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Pressure-treated wood care: cleaning, staining, oiling

The Wood Guide · Care & finishing

Care by wood species · pressure-treated spruce

Caring for pressure-treated wood

The wood of our picnic tables and garden benches — and one of the most misunderstood kinds of wood. What pressure treatment does and does not do, and so what you still need to do yourself — less than you think.

  • Protected against rot and fungi
  • Not waterproof
  • Adding colour is fine, once it has dried
green → honey → grey
Summary

The protection is inside the wood — so you don't have to maintain it

With paint or stain, the protection sits on the outside and wears away. With pressure treatment it doesn't. That is the whole difference.

In pressure treatment, the wood goes into a vessel from which the air is first extracted. A preservative is then forced deep into the fibres under pressure. The result is spruce that stands outdoors for years without rotting from within.

Because the protection goes deeper than any layer you would ever sand away, no annual treatment is needed to make the wood last. What you do do: clean it, retighten the bolts, and — if you like — give it a colour.

What pressure treatment does not do

It does not make the wood waterproof: it keeps absorbing and releasing moisture, and so it moves. It does not prevent small cracks. And it does not hold the colour: pressure-treated wood turns grey too. Once you know that, nothing will alarm you. See also cracking and warping.

Protects against
wood rot · wood-destroying fungi
Does not protect against
moisture · small cracks · greying
Required maintenance
none · cleaning is enough
Adding colour
wood oil · after a few weeks of drying
Service life
usually 10 to 15 years
Outdoors
all year round

To be fair: pressure-treated spruce is not as durable as teak or tropical hardwood, and it remains a soft wood that can get dented. What it wins on is light weight, a fair price and a long life for what it costs.

Background

What pressure treatment does to the wood

Deep in the fibre

The preservative is introduced under pressure, not painted on. That is why you can sand pressure-treated wood and give it a colour without removing the protection. The full process: pressure-treating wood.

Why spruce

Spruce grows straight, fast and close to home, and it is easy to work. By nature it is vulnerable outdoors; pressure treatment changes that. More about the species: what is spruce.

The difference from lacquered wood

Beer tables and beer benches are not pressure-treated but lacquered. That gives a smooth, stain-resistant surface, but they should be stored somewhere dry after use. Choosing beer tables.

The difference from Douglas fir

Douglas fir is naturally more durable than spruce and needs no pressure treatment to stand outdoors. Part of our Douglas fir is colourlessly pressure-treated. What is Douglas fir.

Colour change

From green to honey to grey

  1. On delivery: a greenish tingeNot paint, but a remnant of the treatment process. Each board takes up the preservative slightly differently, so one board is greener than another.
  2. After a few months: honey colourSun and rain fade the green tinge to a warm, light honey shade. Colour differences between boards even out.
  3. After one or two seasons: greyLike any wood that stands outdoors, it turns silver grey. That is weathering of the surface, not decay.
Green tinge or green algae?

Two different things. The green tinge of new wood is in the wood and disappears by itself. Green algae grow on the wood, mainly in shady, damp spots; you brush them off with lukewarm water and soft soap.

The only regular job

Cleaning

Do

Lukewarm water, a soft brush and a little soft soap, in the direction of the grain. Rinse well and let it dry. Once or twice a year is enough.

Don't

No pressure washer: spruce is soft at the surface, and the jet washes away the fibres between the growth rings. That damage is permanent. No bleach or ammonia.

Resin spots

Spruce can release some resin in its first warm summer. Let it harden, scrape it off flat and remove the rest with white spirit.

Retighten the bolts

A month after delivery and then every spring. The most important maintenance there is.

Adding colour

Staining or oiling pressure-treated wood

You can add colour, and it doesn't remove the protection. The most important thing is patience.

  1. Wait until the wood is dryFreshly treated wood does not take up oil or stain in the first weeks. Let it acclimatise outdoors for a few weeks to a couple of months.
  2. Clean and let it dryNothing adheres well to dirty wood.
  3. Sand lightlyFine grit, with the grain.
  4. Apply thinlyWith a brush or lint-free cloth. Two thin coats give a nicer result than one thick one. Don't forget the end grain.
  5. Dry weather, above 10 degreesAnd not in full sun.
Tinted oil, not gloss paint

Tinted wood oil soaks into the wood instead of forming a film on it, so it cannot flake. Touching up later is simply a matter of applying it again. A closed gloss paint traps moisture and starts to flake after a few seasons. The difference between stain and oil: stain or wood oil? All maintenance by season: caring for wooden garden furniture.

Quick answer

Frequently asked questions about pressure-treated wood

Do you need to treat pressure-treated wood?

No. The preservative has been forced deep into the fibre under pressure and protects against wood rot and fungi. Cleaning is enough. You only stain or oil for the colour.

When can you stain or oil pressure-treated wood?

Only once the wood is dry. Freshly treated wood does not take up oil or stain in the first weeks. Let it acclimatise outdoors for a few weeks to a couple of months, clean it, let it dry and sand lightly.

Does the green colour of pressure-treated wood go away?

Yes. The greenish tinge is a remnant of the treatment process, not paint. In the first months outdoors it fades to a warm honey colour and then to grey.

Is pressure-treated wood waterproof?

No. Pressure treatment protects against rot and fungi, but the wood keeps absorbing and releasing moisture. That is why it still moves and fine cracks can appear, just as with untreated wood.

How long does pressure-treated wood last?

A pressure-treated picnic table or garden bench with thick boards usually lasts 10 to 15 years, and longer if the legs don't stand in water and you retighten the bolts regularly.

More in The Wood Guide

From knowledge to garden

Pressure-treated spruce is the wood of our picnic tables. Now you know what it needs.

KING picnic tables Restol wood oil To The Wood Guide

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