How to paint hardwood timber that has been oiled?

[AnneM1]

I have doors and privacy screens made of hardwood and have  oiled them with decking oil on a regular basis and now I want to update the outside of our home and would like to paint the timbers.  What do I need to do to prepare the timber?

[MitchellMc]

Welcome to the Bunnings Workshop community @AnneM1. It's amazing to have you join us and many thanks for your question about painting oiled timber.

To prepare hardwood timbers that have been oiled for painting, the approach depends on the type of oil previously used. If it were a water-based decking oil, start by giving the timber a light sand to remove surface build-up, then apply Dulux 1-Step Primer. Once the primer is fully dry, follow with two topcoats of Dulux Aquanamel for a durable finish.

If the timber has been treated with an oil-based decking oil, you’ll need to first use Cabot’s New Timber Prep to strip out the oils, then follow with Cabot’s Deck Cleaner to remove any remaining residues from the surface. After this preparation, apply a Dulux oil-based undercoat, allow it to dry completely, and finish with two topcoats of Dulux Aquanamel. This process ensures proper adhesion and a long-lasting painted finish.

Please let me know if you have any questions.

Mitchell

[AnneM1]

Hello MitchellMc thanks for our advice, but we can't use this method as the timber is slats on the side of decks and we have gardens underneath and my research shows me that this stuff is pretty toxic.   We thought we might try to sand it and then use an oil based primer and then we should be able to paint it with a waterbased top coat.  What do yo think?  Anne

[MitchellMc]

That could possibly work, @AnneM1. However, sanding doesn’t actually draw out the oils that are already within the timber. Even after sanding, if the timber has been regularly oiled, you might just expose more timber that’s equally saturated with oil underneath.

If you were able to sand right through to completely unoiled timber, that would definitely be the ideal approach. But if a penetrating oil has been used, it can soak several millimetres deep into the surface, so there’s no guarantee sanding alone will remove it all.

Since stripping isn’t an option in your case, your best approach would be to give it as thorough a sand as possible, then use an oil-based primer followed by your water-based topcoat. Just keep in mind adhesion might still be a bit of a challenge depending on how much oil remains in the timber.

Mitchell

[AnneM1]

What if we painted with an oil based paint both primer and top coat?  Still sanding first.  

[MitchellMc]

If the timber is saturated with oil, @AnneM1, applying an oil-based primer or topcoat won’t solve the problem. While an oil-based topcoat can help prevent tannin or stain bleed-through, it won’t improve adhesion if the primer can’t properly bond to the surface. The key issue is that oil on or within the timber prevents primers from penetrating and forming a mechanical bond. Even oil-based primers require clean, dry, and bare timber to adhere effectively.

In this case, surface preparation is far more important than the coating type. The timber needs to be thoroughly cleaned and de-oiled, often through sanding, washing with a suitable solvent or cleaner, and allowing ample drying time before any primer is applied. Otherwise, no matter what coating is used, the adhesion will be compromised.

Mitchell