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!
Sketch:
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?
Best Answer
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.