Have a northeast home built circa 1910 or so that has a first-floor bathroom jutting out a few feet past the foundation. Lately I've noticed some digging going on by an animal. Looking closer, I can see that the material under the aluminum siding--what looks like cement board or weatherboard (with some kind of wire mesh) and wood--is rotted away. I was able to hand-loosen about 8 inches from above the soil, and now there's a nice-sized gap about four feet wide in which I can see inside. (There's batt insulation visible.) The rot likely came from a wonky gutter (since adjusted) on the overhang, and/or some roots from a nearby tree.

This is the view while I'm on the ground. The top jagged board is right under the aluminum siding, and that wood piece came off in my hand. Beyond that is just a void, then the batt insulation.

enter image description here

So how can I fill this? There's a concrete base under the soil so I think I can basically connect the top cement board (not really sure what it is) with the bottom layer with concrete, but I think I need some kind of backing element for that. Should I mortar in some brick, and then spread concrete over that? And should I worry about moisture from the concrete getting inside and under where the shower is? TIA.

  • 1
    probably a bit easier to understand if you sketch a basic section drawing showing the various elements in the wall assembly. Sep 5, 2023 at 5:00
  • 1
    that picture and the description are confusing, that is why you do not get any answers
    – Traveler
    Sep 5, 2023 at 6:22

1 Answer 1


It's hard to understand what's going on from the picture and description. But if the wood has rotted, presumably the mud plate, it was to be replaced. If the foundation is fieldstone and the mortar crumbled away, new mortar must be added. If animals are getting in, wire mesh is the solution.

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