The functional effectiveness and durability of the entire coating system depend to a large extent on the correct choice of primer. This is because the primer protects the paint from aggressive constituents in the wall material. These include alkalis and salts. Examples of commercially available primers include consolidation, impregnating and penetration primers. There are differently formulated products to suit the various types of substrate, so you can always choose the right primer for the job at hand. They combine the following properties, which may be more or less pronounced:

• Consolidation of old, friable substrates
• Good penetration
• Regulation of absorbency
• Adhesion promotion for subsequent coatings
• Pigmentation
• Insulation against aggressive constituents in the wall material
• Creation of a hydrophobic zone under the coating

You can choose between aqueous and solvent-based primers. Aqueous primers are better for the environment, but usually do not penetrate as deep into the pores of mineral substrates. This is because of the water’s surface tension and the binder particles contained in the water.