Why do I need to re-treat cut ends of treated timber?
All preservative treated softwood products are impregnated in their finished form in an industrial process and are designed to be installed without modification.
For this reason, re-working a treated component at the installation site should be avoided and limited to cross cutting, boring, drilling or notching.
Treated wood must NEVER be rip sawn along its length.
If a treated component does need to be cross-cut to size, bored, drilled or notched, any new exposed surfaces should be given two liberal brush coats of a suitable end grain wood preservative – to preserve the integrity of the original treatment.
Your timber supplier should be able to recommend a suitable product to use – ideally from the manufacturer of the preservative used in the original treatment. But if not then several TDCA members supply Cut-End Timber Treatment Products - go to Suppliers.
It is important to remember that the preservative penetration achieved by brush application is less than that achieved in the industrial treatment process.
So even if an end grain preservative has been applied to a cross-cut end of a treated post, this end must NEVER be embedded in the ground. Instead put the un-cut end in the ground.
If a post does needs shortening, then cut the top (at an angle to shed water) and apply two coats of brush-on treatment. You could also fit the cut top with a cap.