Timber Treatment Calculator — Preservative & Oil Quantities

Decking should be oiled every 12-18 months. Fences should be treated every 2-3 years with preservative or fence paint. Exterior joinery (windows, doors) needs varnish or stain refreshing every 2-3 years depending on exposure. South-facing surfaces may need more frequent treatment.

Most timber treatments need 2 coats for adequate protection. Bare, untreated wood should have a preservative base coat followed by 2 coats of stain, oil, or paint. Previously treated timber that is still in good condition may only need 1 refresher coat.

Coverage varies by product: Wood preservative covers about 6 m²/L, decking oil 8 m²/L, fence paint 8 m²/L, exterior stain 12 m²/L, and exterior varnish 14 m²/L. Rough-sawn timber absorbs more than planed timber, reducing coverage by up to 30%.

Yes, but wait at least 6 months for new pressure-treated timber to dry out before applying oil, stain, or paint. The treatment chemicals need time to fix in the wood. You can apply water-based treatments sooner (after 2-3 months) than oil-based ones.