Use of preservative treated timber

Use of preservative treated timber requires special care during construction to maintain the efficiency of the treatment.

During construction, disturbance of the protective treated envelope must be minimised, particularly for incised or round timber. Preservative treatments do not generally extend completely throughout the timber, so cut surfaces can expose untreated timber.

Where possible, all cutting, drilling and notching should be conducted prior to treatment. If this is not possible, areas affected by on-site drilling, notching and cutting should be given supplementary on-site treatment by:

• for CCA or LOSP treatment: flood brushing with water repellent preservatives or application of a thick coating of a preservative paste (copper napthenate) emulsion
• for creosote: flood brush application of creosote oil or pigment emulsified creosote (PEC) emulsion

These procedures may also be considered for ongoing maintenance, however, effective chemical treatment can usually be considered permanent.

Reference:Timber Datafile P4 – Timber – Design for Durability of the NAFI Timber Manual.

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Timber Research Unit
Department of Architecture
University of Tasmania