How can I figure out what material my row home's interior and party walls are made out of?

Question

I'd like to hang some shelving on the wall in my kitchen that separates my home from my neighbor's. How can I figure out what material this wall is made of? The home was built in 1950. The party wall is completely solid if you knock on it with your knuckles and there's only one small metal object to be found with a magnetic stud finder; I'm assuming a screw or nail that was never cleaned up. It's smoothly finished and painted. Taking a hammer to it results in a lot of resistance and the tiniest indentation.

The interior walls are also sort of a mystery. I've hung two ceiling fixtures so I actually can describe them a little better: They're roughly a half inch thick, crumble when you try working on them and are hung directly to the joists in the ceiling. No lathes makes me think drywall but the crumbling makes me think otherwise.

This has always made it tough to do any work to the house. It's impossible to make a clean cut in the interior walls since they crumble and the party walls are very intimidating.

Answer 1

Sounds like plaster walls and the ceiling is gypsum boards covered with just a skim coat of plaster. My house in the midwest US has a similar setup. It was during a transition period (40s-50s) from lathes to gypsum boards so the walls have lathe and then rough and finish plaster but the ceilings have gypsum boards covered with a thin finish plaster.

To hang pictures and stuff, I typically start the hole with a drill to get through the harder plaster layer and then tap the nail in the rest of the way. For heavy shelves in the closets, I've drilled holes and used those plastic inserts you tap in with a hammer and then put a screw into.

Answer 2

There was a period through the 40s and 50s that gypsum wall board was used to replace wood lath in plastered situations. This evolved to doing a skim coat of plaster and finally , to just using joint compound.

Older drywall may crumble similar to plaster.

Your party walls may have been built with sound isolation channels, that is , metal strips that hold the two walls close, but make minimum contact, for better noise isolation. Insulation may have been added to further this effect.

Your safest course for adding shelves is to add a strip of wood on the opposite side of the wall, and drill pilot holes through your wall and use screws long enough to embed securely in your wood strip. Not the best, aesthetically, I know, but you can paint the strip wall color and hang a picture from it for disguise.