Priming and Sealing FAQs

Priming and Sealing FAQs


I want to apply a primer and then a finish coat of gloss to new pine skirting boards. Can you recommend anything?

  • Use two coats of Dulux Trade QD Wood Primer/Undercoat and then apply one coat of Dulux Trade High Gloss. Remember primer only comes in white so extra coats of a vibrant colour may be required.

  • "Hot" or "hungry" surfaces should be primed overall with very thin finishing coats of emulsion or Primer Sealer prior to painting.


What are the main reasons for paint staining and discolouration on plaster?

  • Past water leaks or burst water pipes can cause water staining. Before repainting, ensure that the leak has stopped and the surface is thoroughly dry, then spot prime the affected area with Dulux Trade Alkali Resisting Primer.

  • Heavy deposits of tar staining from cigarette smoke or soot staining around the chimney breast of open fires are common causes of staining, especially on water-based emulsion paints. To prepare, wash the surface thoroughly with detergent solution and rinse frequently with clean water. Allow to dry, then prime with Dulux Trade Stain Block Plus.

  • Conventional solvent-based finishes such as gloss can discolour with age, particularly in areas sheltered from natural daylight, this is known as yellowing. Prior to repainting, wash the surface with a detergent solution, rinse with clean water and allow to dry. It may be more advisable to use a water-based coating for a low light area.

  • Saponification occurs when oil-based paints are softened and liquefied by the alkali in plaster when moisture is present. Materials containing Portland cement or lime are strongly alkaline; gypsum plasters are usually not, but can become alkaline if gauged with lime or if it is brought forward from the backing during the drying phase. For these reasons, never use oil (solvent) based paints on plaster or masonry surfaces until they are completely dry in depth, then prime the surfaces with Dulux Trade Alkali Resisting Primer.Where saponification has occurred, completely remove the defective coating, wash down the surface and rinse with clean water. Allow to dry then prime with Dulux Trade Alkali Resisting Primer.

  • You don't need a primer at all. After a thorough clean, apply one coat of a solvent-based product, thinned 10 per cent with white spirit, followed by two full coats.


There are different solutions for each of these problems.

  • Staining caused by rust from old nails should be rubbed down to remove the rust, then prime any exposed metal with Dulux Trade Metal Primer before painting.

  • Resin bleeding from knots in wood should first be removed with white spirit. Then seal the knots with two coats of a suitable knotting solution and repaint.

  • All solvent-based paints such as gloss will discolour or yellow with age. To treat, wash the surface thoroughly with detergent solution, rinse with clean water and allow to dry before repainting.

  • If the wood appears to be dirty, particularly around glazing rebates, it may be affected by fungal growth. Clean the surface thoroughly and treat with domestic bleach, or Weathershield Fungicidal Wash, before painting.

Is there a simple way of dealing with powdery surfaces on outside paintwork?

  • Powdery or chalky old paintwork is caused by the paint film wearing away due to exposure to weather. This natural erosion of the paint coating can often be removed by thoroughly washing down prior to repainting. If washing doesn't remove a chalky surface, seal with the appropriate Weathershield Stabilising Primer before painting, or in severe cases remove the chalky surface entirely.

How do I deal with powdery internal surfaces?

  • Powdery and chalky surfaces are quite common in older properties that have been painted with distemper or white wash. You should completely remove these coatings by washing with warm water and a detergent solution. Rinse with clean water and change the water regularly. If the surface still remains slightly chalky, seal with Stain Block Plus prior to finishing.

Fetching the data, please wait...