Microwaves as a Remedial Treatment of Wood

Abstract

A pilot experiment of microwave treatment was carried out on an Art Nouveau residential building erected at the beginning of the 20th century in Valencia, Spain. The timber structure was affected by a combined damage caused by Anobium punctatum (common furniture beetle or common house borer) and Kalotermes flavicollis (yellownecked dry-wood termite). After performing an exhaustive preliminary study on the building and analyzing the different alternatives of wood treatment, it was decided to use a microwave machine especially designed to eliminate this type of wood boring insects. This machine generates microwaves, a type of electromagnetic radiation, with a frequency of 2.45 GHz. This circumstance makes it possible to produce a high-frequency alternating electric field that causes the rotation of the molecular dipoles of water. Because of this continuous rotation the temperature of the water rises considerably. By heating up the humidity inside a living being, as in the case of xylophagous insects, an artificial fever in the body is generated, and since the animal is not capable of tolerating this temperature, it dies. In order to eliminate xylophagous insects, the wood moisture content (usually between 10% and 12%) and the presence of water in wood boring insects (around 90%) must be taken into account. Due to the greater content of humidity the increase of the temperature is higher and quicker in insects than wood. Prior to this pilot intervention, several research works were carried out with the same microwave machine, especially on wooden works of art. In all these studies it was observed that no damage was caused either to the wood or to the finish of the works of art including pigments, polishes, stains etc. On the other hand, 100% efficacy was achieved in the elimination of xylophagous insects. This article describes the design, experimentation and perfecting process of this microwave machine and its pilot application on structural timber in an Art Nouveau residential building. Bringing the knowledge of the laboratory on-site and assessing the differences in the procedures.