Use white ash. Soaking the white ash in advance is the key. Remember, it’s not about adding table salt.

Okay, let’s start talking about chemistry. 1. Stone (limestone caco3) is burned with fire to obtain lime, also known as white ash (also known as quicklime cao). The white ash is fully soaked in water to obtain lime paste (also known as slaked lime ca(oH)2), and this lime paste becomes sticky.

When painting the wall with lime paste, stir it to break up the precipitated lime paste. Lime plaster is applied to the wall and reacts with carbon dioxide in the air over several days. It becomes limestone caco3 which is as hard as stone.

When I used to paint walls, I was always misled into adding salt. In fact, soak the white ash one night in advance and it will stick.

Real white ash is too cheap, and merchants make too little money, so it is almost impossible to buy pure white ash now. Most of the white ash sold on the market has glue added, which is also the reason for the production of formaldehyde. But it is really convenient to use, just add water and you can brush it.