Grooves on a lot improve glue captivity.

3. First you should prepare the wall. Generate large irregularities using a cement mortar, and on top and small cracks and irregularities should be covered with putty. The finished surface should be as flat as possible, you can check the condition of the walls and angles using the rule. Before the putty dries, go through the entire surface with a gear spatula to create furrows. Grooves on a lot improve glue captivity.