A small laboratory study was carried out which demonstrated that dry wood dip treated in a high concentration borate solution could not be subsequently treated properly with oil borne copper naphthenate unless it was subsequently steam treated to accelerate borate penetration into the wood and re-dry the wood beforehand. A larger study with commercial sized cross ties (railway sleepers) was carried out to see if the same steaming approach could be successful in large dimensions, at a commercial treatment plant and with creosote. It was found that dry ties dip treated in a 25 % borate solution at ambient temperature easily met AWPA standard borate retention and railway specifications as determined by gauge and could then be subsequently and successfully creosote treated after a two hour steaming process. The steaming would not increase total treatment time in the cylinder as it could be considered part of the sterilization time and the treatment by dip had the advantage of treating all species approximately the same with regard to borate preservative retention, overcoming the weakness of pressure treating with borate which can reduce creosote penetration and retention by making the ties too wet and cannot properly treat the white oak and hickory ties to appropriate retentions when treated in the same charge as red oak ties. Some slight loss of borate seamed to occur as a result of steaming, as shown by assay, but the process was modified to avoid condensation in the process for full commercial adoption.

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