Why there are chalking when touching the wall? You would never touch the walls are left white chalk in your hand. It is called calcification or chalking on the walls. This is one of the damage layer of paint on the walls.
There are some things that cause calcification occurs. One of them is the quality of the paint is not good. Paint is not good in general has a concentration of resin or binder is low. However, it can also occur in good quality paint is diluted too much.
Paint the wrong placement will also make the same thing happen. In general, the interior paint is applied to the exterior will also experience calcification.
To fix this, you need to scrape the entire layer of paint to the surface of the substrate or your wall. After that, apply a good quality paint. Nowadays, a lot of paint that are ready to use without the need to be diluted further. Use the paint so that the paint is not one of concentration.
Another important thing, use paint as intended. Do not use paint that placement is not appropriate.
Make sure when doing the painting substrate surface is dry, clean and free from other debris.