt balls made by the gopher. Typically they will move them outside or aboveground where kids, pets, domestic animals, wildlife and birds can consume, it’s typically birds which will take flight, fall to the ground flailing in pain, attracting predatory birds, wildlife or pets that eat the poisoned bird and they are also poisoned.

I strongly suggest a visit to your family doctor and ask to be tested for Vally Fever, regardless of where you live. Testing for mold inside that space on the rooms adjacent to the bathroom is also needed as mold travels and grows quickly. Also, get checked for parasites and any rodentia specific parasites/diseases, including tapeworm.

I wish I could give you DIY tips but I can’t and won’t because you and your family of anyone moving into it needs to be safe and if it’s not don’t correctly, it can be real bad later on.

Gophers inside bathtub cavityContaminated soil inside the cavity under bathtub brought in by gophersgopher created a vertical tunnel and den system inside stud cavity in exterior wall

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  • In our case it was definitely moles - our dog actually caught one above the surface. Feb 19, 2023 at 18:47
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Fascinating!

Total conjecture - but if its in the bathroom walls, then maybe it could provide sound insulation (if there was a lot of it). Filly the walls with dirt would do that very well and cheaply!

Might also provide thermal insulation - again if filled. Dry loose dirt isn't great insulator - but it can help.

Finally it might buffer humidity - but who knows why.

Unless I was trying to do something with sound - I'd take it out.

Ohh, it also might be used to dampen noise from pipes (or do something relating to insulating them.) Are their pipes in the dirt?

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    WHAT???...we don't put dirt in walls...EVER. And we don't want it left there either. Remove it. Yes, the plumber probably left a block out in the slab for the pipes and the dirt around (in) the block out is left exposed...but we don't use dirt in a wood frame wall for insulation, sound barrier, or anything else. If this is located on an exterior wall, a rodent may have gotten in and tried to make a home (dig up the dirt around the plumbing blackout). If it smells "like under a house," it could mean the slab is under-cut by a rodent and they are pushing excess dirt up and out of the way.
    – Lee Sam
    Feb 25, 2017 at 9:57

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