Noticed some/most walls of our 1952 house are about an inch thick and look like they're made up of two layers. About 3/8 of one texture and then about 5/8 of another, no lath to be seen. Is this two layers of drywall for some reason, or plaster over drywall? Was this common? And what would be the best method for patching - 3/8 and 1/2" screwed together and then mud to make the difference?