can you use the shou sugi ban charring technique on green lumber?

hello, permies.

i'm new to this space and am grateful for all the incredible knowledge and insight. coming in with some questions of my own ...

i am currently milling up .5" cedar and hemlock planks to use as board + batten siding for a new pump house for our well. the trees were felled in june of 2023 and i'm aiming to use them in the build this spring/summer (2024). planks are currently stickered up and drying under a large carport but they will not be fully dried by the time we're ready to start building with them.

we are wanting to use shou sugi ban to help preserve the material and create a pretty little pump house. i'm wondering whether or not it is advisable to use this technique on wood that hasn't been fully seasoned. does anyone know?

likewise, if the wood is still green, i assume that the moisture content will make it less capable of absorbing a treatment mixture, is that correct? i'm currently thinking of using tung oil, mineral spirits, and paraffin wax but if there's a more advisable concoction for using green lumber in exterior applications in the PNW, please let me know!

thanks in advance for any insights and best of luck on your own projects!

graham

Welcome to permies, Graham. I've wondered about this as well, and haven't seen any recommendations for or against. Intuitively, I'd think that charring green softwood would be a great way to go, because the moisture in the interior of the boards will prevent some of the structural weakening that comes with torrefaction. Of course, if you're using it for cladding then it doesn't really need to be all that strong, and you might have more shrinkage to contend with...but that's the whole point of board and batten, to accommodate expansion and contraction and still have a weathertight skin.

I'd be keen to know how it performs if you do go down this path.

On a tangent to this, I'm trying wood vinegar as a preservative on some untreated pine that I'm using to make gates (recycled pallets, not heat treated even). The boards were really dry from being outdoors in the late summer, so when I brushed it on it penetrated well. I don't think you'd have good results putting any type of liquid finish on green timber, but daisugi may be an exception.

I think the technique of charring is a bigger factor than using green or damp wood. If you do the "tie three boards together to make a chimney and have the fire go up the inside" method, the draft will be absolutely ripping and you can char some pretty wet wood. But if you try to char individual boards using a propane torch, it's gonna take forever regardless of whether it's wet or dry.

I did my whole house using the chimney method with salvaged boards that got rained and snowed on, and I didn't put any kind of finish or preservative on it. Holding up fine 8 years later but I'm in a pretty dry place where rot isn't so much an issue like the PNW.

Cedar's pretty rot resistant, so maybe don't even go to the trouble of using any wood preservative on those boards.

Hi Graham,
We’ve tried it all here at Northwest Shou Sugi Ban.

Green wood can be charred, as you suspect, but I would avoid it for the durability and longevity that you might want.

We did a small cabin using the inexpensive green cedar fencing boards (like you used to be able to get at Home Depot for $2). While the finish looked pretty good, I don’t feel like we were able to get a true deep char, heating the timbers through with enough intensity, due to the steam that the moisture creates.

I don’t think you can count on the flash heating of the charring process to also be able kiln dry your timbers. We only use properly kiln dried after that experiment.

That’s my 2 cents,

Steve Keyser
www.northwestshousugiban.com

Hi Steve, thanks for the knowledgeable insight. Someone built a house locally and used charring for the exterior finish (I'm not sure what the wood was, but not very local) It does look nice!