Teak and oily wood outdoor care

Overview

Teak, and to varying degrees other oily or dense tropical woods, shed water and resist adhesion. The Wood Handbook says a naturally water-repellent surface is expected for oily woods such as teak, and that if water beads, finishes are likely to have trouble sticking; the usual cause is a surface contaminant, and a few passes with sandpaper are often enough to remove it. You then have three paths: leave it to weather to silver-grey, oil it, or build a varnish. Each is a maintenance decision, not a one-off.

When to use

Garden and boat teak, and oily outdoor species such as Ipe and Iroko. Not needed for naturally durable wood you are happy to see weather; the Wood Handbook describes weathered wood as silvery grey because weathering removes coloured components from the surface.

Materials and tools

• Acetone or another degreasing solvent. Epifanes, a marine coatings maker, says to degrease oily, resinous woods such as teak with acetone, and does so repeatedly.
• Oxygen-bleach (sodium percarbonate) cleaner for dirt and mildew; the Wood Handbook says it is less likely than chlorine bleach to damage wood, and FinishLine 013 cautions against combining bleach with ammonia.
• Fine abrasive. Avoid steel wool and wire brushes on tannin-rich woods: iron particles stain them (FinishLine 006 on iron stain).
• A penetrating oil or varnish (see Steps).

Steps

1. Clean. Scrub with oxygen-bleach solution and a soft brush, rinse and let dry fully.
2. Degrease immediately before finishing. Wipe the surface with acetone on clean rags, changing rags often, several times (Epifanes). Avoid touching the surface afterwards with bare hands, which re-contaminate it (my practical advice, not from a source).
3. Sand lightly to remove surface contamination (Wood Handbook). Sand at 120 to 180 grit (Sanding schedule).
4. Pick one finish.
   • Teak oil. A maker's label describes teak oil as formulated for dense woods such as teak and as protecting from moisture and UV; Watco is one such label. See Teak oil for what is actually in these products. Expect to renew them often.
   • Penetrating sealer plus film. See Outdoor finishing.
   • Marine varnish. Epifanes describes thinned first coats (50%, 25%, 15%) then 5 to 6 build coats, with more coats in strong UV. Moisture content should be at most 17% before varnishing. Their guidance sits behind Marine and boat finishing.
   • Bare. Clean annually with oxygen bleach.
5. Avoid a surface that stays oily. The Wood Handbook warns that if too much penetrating stain is applied the wood may stay oily for a few weeks; wipe excess.
6. Re-apply when water stops beading or the colour fades, not on a fixed date.

Common problems

• Finish peels off or never dries. Surface oils not removed: degrease and sand, then recoat.
• Dark stains from steel wool or iron. Iron reacts with tannins in the wood (FinishLine 006); avoid steel wool and iron contact.
• Grey weathering you dislike. The grey is surface weathering only; clean and oil, or sand lightly.
• Mildew on oiled teak. The FPL says natural oils feed mildew; clean with oxygen bleach and re-oil only after it is dry.
• Epoxy on teak. Follow the epoxy maker's surface-preparation instructions; see Marine and boat finishing.

Safety and environment

Acetone is highly flammable: no ignition sources, ventilate, and keep wet rags in a covered metal container and away from the building (Finishing shop ventilation and PPE). Oil-soaked rags can self-heat: Oily rag safety. Wear a dust mask and gloves when sanding any tropical hardwood; I did not find a source for species-specific dust hazards in teak.

Related

• Teak oil, Degreasing oily woods, Spar varnish
• Outdoor finishing, Marine and boat finishing
• Teak, Ipe, Iroko
• Cleaning and care of finished furniture, Long-term finish ageing and patina