Fire Retardancy of Fire-retardant-impregnated Wood after Natural Weathering III.Fire performance after 10-years exposure

Fire retardant-treated(FRT)wood with a series of phosphoric acid and amino resin(leach-resistant type)or a mixture of phosphoric acid and boric acid(indoor use type)was weathered for up to 10 years at three places in Japan. Test results showed that FRT wood with a series of phosphoric acid and amino resin had high chemical retention and fire retardancy after 10 years compared with FRT wood with a mixture of phosphoric acid and boric acid. From 5 to 10 years, Decrease in fire retardancy of uncoated FRT wood treated with each fire-retardant was slower than up to 5 years. Fire retardancy of FRT woods with each fire retardant after 10 years, increased by coating with combination of fluorine resin-based and polybutadiene-based paint. FRT wood with a series of phosphoric acid and amino resin might keep initial fire retardancy for 10 years, if coated with the above paint. For uncoated and coated FRT wood with a mixture of phosphoric acid and boric acid, it showed that fire retardancy after 10 years was influenced by weathering sites. The condition for setting up the weathering rack was considered the reason for the influence of the weathering site on fire retardancy of weathered FRT wood.