Remedial boron treatment of difficult to access timber in buildings

The quest to understand remedial treatment for timber framing began following the ‘leaky building crisis’ in New Zealand which came to prominence in late 1990s. Several in situ remedial treatment products are used in New Zealand. However, effectiveness of these treatments is still unclear, particularly in situations where not all faces of the timber can be accessed. This research was conducted to establish whether a ‘double coat brush-on’ or ‘double coat brush-on plus injection treatment between studs’ system would give the most surface coverage and retention of a commonly used remedial treatment chemical, boron. Results showed that in the ‘double coat brush-on’ process, the concealed surfaces were left largely untreated resulting in variable preservative retention between components and relatively low overall preservative retention in the multiple stud units. However, the ‘brush-on plus injection treatment’ application gave much better preservative spread onto concealed surfaces of both vertical and horizontal members. Most samples tested achieved average cross-section boron retention levels of 0.4 % BAE m/m (NZS 3640, H1.2 treatment specification), although the treatment was concentrated in the outer 30 % of the timber, hence not achieving the required full sapwood penetration. Because of the variability associated with the boron injection process, it is recommended that this remediation method should only be used where there is a high degree of confidence that there is no decay present between studs or lintel members. All attempts should be made to remove any decaying timber while repairing leaky buildings.