Yes. Treat freshly cut ends, drilled holes and notches in pressure-treated timber with a suitable end-grain preservative. Factory treatment does not mean every newly exposed surface has the same preservative protection as the original exterior.
Apply two liberal brush coats to cross-cut ends
Timber Development UK, summarising Wood Protection Association guidance, recommends two liberal brush coats of a suitable end-grain preservative or protector to freshly exposed cut ends.
Drilled, bored and notched areas need treatment too
The same guidance applies where drilling, boring or notching exposes timber beneath the treated surface. Apply the cut-end product according to its manufacturer's instructions.
Do not bury a freshly cut post end
A brush-on treatment is not equivalent to the original industrial treatment. If a treated post needs shortening, cut it from the top where possible, treat the cut top and keep the original treated end for the ground-contact end. A cut end should not be embedded in the ground even after brush treatment.
Do not rip-saw treated timber along its length
UK guidance says treated timber should not be rip-sawn along its length because this can remove too much of the treated envelope. If the job needs a different section, buy the correct size rather than ripping a treated section down.
Plan cuts before installation
Cutting is sometimes unavoidable, but fewer unnecessary cuts mean fewer exposed areas to protect. Treat each required cut before the timber is closed into the job.
Source: Timber Development UK — Making preservative-treated timber last longer.
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