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.


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?

  • What is on the other side of the wall? – DMoore Dec 23 '15 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 '16 at 19:47

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.

  • 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. – Wayne Werner Dec 23 '15 at 14:09
  • So inside the wall you can see a large amount of dirt? – ojait Dec 23 '15 at 15:58
  • 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... – Wayne Werner Dec 23 '15 at 16:58
  • I'd estimate about 3-4 gallons of dirt that was piled up and around there. – Wayne Werner Dec 23 '15 at 16:59
  • 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 '18 at 23:14

Chipmunks can sometimes cause this problem by discarding their tunneled dirt. Just a possibility. I would check for entry points.



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 '17 at 9:57

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