I have heard of using spray foam to insulate limestone or field stone walls. This is done because the irregular surface makes it difficult to put foam boards against them, right? Terra cotta foundations are also incredibly difficult to fasten or glue foam boards to. Especially if the foundation has bowed inwards, even just a little.

Has anyone had experience or ever heard about this? I would think that open cell spray foam would be preferable for an older foundation to allow moisture to slowly pass through allowing the wall to better dry, is that right? Open cell has a much higher permeability than closed cell, and since I don't have a sump pump or french drains or anywhere else for moisture to go, I need to make sure the wall can dry to the interior.

I'm looking to insulate my basement walls and it has proven to be a difficult task. I bought a bunch of foam boards only to find out that the surface of the terra cotta blocks doesn't like the (powerful) adhesives I tried to attach the boards. I also tried experimenting with some different drill bits but I think I'm going to end up just cracking and weakening the foundation and I don't want to do that. The foundation is old and brittle enough without me making it worse. Eventually a complete foundation replacement, including the floor, will be in order, but that is a massive and expensive undertaking that I'm several years away from considering.

Anyone have any thoughts about this?

If the foundation gets actively wet you may end up with moisture saturating the open cell foam. If you build a studwall that averages ~1-1.5" from the terra cotta you can use ~1" of open cell foam between the foundation & studwall, then use oversized low-density batts to finish out the R-value. This air-seals the foundation but still gives you about 1 perm of drying capacity. With the uneven surface using R19 batts designed for 2x6 framing stuffed into a 2x4 studwall minimized voids at the foam/fiber interface, and adds ~ R13 to the center-cavity R. With the foam, and averaging in the thermal bridging of the framing it comes in at around R18, give or take. Be sure to put something between the studwall bottom plate and the slab for a capillary break to keep it from wicking up ground moisture. (EPS or XPS foam board works.)