ᐅ What type of plaster is this? Basement renovation

Dear forum members,

I would like to paint my basement with silicate paint. Unfortunately, I do not know which plaster was used as the base layer, and the previous owners don’t know either. The stone is supposed to be calcium silicate brick. Can you help me? Is there a way to find this out?

Thank you!!!

In terms of color and appearance, it could be gypsum mortar. Just try to check if you can easily scratch into it. Or wet it and see how it absorbs water.
There are also white mortars based on cement, which are harder.

Pure silicate paint usually does not work well in this case, but the substrate is relatively unimportant for a dispersion silicate paint. It generally adheres well to any mineral substrate without problems.

Can you scrape it off relatively easily with a knife? Then it is gypsum plaster. If it is rather difficult and the surface feels slightly sandy, it is likely cement plaster.