exterior paint preparation boys play next to pool

Preparing before painting is key to a great exterior finish.

Nothing beats a great paint job, especially one you’ve done yourself. Give yourself the best chance at success by following these instructions.

What you will need

Before you start make sure you have the right tools:

  • Filler and Filling knife 
  • Sandpaper 
  • Dulux Prep Wash 
  • Sponge 
  • Wide paint brush 
  • Masking tape 
  • Drop sheets

Use filler and sanding to make the surface smooth

  1. Before painting, remove and replace any rotten or decaying timber.
  2. If your paintwork is already in good condition, a light but thorough sand should be sufficient. After sanding, the surface should be a flat sheen. To test if you need to strip the paint, cut with an “X” with a sharp knife and press 10cm of adhesive tape firmly across the middle of the cut. Remove the tape quickly. If any pieces of paint come with it, you will need to strip the loose paint off before applying the new top coat.
  3. Any areas of peeling must be fully removed by sanding. Areas that are cracking should be filled with exterior grade filler and sanded before painting. For metal surfaces remove any rust by wire brushing or sanding the surface and use Dulux All Metal Primer before top coat. Plastic down pipes and spouting need a clean and a light sand before applying paint. Before painting wipe or brush down any area’s to remove any dust.
  4. Fill any holes and cracks in your exterior surface with a high quality exterior filler. For weatherboard use Selleys® No More Gaps® Exterior & Weatherboard or Selleys® Plasti-Bond Heavy Duty where movement is likely to occur. For exterior masonry use Selleys® No More Cracks™ Exterior Brick & Render or ready mixed filler Selleys® Spakfilla® Heavy Duty on large cracks.
  5. Apply the Filler with a putty knife, overfilling to compensate for shrinkage as it sets.
Quick Tip

Quick Tip

If you have a lot of sanding to do consider using a mechanical sander.


  1. Brush clean any surfaces, clearing away dirt and cobwebs.
  2. Thoroughly wash the walls with Dulux Prep Wash to remove grease and dirt. A high-pressure cleaner and bristled brush can make the process easier.
Quick Tip

Quick Tip

Some common timbers contain high levels of a staining material called tannin. These tannins can migrate to the timber surface via moisture. If you are using tannin rich timber, be sure to wash the timber thoroughly with Cabot's Deck Clean and apply an exterior top coat like Weathershield with tannin blocking properties.

Masking the area

Masking before you paint makes the job faster and cleaner.

  1. Use a good quality masking tape along any edges you don’t want to paint, including trims or windows.
  2. Push the edges of the tape down firmly to ensure straight edges.
  3. Remove the masking tape at a 45° angle before the paint dries completely. If the paint is too dry, the masking tape can rip the paint film when it is removed.
  4. If the paint dries before the tape is removed, using a sharp blade, score the edge of the tape before removing so that it doesn’t pull paint away from the wall.

Undercoats and priming

If you are covering a dark colour or a surface that’s never been primed or painted, you will need to use an undercoat. It can also provide a better coverage and hiding power than just applying extra top coats.

To apply an undercoat simply paint one coat of Dulux 1Step Prep after preparing the area. If your topcoat is oil based use Dulux1Step Oil Based Primer, Sealer & Undercoat instead.

If your substrate is particularly powdery thoroughly wash the surface with Dulux Prep Wash and seal with Dulux PRECISION Sealer Binder.

For metal substrates use Dulux Precision All Metal Primer to provide additional corrosion protection.