Outdoor furniture: oil vs varnish

Use a penetrating oil or a wood sealer on outdoor furniture, not a varnish. Oil soaks into the wood and wears away gradually, so you top it up. Varnish forms a film on the surface, and when that film cracks under UV and seasonal movement, water gets underneath it and the only fix is stripping the whole piece back.

The short answer

This is one of the few questions in outdoor furniture care with a clear answer. The failure modes are not equivalent:

• Oil fails gracefully. It thins, the color fades back toward gray, and you clean and reapply. No stripping, no sanding, no point of no return.
• Varnish fails catastrophically. A film that has lost adhesion lifts in sheets, traps moisture against the wood underneath, and cannot be recoated over — applying more varnish onto a failing film just seals the problem in.

Marine spar varnish is the exception that proves the rule. It exists, it is genuinely UV-tolerant, and it survives on boats because owners recoat it on a schedule. A patio chair does not get that attention, which is exactly why varnish is the wrong finish for one.

Why a film fails outdoors

Three forces work on a surface film, and wood outdoors gives all three a lot to work with.

Movement. Wood expands and contracts with moisture. A hard film has to move with it or lose adhesion, and over enough wet-dry cycles the film loses.

UV. Sunlight degrades both the finish and the wood surface immediately beneath it. Once the bond at that interface breaks down, the film lifts even though it still looks intact from above.

Water, once it is in. A breach in a film is worse than no film at all, because the surrounding coating stops the trapped water evaporating. This is the same mechanism that makes a sealed, unvented furniture cover worse than an open one — covered on our page about covers.

Oil, varnish and sealer compared

What to use, by wood

• Teak heartwood: nothing is a legitimate choice, because the decay resistance is in the wood rather than in a finish — the USDA Forest Products Laboratory is clear that heartwood carries a species' resistance. Oil only if you want to keep the honey color. Details on how long teak furniture lasts.
• Acacia and eucalyptus: sealer or oil, every year, not optional. These woods do not have teak's extractives, so the finish is doing real protective work. Our teak vs acacia page is blunt about what happens when the schedule slips.
• Painted or stained softwood: you already have a film, so maintain it as a film — scrape, prime and repaint rather than oiling over it.
• Poly lumber, aluminum, resin and wicker: neither oil nor varnish does anything useful. Plastics and painted metal need a UV protectant, not a wood finish.

The three common mistakes

• Oiling over damp wood. This traps moisture in the surface fibers and can encourage mildew under the finish. Give the wood a full day of drying after cleaning.
• Varnishing to "seal it properly". The instinct is understandable and it creates a future stripping job. Sealer and varnish are different products despite the overlapping language.
• Sanding instead of cleaning. Sanding removes material every time, and a two-part chemical cleaner restores gray wood with far less loss — the sequence is in our restoration guide.

The broader version of this argument is that outdoor furniture cannot be waterproofed at all, only drained: how to waterproof patio furniture works through it material by material.