Thermowood and Sawn wood
Overview:
Fire can make the wood durable. Also Vikings hat this experienced for outdoor fences which is with fired strengthen.
ThermoWood is manufactured using a method that sawn timber is heated up to 180 degrees Celsius and at the same time steam protected the wood for burning. Also the steam affect the chemical changes in sawn timber. ThermoWood is darker, more stable than normal sawn timber.
Type and quality:
According to thermoWood Handbook:
“we have two type of thermo wood:
1- Thermo Wood S:”S” means stability.The average moisture of ThemoWood class is 6-8%
2-Thermo Wood D:”D” means durability. The average moisture of ThemoWood class is 5-6%
ThermoWood S is not suitable for exterior decking, cladding and furniture and only ThermoWood D is suitable in this respect.
For Thermowood production we have different type of sawn timber and it is controlled with a quality grading system according to the number,quality location and size of the knots :A ,B and C and A is subdivided to A1,A2,A3 and A4.
Minimum requirement of sawn timber for pine: the number of sound/dead knots on the worst 2 meter of sawn timber length on face is 8/2 and on edge is 4/1 .knots with bark or hole are not permitted.”
Installation and selection:
It is important that the sawn timber are from the center of the wood. This center for cladding and installation of thermo Wood use as a surface side. The knots from outside the sawn timber into inside the sawn timber get wider and converted into special shape like a wind or butterfly and can give a beautiful view to the facades. Furthermore the quality of knots get better with less hole, which cause less water penetration and as a result higher durability.
One of the problem of sawn timber with many age rings is that the thermo wood is weaker in these rings and started to cracking through these places especially in decking. In deking the thermowood exposed to more rain, sun and weather conditions and these wetting and drying cause more curving and striating in thermo sawn wood and a result start to cracking from the aging rings. So Applying 2 screws in decking is suggestible for preventing these cracking as it can prevent curving and striating.
Another obstacle in thermo wood installation is the high bending of sawn timber.
Only screws in clos distance can prevent its bending. Nails cannot the strength of wood tolerate and during time will be extracted. The less the thickness the Thermowood is, the less the distances between screws must be.
The flow of air behind thermowood is very important. These air flow can by applying underlying sawn timber (untreated) happen.
Normally the pine sawn timber only with a simple method of impregnation is enough.
Also the lengthening of thermowood and steel are different and steel as underlying surface of thermowood must be prevented. Instead can thermowood to underlying sawn timber screwed and underlying sawn timber to steel.
Coating:
Coating of thermowood with UV protected color is really vital as thermowood with UV will get gray. Normally water base color used on thermowood as it can save the pattern of wood and shapes of knots.
During time the color can be vanish so it is important the surfaces get recoated in 6 or 12 months intervals.
Applying tinted water base color can cause a little different in final color of thermowood and it is natural and unpreventable.
The waterborne color can be applied on both thermowood and sawn timber. But the color in theses mentioned surfaces are totally different.