It mostly depends on the type of concrete surface you are etching on. Generally speaking, it can take up to 30 minutes for a surface to be etched and 10 days for the surface to be ready for paint.
The longer the etching mixture of muriatic acid and acid stays on the surface the better, because it will help to reduce the moisture levels and alkalinity. Without the etching procedure, the paint will not adhere to the surface. It will peel off and might sink into the surface rather than stick over the top of it, so the color will be weakened.
All concrete surfaces need to be etched before painting, regardless of how new or old they are. In fact, new concrete surfaces will need to be left with the etching mixture on the surface for even longer than old concrete. New surfaces will need slightly longer than 30 minutes for the etching process to be completed, because these surfaces are the most smooth and need longer to roughen.
The important step after etching is cleaning away the acid. This is usually achieved by washing the surface with a neutralizing solution (usually 4 parts baking soda to 100 parts water if the etching product doesn’t come with a neutralizing liquid). This should take 4 days to settle into the surface before standing on the floor, and up to 10 days before painting on the surface.
A self-etching primer is a useful product that takes about as long as regular muriatic acid to prep the surface before painting. However, for the best results, you should use muriatic acid and do the etching process properly.
It mostly depends on the type of product you use when etching. Each product will have its own instructions and directions for the etching time before you can paint over the surface, so it’s best to follow each product’s guidelines.
It also depends on the environment of the surface. You should etch a concrete surface, whether it’s a wall or floor, when it’s raining outside as this will wash the acid off which will only lengthen the process.