Relative efficacy of heartwood extracts and proprietory wood preservatives as wood protectants

Abstract

The relative potentials of either heartwood extracts (air dry extracts in 60 percent methanol) of very durable woods (Afzelia africana J.E. Smith;Erythrophleum suaveolens (Guill & Perr.) Brenam. Syn.E guinensis G.Don. orMilicia excelsa (Welw) C.C. Berg. Syn.Chlorophora excelsa (Welw) Benth.) or any of two proprietary wood preservatives (AWPA type “C”-Chromated Copper Arsenate (CCA) or 5 percent solution of AWPA Standard Designation P “9” type “C”—Pentanchlorophenol (Penta) in light oil solvent) to suppress attack on pressure treatedAntiaris toxicaria Lesch Sapwood by either any of three species of decaying fungi (Coridopsis Polyzona Klotzch;Lenzites trabea; orTrametes cingulata Fr.) under soil block exposure conditions were investigated and threshold values determined. Extract/preservative dosages were either 8.009; 24.778; 48.056; 96.111 or 144.167 kg m−3 (0.5; 1.5; 3.0; 6.0 or 9.0 1b/ft3). Exposure was for either 14 or 28 weeks and in accordance with ASTM D1413-72 Provisions. Conclusions reached were that at threshold values the ability of either any of the heartwood extracts or proprietary wood preservatives to suppress attack under conditions in this study was significant at 0.01. Relative efficacy of those biocides was dependent on fungal species. Neither any of the heartwood extracts nor any of the proprietary wood preservatives (except in the case ofTrametes cingulata attack on CCA treated wood at highest retention level) was able to confer “very durable” rating on treated wood. Possible reasons for the reduced relative durability of extracts visa vis native heartwood were advanced. At the highest retention level (144.167 kg m−3) there was no significant difference (at 0.05 level) between efficacy of each of the heartwood extracts and any of the proprietary wood preservatives (CCA or Penta).