[Greenbuilding] heat treated wood siding

[John Salmen]

There was some discussion of this 'torrefaction' as a wood preservative
treatment - there were some french companies involved at the time. Flame
treating or charring and burnishing of wood surface was a traditional
Japanese exterior wood technique and I have done that on a few projects (yes
architecty/finicky) but can be done with some modern tooling and the results
are stunning. The traditional approach was burning the surface of the wood
with brazier heated irons and then laboriously burnishing the char off the
wood. The heating would affect the top 1/4" or so of the wood (similar to
torrefied) and the burnishing would polish off the sacrificial carbon
('staining') components and leave the wood with a burnished grey appearance
that are quite stable both in colour and texture. In reproducing this we
used large torches and metal and synthetic burnishing (texturing) wheels.
There are acid treatments (life time/ valhalla) that leave a similar
appearance. 

Depending where you live the 'elements' will typically take close to a
century to erode a 1/4" off the surface of raw untreated wood so typically
wood doesn't need treatment if it has enough sacrificial depth. If the wood
is finished it is the finishes that need renewal - and often the finishes
trap moisture (more typical of older oil finishes - less a concern with
breathable). 

What the burning or acid treatments do is give a natural and neutral aged
grey finish to wood buildings that otherwise would take quite a while to
achieve that. After all it took me over 50 years to get that appearance.



-----Original Message---
From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org]
On Behalf Of John Straube
Sent: November-12-15 5:17 PM
To: Green Building
Subject: Re: [Greenbuilding] heat treated wood siding

I am assuming Sacie you mean heat treated for cladding, not kiln dried or
heat treated to kill bugs for shipping pallets For those who dont know about
this process google "heat treated wood cladding" and you can read about it.
It involves heating to 180-200 C/350-400F or so.  It causes a reduction in
ductility, but apparently significantly enhances durability.  
One technique that is a bit less controlled is to flame treat the wood and
char it. Some people like the look (e.g. architects) but it is a finicky
process and often run off from rain results in significant staining.
The controlled Scandinavian process of heat treating results in some
excellent durable products, especially if it is painted right after (as a
lot of this product apparently is). The common method is to heat in an inert
gas atmosphere, but I have heard that hot oil is also used and has
advantages It seems that it is quite durable, a natural pressure treatment. 

On Nov 12, 2015, at 4:56 PM, Sacie Lambertson <sacie.lambertson at gmail.com>
wrote:

> I am interested in this group's opinion about using heat treated wood on
the exterior of a house in NE Kansas?
> 
> Thanks, Sacie
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John F Straube
jfstraube at uwaterloo.ca
www.JohnStraube.com




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