Accoya

Accoya

Accoya is the most durable and most stable timber we stock, and it started life as a softwood. Radiata pine (Pinus radiata) is acetylated, a chemical modification that changes the structure of the wood itself rather than coating it, and the result is durability class 1: better in ground contact than most tropical hardwoods, from a fast growing plantation species. If you are specifying windows, external doors, cladding or bridge decking and you want the job to outlast you, this is the timber that does it. Grown in New Zealand, acetylated in the Netherlands, stocked in our yard for delivery across Ireland in thicknesses from 26 to 100 mm, with FSC certified supply available on request. Sold by the cubic foot and priced on enquiry.

Why Accoya?

Durability is only half the story. The reason joiners keep coming back to it is stability. Acetylation reduces dimensional movement by roughly three quarters, so an Accoya window stays square through an Irish winter in a way ordinary timber simply does not, and a wide external door stops binding in wet weather. That stability is also why coatings last so much longer on it: paint fails when the substrate underneath moves, and this one barely does.

It also machines beautifully. It is soft enough to work easily, holds a crisp profile, glues reliably and takes a finish evenly. For a workshop used to fighting oak, it is a pleasure.

The honest points are two. It is expensive, and there is no way around that: you are paying tropical hardwood money for modified pine, and the case for it rests entirely on service life rather than on purchase price. And freshly machined Accoya carries a faint vinegar smell from the acetic acid used in the process. It is harmless and it fades within days of the timber being in open air, but it surprises people the first time they open a pack.

Installation guidance

If you have worked softwood joinery, nothing here will catch you out, with one exception that matters a great deal.

The residual acetic acid corrodes ordinary metal. Use A4 grade 316 stainless steel for every fixing, fitting, hinge and bracket that touches the timber. Galvanised is not sufficient and mild steel will fail. The same applies to anything Accoya sits against, so avoid direct contact with unprotected aluminium or mild steel in a wet detail. Beyond that, pre drill near ends and edges as usual, and seal cut ends and drilled holes to keep the coating system continuous.

Finishing & maintenance

Two routes, and Accoya makes both easier than usual. Leave it bare and it weathers to a soft silver grey over roughly twelve months, losing nothing in durability because the protection is in the timber rather than on it. Or coat it, and here is where Accoya earns its money: coatings on a substrate this stable last far longer between recoats than the same system on unmodified timber. Most of our customers coat windows and doors, where the appearance matters, and let cladding silver.

If you are coating, use a flexible microporous system rather than a hard film forming gloss or yacht varnish, which will still crack at joints. We stock finishes suited to modified timber, so ask us which to pair with yours. For both routes, a wash with warm soapy water and a soft brush is the only regular cleaning it needs.