Hi @swmw,
Because the timber has already been coated with a deck stain, some preparation is required before painting it white. You cannot paint straight over the stained surface and expect a durable result. The timber will need to be cleaned and lightly sanded, then sealed with a suitable exterior primer before applying your white topcoat.
Start by cleaning the timber thoroughly. Use Cabot's Deck Clean to remove surface dirt, dust, mould, and any residues left from construction. Rinse well and allow the timber to dry completely. Once dry, use 80-grit sandpaper to lightly sand all stained surfaces to dull the finish and create a good key for the primer. You do not need to sand back to bare timber, just scuff the surface evenly. Remove all sanding dust before moving on.
Priming is the most important step in making this change successfully. Apply a high-quality stain blocking primer such as Zinsser White Bulls Eye Primer Undercoat Sealer And Stain Blocker. This will lock in the existing colour, prevent tannins or stains from bleeding through your white topcoat, and provide reliable adhesion.
Once the primer has dried according to the manufacturer’s instructions, you can apply your white topcoat. Two coats of a water-based exterior paint, such as Dulux Weathershield or Taubmans All Weather should do the trick.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
