What is Accoya?

[Dave Zellers]

My lumber yard has started carrying Accoya Poplar boards. Ten bucks a LF for 1x8.

I see online that some Accoya products come with a 50 year guarantee. And some siding comes in many "looks".

Anyone familiar with this product and what the process is to make it? It is touted as much friendlier to the planet and highly sustainable. Given that what little I've read so far referred to treating pine, and this is poplar, seems like any softish wood would work. Like maybe cedar.

Anyone used it?

[Greg Quenneville]

Dave, its resin impregnated wood, and yes, they use softer species-must be for greater penetration of the resin? I recall a prototype of that process using a vacuum chamber, but don’t know if that is how it is made in production. **

I bought some here for the bottom rails of my garage doors (the rest is cedar). It was big money, but the fifty year rot resistance sounded good.

**As this thread goes on I realise that I was wrong about the resin…I was thinking of another product. The Accoya cut and machined like normal pine.

[Lee Schierer]

From the Rex Lumber website (https://www.rexlumber.com/lumber/product/accoya/): General Description: Accoya® is 100% solid wood; that is modified to the core using a non-toxic proprietary acetylation process. Accoya® wood is warranted against rot and decay for 50 years above ground, and 25 years in-ground/fresh water contact. The heartwood and sapwood are easily distinguished. The texture is typically fine to medium.

[Dave Zellers]

Well now it makes perfect sense!

"Acetylation is a chemical reaction in which a hydrogen atom is substituted for an acetyl group (CH3C=O group) in a compound. The products formed in acetylation reactions typically have an acetoxy functional group (https://byjus.com/chemistry/functional-groups/). When the hydrogen atom belonging to an alcohol group replaced with an acetyl group in an acetylation reaction, an ester is formed as the product. For such reactions (where the reactant compound contains free hydroxyl groups), the most commonly used acetylating agent is acetic anhydride. An example of an acetylation reaction is illustrated below."

NOT! :confused:

We're a long way from cutting down trees and sawing them into boards. All for the good. This means we'll cut down fewer trees. And with 50 years between residing your house, we can easily grow more trees. Rinse and repeat. Very interesting. One of the products I saw was sidewall shingles. Here in New England this will be huge since we are kind of hung up on the colonial look. 50 years between re-shingling would be well worth the extra cost for many folks. Plus being able to use a wood other than cedar. Sure sounds good to me with what little I know now.

[Dave Zellers]

The quote above is from here-> https://byjus.com/chemistry/acetylation/

Also from that article:

"This process is also known to impart dimensional stability to the wood and increase the hardness of the wood surface. It can be noted that no decreases in the mechanical properties of the wood are caused by the acetylation of wood."

Woah! This could easily find it's way into woodworking outside of rot resistance. 'dimensional stability' :eek:

[Kevin Jenness]

I am somewhat familiar with Accoya, I believe the only species available on the US is plantation grown Radiata pine. It comes very flat and moves very little in service. All the material I have seen is flat sawn and gray streaked, not particularly attractive but can be stained or painted. Accoya has been commercially available in the States for only about 15 years.

[Dave Zellers]

Also from Rex Lumber's web site:

Benefits of Acetylated WoodWhat is Acetylation? https://www.rexlumber.com/wp-content/uploads/2020/10/Acetylation-ENG-1024x572-1.pngRather than spin tales of hydroxyls, hydrogen atoms and other chemistry jargon, in the simplest terms we can muster (in the context of Accoya wood technology) acetylation is: subjecting a softwood to a vinegar, which turns it into a hardwood by preventing the cells in the wood from being able to absorb water.
So acetylated wood is… Pickled wood?
More or less. Yes.
Okay, the chemistry behind this is a little complex, and the vinegar is acetic anhydride. Not quite the malt vinegar for your fish and chips. But the principle is there.
Acetic anhydride? Is that some toxic chemical? Not at all. Don’t let the chemical name scare you. As sodium chloride is actually salt or dihydrogen monoxide is water. Nobody has come up with a sexy name for this vinegar yet. But importantly the reactive organic components are carbon, oxygen and hydrogen. So it’s not toxic at all.
Ok great so acetylation is non-toxic.

[Dave Zellers]

I believe the only species available on the US is plantation grown Radiata pine.

This is partly why I brought it up. This is poplar. They stock 4/4, 6/4 and 8/4.

[Kevin Jenness]

This is partly why I brought it up. This is poplar. They stock 4/4, 6/4 and 8/4.

