Primers seal surfaces prior to painting. They make a non-porous base and reduce the amount of paint needed to create a perfect finish. There are several types of primer but they generally fall into two categories: oil based and acrylic primers. Oil-based primers are available in different formulations for wood, plaster and metal and are used before an undercoat is applied. Acrylic primers, on the other hand, not only dry faster but can also be used as a primer and undercoat on bare wood and plaster. Because they are water-based, acrylic primers will, however, raise the grain of wood, which will then need to be sanded down.

A good sealer for porous or dusty surfaces can be made by mixing PVA with water - follow the manufacturer's recommendations with regard to quantities. Damp stains can be covered with a proprietary stain block available in both brush-on and aerosol formulations. While these effectively obliterate damp stains, they will not cure damp, so always make sure that the cause of the damp is treated first.

• You can buy emulsion paints that protect against mould, since they contain a fungicide. Anti-condensation paints are also available, containing tiny glass beads that act as insulators.
• Thin polystyrene sheets can be used to line very uneven walls.
• They iron out bumps and reduce condensation.