ᐅ Walls show strong efflorescence; not a new construction.

Hello, good evening
I have an apartment and the walls are chalking a lot.
The painter who assessed it said that these walls need to be treated with a special primer (Keim).
Honestly, I am not familiar with this, but it is what it is.
My question to the experts:
Does it have to be this specific primer?
Does this primer need to be applied by brush (like a primer) or sprayed on to penetrate well into the pores?
Thanks in advance for the advice.

If the primer is from Keim, it usually means there is a mineral-based substrate underneath. This primer is a "water glass," silica solution, or similar product. It causes the substrate to become silicated, meaning crystals form within it. This process typically takes 2-3 weeks indoors; crystals do not form overnight. Do not apply it on glass! Silication also occurs there, so any splashes on mineral surfaces—such as tiles, natural stone, or terracotta—will not come off. Simply painting it on is sufficient. It is transparent, runs like water, and is invisible unless applied to areas where it shouldn’t be. If there are dirty spots on the wall, these will also be embedded into the crystalline structure. Repainting over it later is no problem. Since many painters have never ordered anything from Keim before, I assume this person knows what they are doing. Still, take a look at the ingredients in the primer.

Best regards,
Gabriele

Thanks for your reply