Comparison of disodium octaborate tetrahydrate-based and tannin-boron-based formulations as fire retardant for wood structures

Boron-based formulations are used to improve the service life of timber. On the one hand, boron-treated wood increases resistance to biological attacks (e.g. by fungi and insects), and on the other hand, it renders wood more resistant to burning. In the present study, we analyse the fire behaviour of some water-borne formulations containing boron. A completely inorganic formulation (disodium octaborate tetrahydrate (DOT)) is compared with new-generation tannin-based wood preservatives in which the flavonoid network is used to fix the boron to wood. The study of the fire behaviour was carried out according to four specific fire tests: (i) dripping; (ii) short-term exposure; (iii) long-term exposure and (iv) the limiting oxygen index. The Scots pine (Pinus sylvestris L.) specimens treated with DOT have shown a complete efficacy against fire after all tests were completed. It should also be noted that very positive results have also been achieved by the tannin-based solutions. DOT has to be preferred when high performance is required, but exclusively for interior applications. The use of tannin-based formulations can be suitable for outdoor fire protection and also for indoor applications when specific aesthetic requirements should be fulfilled. Copyright © 2013 John Wiley & Sons, Ltd.