to marine borers that can enter the wood in very small cracks or exposed 



areas . 



c. Piles, 



(1) General . The principal woods used for piling are southern pine 

 and coastal Douglas fir, although a few other woods, such as red pine, 

 lodgepole pine, western larch, and oak, are used in some localities. No 

 untreated wood, commercially available for pilings, either domestic or 

 imported, will resist borer attack for more than several years. However, one 

 species of tropical tree known as greenheart (Oootea rodiaei or Neotandra 

 rodiaei) , which is not treatable, may last 2 or 3 years longer than treated 

 Douglas fir, in the same water. Timber piles should conform to the require- 

 ments of ASTM Standard D25. 



Untreated pine and fir piles usually last no longer than 2 years in the 

 ocean, often less than 1 year where marine borers, such as L. tvipunctata, 

 are present in great numbers. Treated piles have a life expectancy averaging 

 8 to 10 years where tripunctata are present. Limnoria tripunctata was selected 

 as an example because this is the only known species of Limnoria which will 

 attack and destroy heavily creosoted piling (Civil Engineering Laboratory (CEL) , 

 1974)) . 



The Forest Products Laboratory has tested a large number of preservatives 

 to study their effectiveness in protecting wood against marine borers. 

 Results obtained in these experiments, as well as experience in general, 

 have shown that heavy retentions of coal-tar creosote are essential if the 

 best protection is to be obtained (USDA, 1952) . The heavy retentions ensure 

 better penetrations and also furnish a reserve supply of creosote to provide 

 against early depletion by leaching. Over much of the coastal region of the 

 United States, marine timbers are exposed to severe borer attack, and it is 

 poor economy to specify retentions that will not give the maximum protection 

 under such conditions. Specifications for such timbers should require 

 treatment to refusal by the full-cell process, and the specified retention 

 should be the minimum that will be accepted. No maximum should be specified. 



The Civil Engineering Laboratory (CEL, 1974) reports that a compound that 

 is toxic to L. tripunctata does not prevent Teredo diegensis attack and a 

 compound that is toxic to T. diegensis is not effective against L. tripunctata. 

 Experiments by CEL indicate that a dual treatment of wood piles should be 

 used in moderate or warm waters to effectively defend against marine borer 

 attack. The dual treatment consists of metallic salts, either ammoniacal 

 copper arsenate (ACA) or chromated copper arsenate (CCA) and coal-tar creo- 

 sote. A 157-newton per cubic meter (1.0 pound per cubic foot) treatment of 

 metallic salts is applied in water solution. After drying, the wood is 

 pressure treated with coal-tar creosote to a 3 140-newton per cubic meter 

 (20 pound per cubic foot) retention. The above treatment may be specified 

 as conforming to American Wood Preservers Association Standard C3. This 

 treatment significantly increases the expected life of wood piles used in 

 moderate or warm waters but it also reduces the strength and toughness of 

 the wood. Eaton, Drelicharz and Roe (1978) of the Civil Engineering Labora- 

 tory report that dual -treated piles lose 27 to 54 percent of their untreated 

 flexural strength, measured as modulus of rupture, and about 50 percent of 

 their untreated flexural toughness, measured as energy absorbed per unit 



260 



