In Denmark microwave treatment of timber has been used during the last 15 years for eradication of dry rot (Serpula lacrymans). About 1500 microwave treatments have been employed in coorporation with Hussvamp Laboratoriet. Previously all the infected timber was removed plus an extra metre as a safety zone. This meant that all casting boards and plaster had to be removed as well and joists replaced. The cost of such a replacement would often amount to several thousand Danish kroner (100 Dkr . 14 Euro). In cases with sufficient residual strenght of infected timber the cost can be reduced by 40-50% with microwave treatment. Very often it is necessary to support the construction with a fishplate of pressure impregnated wood. Theoretically the lethal temperature for mycelia of Serpula lacrymans is 37°C during 10 minutes, but to ensure that also resting mycelia are killed a temperature of 75°C is used. In order to ensure a sufficient quality of the treatment a thermo controll method has been developed by Hussvamp Laboratoriet whereby the temperature reached inside the wood is registred. In a joist a hole with a diameter of 13 mm is drilled from the side to the centre. A TERMAX or RS 285-936 irreversible temperature sensitive label is placed inside a piece of plastic tube, 6 cm long and 12 mm across, which is inserted into the hole. This is then closed with a corkplug with a diameter of 14 mm and 22 mm long. Afterwards the plug is sealed with a label carrying the logo of Hussvamp Laboratoriet and the text 'Hussvamp Laboratoriets Termokontrol'. The thermo control can be employed at the same time as the attack is delimited or at the start of repair work. After the microwave treatment the seal is removed and the corkplug is pulled out with a corkscrew. The tube with the temperature label is pulled out with a pair of tweezers. On the label the white markings turn black when the indicated temperature is reached. The markings for 65°C, 71°C and 77°C should be black in order to approve the microwave treatment. The method can also be used for other kinds of heat treatment of timber.

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