Walls are heavily chalked, no new construction

Hello good evening I have an apartment and the walls chalk very much The painter who assessed this said he would have to treat these walls with a special fixative (keim) Honestly, I do not know it but whatever My question to the professionals Is this special fixative necessary? Does this fixative need to be painted on (like with primer) or sprayed so that it penetrates well into the pores Thanks for the initial advice

If the fixative is from Keim, you normally have a mineral substrate underneath. Then the fixative is "water glass," silicic acid, and other such terms. It ensures that the substrate becomes silicified, i.e., crystals form. The process should be completed within 2-3 weeks inside an apartment; crystals do not form overnight. Do not apply it to glass! It also silicifies there, meaning splashes from any mineral materials, which would also include, for example, tiles, natural stone, or terracotta, will not come off again. Simply painting over is completely sufficient. It is transparent, flows like water, and you cannot see it... except if you apply it to places where it should not go. If there are dirty spots on the wall, these will also be embedded into the crystalline structure. Repainting later is no problem. Since many painters have never actually ordered anything from Keim, I assume he knows what he is doing.
Still, check what is in the fixative.

Best regards
Gabriele

Thanks for your response