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High temperature drying, ie., drying above the boiling point of water, is the dominant method for the drying of radiata pine (Industry Standard 100-1992). If the correct schedule is followed radiata pine can be rapidly dried at temperatures in excess of 100 degrees centigrade with a minimum of degrade. Two methods of high temperature drying are used. The first method uses super heated steam. The dry bulb temperature is above 100 degrees centigrade and the wet bulb is at 100 degrees centigrade. Pressure is increased within the kiln to increase the dry bulb temperature. Although this method is rarely used there is increasing use of high temperature drying using steam/air mixtures. This method which is used to dry radiata pine in Australia is described below;

• Preparation.
  The initial moisture content of the timber should be green to ensure effective plasticisation of the timber at high temperatures. If the wood is likely to air dry before kiln drying commences then the wood should be block stacked and sprayed with water. Stacks are constructed as in normal kiln drying but the stack should be restrained with a load not less than 980 kg/cubic metres applied evenly over the top of the stack. Restraint has a major effect in reducing twist.

• Plasticisation.
  Directly prior to drying stacks should be steamed for four hours in saturated conditions at a temperature of not less than 95 degrees centigrade.

• Drying.
  Immediately after plasticisation the timber is dried until its moisture content is 6% on average and 10% maximum with the kiln conditions as follows.
  • Maximum dry bulb temperature between 116-160 degrees centigrade
  • Minimum wet bulb temperature 70 degrees centigrade
  • Minimum average air velocity within the stack, 4.0 m/sec, 5.0 may be the optimum

• Final conditioning.
  Immediately following drying, the timber is cooled to a surface temperature of between 90-100 degrees centigrade and then steamed under saturated conditions for four hours at a temperature of not less than 95 degrees centigrade.