Dual Treatment

Job specifications sometimes call for wood to be both fire retardant and preservative treated (dual-treated). There are several reasons why this is questionable.

1. Dual-treated wood cannot be certified as either fire retardant or preservative treated. No UL fire retardant flame spread classification mark can be applied, and no preservative identification mark can be applied to dual treated wood. Codes require third party identification marks, so this would not meet code requirements for either fire retardant treatment or preservative treatment.
2. Dual-treated wood has to be pressure treated and kiln dried twice, and the effect on strength is unknown.
3. Dual treatment is expensive because two separate treating/drying charges are assessed.
4. Exterior Fire-X treatment provides built-in decay resistance in above-ground uses. Pyro-Guard also has built-in decay resistance but it can only be used in interior dry conditions because the chemicals are somewhat water-soluble.

In outside applications, a yearly application of a water repellent preservative will help protect Exterior Fire-X wood from weathering. Some water-repellent preservatives are advertised as being paintable and would therefore be useful as a prime coat for stain or paint.