Wood
How often does exterior wood need maintenance?
Sun, rain and the position of the surface set the schedule. Learn the signs and give the right care at the right time.
Short answer
There is no single interval: sun, rain, the direction the surface faces and the coating system decide it. Horizontal surfaces exposed to sun and rain, such as decks and terraces, usually need care every year or two. On vertical and sheltered surfaces semi-transparent systems last several years. Regular inspection is the most reliable guide.
1What sets the maintenance interval?
- Sun: UV radiation breaks down the lignin at the wood surface and ages the coating. Surfaces facing south and west wear faster.
- Water: Rain, snow and dew make the wood swell and shrink, which cracks and blisters the coating.
- Position: On horizontal surfaces water and sun act for longer, and people walk on them. Vertical surfaces and wood under the eaves last much longer.
- Type of finish: Oils and thin wood stains are easy to renew but need care more often; film-forming opaque systems last longer but are harder to prepare once they fail.
- Pigment: Well-pigmented shades protect better against UV; clear varnish is the shortest-lived option outdoors.
2A typical schedule by system
| System | Horizontal (decking, terraces) | Vertical (cladding, joinery) |
|---|---|---|
| Wood oil | Usually every year | Every 1-2 years |
| Semi-transparent stain | Every 1-3 years | Every 3-5 years |
| Opaque system | Usually not recommended | At longer intervals than other systems |
| Clear varnish | Not recommended | Short-lived, needs frequent renewal |
These intervals are a guide. On the same house, a south-facing window frame and a door under the eaves can differ by several years; the maintenance advice in the product’s data sheet takes precedence.
3Signs that maintenance is due
- Faded, grey or dull surfaces
- Water soaking into the wood instead of beading on the surface
- Fine cracks, blistering or flaking in the coating
- Darkening, mould or algae at end grain and joints
A simple test: pour a little water on the surface. If it beads, the protection is still working; if it soaks in within a few minutes, maintenance is due.
4How to do the maintenance
- Clean
Remove dirt, algae and loose material with a brush and a suitable cleaner. Use a pressure washer with care; it can raise the wood fibres.
- Let it dry
The wood must be completely dry. A coating applied to damp wood does not hold; most exterior systems are applied when the wood moisture is below roughly 15-18%.
- Sand
Lightly sand grey or degraded wood until you reach sound timber, then remove the dust.
- Renew with the same system
Apply a product compatible with the existing coating, in the recommended number of coats. Seal the end grain and joints first.
5Measures that extend the life
- Treat new timber with impregnation and primer on all faces before installation.
- Seal end grain and screw holes separately; that is where most water gets in.
- Leave falls and gaps on horizontal surfaces so water does not stand.
- Choose pigmented systems over clear varnish; the pigment adds UV protection.
- Repair small damage straight away; it is easier than renewing the whole surface.
Browse the product groups on our Wood Coatings page for exterior systems, or ask our technical team about your project. For the differences between furniture lacquers, see our water-based vs solvent-based guide.
Frequently asked questions
How often should decking be oiled?
On decks exposed to sun and rain, oil is usually renewed once a year. The water test shows whether it is time.
Can clear varnish be used outdoors?
It is not recommended. Clear varnish gives limited UV protection, cracks and peels in the sun and is hard to renew. Pigmented stains or opaque systems last longer.
Can grey, weathered wood be saved?
Often, yes. The grey layer comes off with cleaning and sanding; once sound wood shows, the surface is protected again.
Which season suits maintenance?
Choose a dry, mild period without rain. Applying in very hot, direct sun can make the coating dry too fast and leave marks.