Genuine Dricon® FRT Wood – Hygroscopicity

The Dricon® formulation was developed specifically to overcome problems with hygroscopicity and corrosion, enabling greater opportunities for FRT wood in the truss industry. It is based on fire retardant chemicals having a high molecular weight and very limited solubility. The formulation has not been changed since its development in the 1970’s and commercial introduction in 1981.

A material which gains moisture from the atmosphere as the relative humidity increases is said to be hygroscopic. The more hygroscopic a material is, the more moisture it will pick up during periods of high humidity. Wood is naturally hygroscopic, and fire retardants can increase this property from very little to significantly. Thus, there is no such thing as non-hygroscopic FRT wood. Some fire retardants absorb excessive moisture which can create problems with appearance, surface finishing and corrosion of metal hardware. However, the Dricon formulation only slightly increases the hygroscopic properties of untreated wood.

The American Wood Protection Association standards differentiate between “low-hygroscopic” Type A products and other more hygroscopic Type B products. Type A products must remain at or below the fiber saturation point of wood (28% moisture content) when conditioned at 92% relative humidity and 80-degrees F. Furthermore, Type A products are differentiated by their intended application (i.e., Type A high temperature (HT) and Type A low temperature (LT). Dricon FRT wood is listed as an interior Type A (HT) product by AWPA.

In tests conducted in accordance with ASTM D 3201, there was very little difference between the moisture content of Dricon FRT wood and untreated wood. Even when the relative humidity was increased from the specified test level of 90% up to 96%, the difference remained slight. By comparison, typical conventionally treated samples had twice the moisture gain of untreated wood even below 85% relative humidity.