This is caused by painting over contaminated surfaces such as wax, oil or polish. The paint cannot adhere to the surface and draws away leaving unpainted areas. This can also be caused by contamination on the brush. Putting it right Intended for use with emulsion paints, water-based undercoats are vital in many cases for a smooth finish. Most of the options within the UK will also function as a primer, effectively offering protection for the underlying material and an adhesive surface for painting in a single coat. Acrylic Primer Undercoat

Depressions or surface blemishes in the paint film. A common cause is rain that has fallen on the surface before the film has had chance to fully dry. Putting it right This is usually caused by contamination of the underlying surface by soluble stains. Putting it right This is a common occurrence in new houses and is often the result of plaster drying out or movement of the building. Putting it right

When the surface is thoroughly dry the affected surface will need to be rubbed down using 'wet and dry' abrasive paper. It can then be re-coated.

Using the wrong type of roller can cause foaming of a paint film. Sponge or foam rollers should be avoided with water-based paints. Long pile rollers must be wetted out properly. Foaming happens when air gets into the wet paint film to create air bubbles. When these bubbles burst craters are left on the film surface. Sometimes these craters dry to give an even film. Putting it right It is important to seal the original stain by applying a coat of Polycell Stain Stop prior to re-decorating.Oil-based undercoat paints are for use with oil-based finishing paints. While these paints were traditionally the choice of professionals, advances in water-based options mean that today many will use both, or have moved to water-based entirely. It’s worth keeping in mind that oil-based undercoat paints will release volatile organic compounds (VOCs) while drying, which can be dangerous. Ensuring adequate ventilation is crucial, with many opting to use water-based paints internally. Water-Based Undercoat Allow the surface to dry and then rub down using 'wet and dry' abrasive paper and a solution of warm water and detergent. Once rinsed and dried the area can be repainted. If your colour choice is much darker or lighter than the original, apply a primer to help your new paint colour adhere better to the surface.