When preservation has been specified, there is obviously a responsibility on the part of the contractor to make sure that the specification has been met. Many of the organic solvent based preservatives carry a faint tracer dye (often light reddish brown) but some manufacturers use a clear preservative. With COSHH regulations now in force, much of the telltale oily smell of organic solvent preservative will have evaporated by the time the trusses arrive on site. These regulations require safe handling of preservative treated timber to protect operatives from the chemicals contained in the preservatives themselves. This means a delay of some 48 hours between treatment and handling the timber to manufacture the trussed rafter. Some manufacturers overcome this delay by pretreating all timber stock, but then cut ends exposing untreated timber have to be swabbed with preservative before assembly. If specifying treated timber trussed rafters the purchaser should be aware of a slightly longer delivery time required by some manufacturers.
Identification of organic solvent treated timber may be possible by smelling the trussed rafters, especially towards the middle of the pack as they are delivered on the vehicle; these trusses will not have evaporated quite so much solvent and will give the distinctive oily smell of the organic solvent. Alternatively, a sliver of timber cut from the corner of one of the truss components exposing a fresh surface may indicate treatment. Finally, if in doubt, simple preservative testing kits are available from most of the preservative manufacturers, if any doubt exists. For security it is best to specify that the trussed rafter manufacturer provides a signed certificate of treatment for the trusses in any one consignment.
The waterborne preservatives have little odour, identification is therefore more difficult but there are tests available and reference should be made to the manufacturers of the treatment process if any doubt exists; if for instance a certificate has not been provided or in an attempt to ascertain the state of timber in an existing roof structure.
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