Creosote and creosote-coal tar mixtures are commonly employed for sawed 

 material (such as bridge timbers) used under relatively severe conditions. 

 Retentions specified for such timbers vary from about 942 to 3 927 newtons 

 per cubic meter (6 to 25 pounds per cubic foot), about 1 570 to 1 890 newtons 

 (10 to 12 pounds) being most common. Both empty-cell and full-cell methods 

 are employed, depending on the amount of sapwood, retention required, size 

 of timbers, and similar factors. The full-cell process is commonly employed 

 in the treatment of resistant heartwood timbers and timber for use in salt- 

 water. 



Waterborne salts are widely applied in the treatment of sawed lumber 

 under conditions that make it impractical to employ preservative oils. 



Specifications for retentions of both preservative oils and water-borne 

 salts often fail to take into consideration the relation of the timber 

 dimensions to penetration and retention. The specifications may require a 

 net retention in large heartwood timbers that cannot be obtained because of 

 the small ratio of surface area to volume, although the same retention might 

 be obtained without difficulty in heartwood timbers of tie size or smaller 

 or in large-size timbers containing a large proportion of sapwood. In 

 timbers containing 50 percent or more sapwood, it is recommended that at 

 least 1 570 newtons per cubic meter of preservative oil be specified. 



(b) Retention by Penetration . The AWPA standards for adequate 

 penetration of the preservative indicate the required penetration in inches or 

 percent of the thickness of the sapwood, whichever is greater. Penetration 

 requirement of preservatives in timbers and lumber generally varies according 

 to species. However, for some species it also varies by size. Timbers and 

 lumber smaller than 5 inches (127 millimeters) require less penetration when 

 the species is coastal Douglas fir, hemlock or pine species other than south- 

 ern pine and ponderosa. Requirements for penetration are found in tables of 

 AWPA Standard C2. The following are representative examples of preservative 

 penetration requirements found in the tables. For use above ground or in 

 freshwater, the penetration required for southern pine is 63.5 millimeters 

 (2.5 inches) or 85 percent of the sapwood for all sizes. Coastal Douglas fir 

 would require a penetration of 12.7 millimeters (0.5 inch) and 90 percent of 

 the sapwood for sizes 5 inches (127 millimeters) and larger but for sizes 

 under 5 inches the requirements would be 10.16 millimeters (0.4 inch) and 90 

 percent of the sapwood. Oak, for the same uses, would have only the percent- 

 age requirement with white oak requiring 95 percent of sapwood and red oak 

 requiring 65 percent of annual rings. In the marine environment, the penetra- 

 tion requirements would be similar for each preservative of the dual treatment, 



(c) Treatment of Cuts and Holes . Insofar as practical, wood 

 pieces should be trimmed, dapped, bored and counterbored before pressure 

 treatment because field treatment cannot match the thorough penetration and 

 distribution of preservatives obtainable in the pressure retort. However, 

 it is not always possible and practical to avoid all field cuts and bores. 

 When pretreated wood is cut in the field it is essential that the exposed 

 wood be generously mopped with the same preservatives. The top faces of 

 field cuts are particularly vulnerable to fungus attack and should be given 

 extra careful field treatment. Wood submerged in saltwater is vulnerable 



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