Deterioration of imported timber by marine borers along Visakhapatnam tropical harbour, India

• Marine structures with timbers exposed below the water line are subject to attack by marine borers.
• Naturally durable timbers are used for marine construction to overcome the problem.
• Decline in the availability of naturally durable timber species resulted in the import of timber.
• Natural resistance of imported woods against marine borers was conducted at Visakhapatnam harbour.
• Performance of the imported timbers was found to be quite satisfactory.

For some time now, timber has been relegated to the back stage due to competition from modern alternatives. Yet, this lone renewable structural material is all set to stage a comeback soon because of the carbon benefits accruing from its use. Although India is blessed with over 4000 woody plant species, the country is timber deficient. In order to bridge the gap between supplies and demand, timber from different countries is being imported. But the performance of such timbers under various service conditions in different Indian environments is not known. Since information on these lines is desirable to put any timber to its best end-use, evaluation of the bioresistance of some of the imported timbers in marine regime was included in a larger programme and the results of this marine component are presented in this paper. A total of twenty timbers that originated from eleven countries together with two Indian timbers were subjected to marine exposure trial in Visakhapatnam tropical waters. The trial followed by data analysis distinguished the twenty imported timbers into five groups, viz., A. pseudoplatanus and Fagus sylvatica from Belgium with 8 months durability; A. pseudoplatanus, Fagus grandifolia, F. sylvatica and Fraxinus angustifolia from France and Havea brasiliensis from India with 9 months longevity; Fraxinus excelsior (Belgium) and Quercus robur (France) with 10 months life; Michelia champaka (India) and Shorea macroptera (Malaysia) with 14 months longevity and Dryobalanops aromatica (Malaysia), Pteocarpus soyauxii (Africa and Cameroon), Shorea s (Indonesia), Shorea robusta (Malaysia), Tectona grandis (Australia, Burma, Ghana, Ivory coast and Tanzania) and Xylia dolabriformis (Burma) with 18 months durability. Compared to the natural resistance of fifty-eight Indian timbers assessed earlier by various workers in the same harbour, performance of the twenty imported timbers tested now is considered as only moderate. While European timbers are advised to be used as marine structural components not in contact with sea water, others may be used universally in all marine applications. However, all the twenty imported timbers had exhibited inferior durability than Dalbergia sisoo, Diospyros melanoxylon, Kingiodendron pinnatum, Lagerstroemia hypoleuca, Lagerstroemia parviflora, Mimusops littoralis, Pterocarpus dalbergioides, Pterocarpus marsupium, Schleichera oleosa, S. robusta, Terminalia arjuna and Terminalia paniculata.