Use of milk by painters...

[Externet]

Hello all.

Many years ago, saw painters (overseas) using milk to prepare their something, did not pay enough attention; unsure if was for a sub-base to walls or the finish paint itself.   Remember seeing a never-sanded glass-like smooth surface on walls before applying paint.  Perhaps that was the intention ?  How does it work, how come there is no bacterial degradation with something prepared with milk ?  

I do have search engines but not interested in proportions and preparation, but more on your chemical explanation part of it.

[Endy0816]

Not sure I can give a good explanation but you are talking about milk paint.

https://en.m.wikipedia.org/wiki/Milk_paint

Think it is addition of a Base to casein protein, though not sure on the chemistry involved.