Accoya

[Livingston Johnston]

Hey Folks,

Lately i have been fielding a lot of requests for Accoya windows and doors. Does anyone have experience with it? My lumber salesman offers a 50 year warranty against rot and raves about how stable it is. My exterior doors are generally 3 layers of 3/4" face laminated to make 2.25". Again, my saleman states i can just use 10/4" accoya and avoid glue up as the lumber wont warp. Is this stuff really that good or is it too good to be true

[peter gagliardi]

I'm thinking we won't know for another 50-75 years.
In the meantime, I will let others conduct the experiment.
The salesmen really pushed Lyptus for a few years too, you don't hear anything about it any more.

[David Munyak]

I've used it once, just recently. A client with two garage doors that were in fine condition except for the bottom panel on one door which had sustained some damage years ago, resulting in a rotted bottom rail.

I reproduced the whole bottom panel, which was a frame and panel arrangement with four raised panels. I used Accoya for the frame and Medite for the panels.

its only been in for a month so who knows how long it will last, but I hope it will outlast me.

The Accoya was fairly easy to work with. Did not seem to be a lot of tension in the wood when ripping on the table saw. Once ripped, it seemed stable and didn't bow or twist much.

The dust that's produced when sawing or routing is quite fine. It machines smoothly but it does seem to be a bit brittle so sharp corners and edges can chip or be pulled up if not machined carefully.

Since this his was going to be in an exposed location, I chose to use epoxy for assembly and pre-primed exposed end grain with the epoxy. The end grain absorbed a fair amount of epoxy.

It took paint well.

I like the fact that it's made from a fast growing, renewable resource, but I do hope they've got the process worked out to make it rot resistant. It would be nice not to have to use mahogany or Spanish cedar for paint grade work.

since I have some scrap left, I plan to use some for garden stakes to see what happens over time. I may do some moisture absorbency tests as well. All in my spare time, of course.

Hope this helps a little.

[Joe Calhoon]

We have built a few doors out of Accoya all in bad exposure situations. They have only been out for 2 or 3 years now so too soon to tell anything. I would say it holds more promise than thermally modified wood or Red Grandis. It’s as expensive as Sipo or Sapele. I think the Radiata Pine comes from South America and the treatment done in Europe so high mileage by the time it gets here. Maybe it’s produced here now, I don’t know.


The Accoya we used had dark streaks running through that made it unsuitable for any stain grade. We sat through an Accoya presentation in a German shop that was using it and asked the Accoya rep about this as all the Accoya I have seen in Europe is very clear and color consistent. Showed him the pictures and he was baffled about that. Some other US shops have seen the same thing.


The small amount we used seemed pretty stable but noticed when ripping out glass beads a couple of those went spaghetti. The wood machines easy enough. I worry about the toxic effect the dust may have long term even though they say it is ok. On the plus side low wood movement should translate to longer lasting exterior finishes. You need to use stainless fasteners on all the hardware.


It is widely used in UK door and window shops in solid form and Mainland Europe shops are using a lot on the outer layer of 3 layer scantlings. This would avoid the corrosive issue.


The jury is still out for me but I do think it holds promise as the supply of good door and window wood is on the decline.

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[Kevin Jenness]

The shop I last worked for has gone all in on accoya for exterior painted work. Time will tell how good that choice is. The process has been around since the 1930's. The idea is that free hydroxyl molecules are replaced with acetyl groups that do not take up moisture as easily. It is very stable, comes flat and stays that way when ripped. It is very thirsty for glue, so be careful when using epoxy to prime end grain repeatedly and use an additive like cellulose flour to ensure resin in the joints. The manufacturer claims to use other species, but as far as I know only radiata pine is available in this country. The stuff I have seen is the ugly gray shown in Joe's photos. It has a whiff of vinegar resulting from the acetic acid used in the treatment, and is rather corrosive to metal. Here is a link to a ground contact study comparing accoya to teak, western red cedar,, macrocarpa and cca treated radiata pine. https://www.accsysplc.com/wp-content...05/scion-6.pdf.

David, what flavor of Medite did you use? Most grades are not recommended for exterior use, although I was interested to learn that there is a Medite Tricoya board that has the same chemical treatment as accoya lumber.

[Erik Loza]

Yep, Accoya is that good. It was one of two modified woods that were used in our primary business channel of exterior siding (when I was with Delta Millworks). Routinely did 10K+ SF jobs of T&G exterior cladding with it is the most dimensionally stable of any of the modified woods out there. Any climate and high-moisture, no problem. One note: It is fussy about the stains and finishes it likes since the acetylation process closes the cell walls. Finishes must be penetrating oil-based and even when stained, Accoya has a "funny" look to it. Like birch ply, but solid stock of course. In fact, the biggest objection I got from architects was the look. As far as dimenisonal stability though, it is awesome stuff. Hope this helps.

Erik

[Kevin Jenness]

After doing a little more reading I realized that my "thirsty for glue" comment is not the whole story. The end grain is definitely that way, and thorough end sealing is recommended to prevent wicking of moisture. What moisture is taken up is primarily "free" water, in and between the cells, as opposed to "bound" water that bulks up the cell walls and causes dimensional changes and warping. Because of the resistance to cellular absorption, it takes longer for long grain surfaces to accept glue and the recommendation is to wet out both surfaces and allow for longer open and closed time before clamping to avoid starved joints.

[David Munyak]

David, what flavor of Medite did you use? Most grades are not recommended for exterior use, although I was interested to learn that there is a Medite Tricoya board that has the same chemical treatment as accoya lumber.

Kevin,
I'm not sure exactly. It seemed elusive in my area. Found a local yard that ordered it for me but said they had sold it to signmakers in the past who had no problem with it. I'd initially considered Extira but that was harder to find and I'd read that it has an oily surface that I worried would affect the paint bond. After I milled the raised panels, I coated the cut areas with epoxy prior to assembly as extra insurance against moisture absorption.