How good a paint job looks and how long it stays in good condition depends largely on the preparation of the surface to be painted.

General preparation requirements:

  • remove or repair any areas of the surface to be painted that are damaged, rotted or corroded
  • if large or long cracks have developed in cladding, or you have any other reason to question the weathertightness of the building, call an experienced building surveyor to see whether any other repair work is required
  • small holes and splits should be filled and sanded
  • replace fixings that are damaged or corroded
  • thoroughly clean the surface to remove dirt and contaminants, including:
    • rust: remove with a very light sandpapering – do not use a wire brush – then apply a zinc-rich primer before overcoating
    • mould:use a solution of 1 part household bleach to 4 parts of water or a proprietary cleaner; apply liberally, leave it for half an hour, then rinse surface thoroughly with clean water
    • resin bleed from timber: scrape and sand hard resin off, or use a solvent such as turpentine if resin is soft; once resin stops coming to the surface sand back bare timber, prime with alkyd-aluminium primer and repaint
    • efflorescence (salts that have come out of masonry): first, identify and stop any water entry to the masonry; when the wall is dry brush the white deposits away and wash the surface thoroughly
  • remove all loose or flaking paint
  • in many cases (for example, older weatherboards, or textured finishes) waterblasting is not recommended as it may allow water to enter behind the cladding or may damage the cladding surface
  • where paint is to be applied over an existing clear finish, remove the clear finish
  • for painted surfaces – especially around windows and doors – scrape off all the old paint after every fourth or fifth repaint 
  • sand the existing surface to remove gloss or chalking on the existing paint, smooth rough edges and remove sharp corners from boards. Brush off the dust after sanding to leave a clean surface.

For external painting of textured finishes:

  • wash down with a low-pressure chemical wash
  • remove loose paint with a stiff-bristled nylon brush.

For external clear finishing:

  • remove both the old coating and the weathered layer of timber directly beneath the coating, finishing the preparation and recoating without delay.