Sorry, I missed that in your initial post. That is quite interesting since the Accoya website states that they use Radiata pine from New Zealand https://www.accoya.com/faq/what-is-accoya-wood-made-from/ and the Rex website refers to imported softwood. The color and figure of the Accoya I have used could be mistaken for tulip poplar- is it posible that your yard mislabelled it? When I first looked into it I found references to acetylation of other species including hardwoods but couldn't find anyavailable in the US - perhaps they have in fact branched out, so to speak.

[Joe Calhoon]

That is interesting if it is Poplar. All the Accoya I have used or seen Is Radiata Pine. I know they do Thermaly modified wood in Poplar.
The one big disadvantage of Accoya is you have to be careful to use stainless fasteners and where any non stainless metal sits such as a lock box the Accoya should be primed or sealed to prevent the metal from corrosion.
Can you show a picture of the Poplar?

[Jim Becker]

acetylation is: subjecting a softwood to a vinegar, which turns it into a hardwood by preventing the cells in the wood from being able to absorb water.

Softwood remains a softwood and hardwood remains a hardwood as the terms have nothing to do with how physically soft or hard it is. But processing the timber certainly can raise the durability. This is an interesting process, too, for the same reasoning that torification of wood to make it moisture resistance and more durable is. I like that suggestion about pickling...LOL

[Jared Sankovich]

That is interesting if it is Poplar. All the Accoya I have used or seen Is Radiata Pine.

Can you show a picture of the Poplar?

Was just going to reply with the same question about poplar based accoya.

[brent stanley]

I know a number of folks who use Accoya extensively, and have been talking with the UK and North American Accys reps about getting larger dimension versions for Euro sash components.

In North America there was some around for a while that was manufactured here, but the operation was shut down a while ago, and though there may be some of that still kicking around, it was regarded as inferior. As I understand it, the Accoya products that come from the plants in Europe are radiata pine from New Zealand plantations. I know a number of folks who use it, and they say it's fantastic. One guy cut a piece off the end of a 1x8 about 6 years ago and threw it in the ditch at his farm where it has wallowed in excrement ever since. He says other than some staining, it looks that same today. It is incredibly stable and shrinks and swells seasonally less than 99% of woods out there and accepts and holds paints extremely well as a result.

My wife is a chemist and I asked her to look into it. For all intents and purposes you can consider that the process converts some of the compounds in the wood into essentially vinegar. It's not so simple, but that's the gist of it. Since it's all the way through the wood and not a coating, you don't have to worry about treating it at cuts. It's also non-toxic and cut-offs and sawdust don't require any special disposal. At end of life it can be burned safely and if you can get the stuff to compost, it's suitable for use on vegetable gardens!

Many people have managed to stain Accoya and make it look nice, but it's always going to be pine, so cosmetically it won't always work. It's also a bit brittle and can have internal shakes in it that milling will reveal, but in England at least it's warrantied so you can return those pieces and have it replaced. You also need to use stainless fasteners and PU glue with it. It has a 25 year ground contact warranty and there's a side by side experiment from Holland where it was used to line a waterway for 10 years, and the analysis of the products afterwards is very telling.

Though relatively uncommon here, it is heavily used in Europe so there is a lot of user feedback available.

[Dave Zellers]

Excellent info Brent. Re questions posed to me, I haven't seen it, I only came across it when I was checking their inventory of poplar online. Although it is listed on the poplar page, perhaps they just stuck it there for lack of a better place and it is in fact radiata pine. They are only open till noon on Saturday or I'd call. I will ask about it when I'm ready to order my poplar.

All this is certainly interesting, at least to me. Seems like this could replace pressure treated wood in many areas.

[Kevin Jenness]

You also need to use stainless fasteners and PU glue with it.


​Epoxy and resorcinol also work.

[Jeff Bartley]

I’ve worked a bit of it for historic work, specifically sash. The Accoya I get is radiata pine, I’d love to see it in poplar.
This week I get to do a glue up with some, which is a first, I plan to use gorilla glue.
One word of caution: if you have any propensity towards board walk fries or fish and chips make sure you’re well fed before working it….it’ll make your shop smell like a vinegar factory!

[Joe Calhoon]

It’s a interesting material with a lot of possibilities. I’ve made a couple doors with it, as mentioned it’s pine and most of the stock we see in the US has dark stains sometimes that makes it not suitable for stain grade. Rex Lumber has it in all the thickness including 10/4 and 12/4 which is nice for door and window work. I'm just starting a large door and window historical job for an old customer and considered using it. (So much for semiretirement)!. It’s expensive and comparing Genuine South American Mahogany it was a little more and Sipo Mahogany was a little more than half the cost of Accoya. Given the gluing and corrosion issues the Sipo was a easy choice.

For window work with painted exteriors I think a good way to use it is a 3 layer lamination with Accoya outside. This eliminates corrosion issues since no hardware attaches here and a good base to paint on.

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