How do I treat fences, decking and outdoor wood?
Preparation, choosing between stain, oil and paint, and the timing that determines whether it lasts.
- Difficulty
- beginner
- Time
- 4 hr
- Read
- 2 min
Short answer
Clean and dry the timber thoroughly first, and apply on a dry day with no rain forecast for 48 hours. Most outdoor timber treatments fail because they were applied to damp or dirty wood.
Outdoor timber treatments protect against water and UV. They fail almost entirely on preparation — applied over dirt, algae or damp, they cannot penetrate and they peel or wash off within a season.
What you'll need
- Stiff brush
- Treatment
- Brush or sprayer
- Pressure washer (optional)
- Dust sheets (optional)
Step by step
- Choose a dry spell.Dry timber, dry day, and no rain forecast for 48 hours. Applying to damp wood or before rain is the main reason treatments fail.
- Clean thoroughly first.Brush off dirt, algae and loose material. A cleaner or pressure washer for heavily soiled timber — but then allow several days to dry out.
- Let pressure-washed timber dry completely.Several dry days. Washing drives water deep into the timber and applying treatment over it traps the moisture, which causes rot.
- Sand or scrape any flaking previous coating.New treatment over failing old treatment fails with it. Remove anything loose back to sound material.
- Choose the product for the timber and the look.Penetrating oils and stains soak in and weather gradually. Paints and opaque coatings sit on top, look solid and eventually peel.
- Treat the end grain generously.Cut ends absorb far more water than faces. Extra treatment on end grain, particularly at post bases and rail ends, is where the timber fails first.
- Apply thin even coats, working with the grain.Two thin coats penetrate better and last longer than one thick one, which sits on the surface and peels.
- Reapply on schedule.Every two to three years for most treatments, more often on south-facing and exposed surfaces. Reapplying before it fails is far easier than stripping and starting again.
Tips
- Treat the underside and back of fence panels and decking boards if you can reach them. Water gets in there and it is never treated.
- A sprayer is far faster than a brush for a long fence, but brush it in afterwards so it penetrates rather than sitting on the surface.
- Decking gets slippery with algae. A dedicated decking cleaner once a year is a safety measure as much as a cosmetic one.
Common mistakes
- Applying treatment to damp timber — It cannot penetrate and it traps moisture inside the wood, which accelerates rot rather than preventing it.
- Pressure washing and treating the same day — The timber is saturated. It needs several dry days before anything is applied.
- Ignoring end grain — Cut ends absorb many times more water than faces. Untreated end grain at post bases and rail ends is where outdoor timber fails first.
Questions people ask
When should I treat a fence?
On a dry day after several dry days, with no rain forecast for 48 hours. The timber must be dry throughout, not just on the surface.
How often does outdoor timber need treating?
Every two to three years for most products, and more often on south-facing or exposed surfaces. Reapplying before the coating fails is far easier than stripping it.