Replies

1. 
   brucet9 | Jan 18, 2010 05:06pm | #1

   You might contact these folks:

   http://www.forestprod.org/

   Info on the process:

   http://www.forestprod.org/woodprotection06metsa-kortelainen.pdf

   Man, they bake the wood at 350ºF to 450ºF for 2-3 hours!

   Their Power Point presentation says "Not problems with gluing and painting"

   Interesting too, they do not recommend for load bearing applications but good for siding and planking.

2. 
   SgianDubh | Jan 19, 2010 03:36am | #2

   Unless you have specialised equipment available you are unlikely to be able to high heat treat wood to any significant scale or volume. You may be a kiln operator of course and do have the kit required. Here is a selective extract from some text I created following my research on the subject of high heat treatment of wood. You may find it useful. Incidentally, the joinery of high heat treated birch I've used, which is chocolate in colour, was glued up with PVA with no problems. It also polishes up fine with the normal range of polishes. Slainte.

   ************************************************************

   High heat treatment involves heating the wood to temperatures between 150ºC and 250ºC (302- 482ºF) depending on the species and the desired end result. These temperatures are much higher than those that can darken white timbers such as birch and maple as just described. High heat treatments alone would burn the wood so to prevent this steam is introduced into the heating chamber, and the air circulated quickly and uniformly through stickered piles of wood. In all it takes up to four days to treat wood with high heat; up to two days are required to bring the wood up to temperature, between 1/2 an hour and five hours for the treatment itself, and up to twenty four hours are required for cooling. Half an hour to an hour at a raised temperatures 150ºC or just above are used primarily to change wood colour and cause less brittleness—these treatments are used primarily on hardwoods. Higher heat treatment-- ~240ºC for five hours improves external durability of the wood at the expense of a significant increase in brittleness. These latter treatments are mostly used on pine or spruce to increase their durability for use externally.

   Heating wood in this way causes the following effects:

   • It alters the physical and chemical properties of the wood permanently. Degradation of the wood hemicellulose occurs, hydroxyl* groups within the wood decrease. As the wood degrades it produces acetic and formic acids along with phenolic and other aromatic compounds.

   *Hydroxyl. A chemical group in which oxygen and hydrogen are bonded and act as a single entity.

   • The wood darkens— a relatively light heat treatment causes this effect, but the new colour is rather fugitive when exposed to UV light.

   • There is a reduction in changes in the wood’s volume in service with changes in moisture content; this is due to chemical changes in the wood, ie, a decrease in the hydroxyl groups and the effect is to reduce the range of dimensional change, primarily across the grain, as the woods takes on or loses moisture. The volume changes reduce by between 50% and 90% depending on the species compared to normal timber.

   • It reduces the EMC (equilibrium moisture content) of wood through reduced water uptake into the wood’s cellular structure, again, as above, due to smaller amounts of the wood’s hydroxyl groups. This affects the take up of moisture in water based glues thus requiring longer clamping up time when joints are assembled.

   • It makes the wood more brittle, and the higher the temperatures used the more brittle it becomes. This may make the wood less desirable where strength is critical, eg, when used for building materials in the construction industry. More brittle wood also requires sharper cutting tools to work it effectively, and the dust produced is finer than normal and is therefore more likely to be a respiratory irritant.

   • Improved durability of wood (for use externally) due to chemical degradation of the wood’s components. Significant improvement in decay resistance occurs when the wood is subjected to temperatures above 220ºC (428ºF), although the treated wood is not durable if it is used in ground contact situations.

   • 5-15% weight loss which may have an impact on transport costs and the weight of structures built with the material. Reduction in transport costs, and therefore fuel savings, would have to be weighed against the cost and environmental impact of the high heat treatment.

   • Annual rings visible on wide faces of the wood may delaminate, particularly if they show as an arching pattern due to tangential milling and intersect the face at a low angle. For this reason the preferred cut is rift sawn planks where the annual growth rings intersect the faces at between 30º and 60º with 45º being ideal.

   • The resin of pines exudes out of the wood which means the equipment used to effect the treatment requires frequent cleaning, but the reduced resin content of the wood is an advantage in situations where resin free wood is desirable, eg, garden furniture such as chairs, benches and tables.

   • Knots, particularly in pine, may loosen, crack, or cause distortion in the surrounding wood.

   • Birch species are liable to warp significantly during the treatment which may make the treated boards unsellable.

   Lightly treated birch finds uses as flooring, cladding and furniture; heavily treated pine and spruce become more durable and are used externally for building construction and other external structures; aspen finds uses for indoor sauna construction and other high relative humidity situations.

1. 
   MWF | Jan 21, 2010 08:35am | #3

   The reason I asked the question is I am doing a project with thermally treated wood and needed help on my glue choice. I am building a nest to hold a high end grill/smoker and need to use a green product. The wood is treated localy and I am very familiar with the process, but information is limited on glue choice. The wood does require oil based finish if a finish is desired.

   Thanks

   MWF

2. 
   zgmc | Jan 25, 2010 08:50am | #4

   SD: Thanks for posting, very informative.