How to Prepare and Paint LOSP H3 Treated Pine Before Installation
Quick answer
Keep LOSP H3 treated pine dry, allow at least 72 hours after delivery for acclimatisation, and apply two thin coats of oil-based primer to all six sides before installation. Finish with compatible topcoats and inspect the coating annually.
LOSP H3 treated pine is specified for many exterior, above-ground decorative timber products. The preservative treatment and the paint coating are not substitutes for one another. The treatment addresses particular decay and insect risks; the coating protects exposed surfaces from weather and sunlight.
Always follow the instructions supplied with the product. The sequence below reflects Heritage Decorative Timber’s published preparation requirements and is intended as a practical overview.
Keep the timber dry and allow it to acclimatise
Store the product flat, supported and protected from rain. Heritage’s instructions call for at least 72 hours after delivery before painting. Do not wrap wet timber tightly or leave detailed components sitting on damp ground.
Prime all six faces
“All six faces” means front, back, both edges and both ends. On fretwork it also means every pierced cut. On an assembled balustrade it includes rebates and joints. On a gate it includes the top and bottom edges. These are often the areas that become inaccessible after installation.
Apply two thin coats of oil-based primer rather than one heavy coat. Heritage specifies oil-based primer because LOSP is a solvent-borne treatment system. Work the primer into end grain, cut-outs and shaped details without allowing thick runs to obscure the profile.
Finish with suitable topcoats
After the primer has cured as directed, apply two or three thin topcoats compatible with the primer and exposure. Follow the coating manufacturer’s drying times. Colour choice can affect heat absorption, so discuss unusually dark finishes if the component receives strong sun.
Do not cut an unsealed edge at installation
If a primed component must be trimmed, re-prime the fresh cut before fixing it. The same applies to drilled holes and damaged coating. Plan as much cutting and fitting as possible before the final coats so every exposed surface remains part of the coating system.
Know what the guarantee covers
Heritage Decorative Timber states its 25-year guarantee for external LOSP H3 treated pine used above ground and ties it to correct preparation and maintenance. It does not automatically extend to MDF, untreated clear pine, Merbau, CCA products, ply components or every item sold for a building.
Read the complete LOSP treated-pine painting instructions for the product-specific wording before work begins.
Inspect the finish every year
Look for checking, open joints, worn edges, impact damage and areas where water sits. Touch up failures promptly rather than waiting for widespread peeling. Pay particular attention to top edges, end grain and horizontal surfaces.
Preparation checklist
- Confirm the product material and exposure
- Keep it dry and allow the required acclimatisation period
- Prime every face, edge, end and pierced detail
- Use two thin oil-based primer coats as specified
- Apply compatible topcoats
- Seal any installation cuts or holes
- Inspect and maintain the coating annually
Careful preparation takes longer before installation, but that is when detailed timber is easiest to reach. Painting only what remains visible afterwards leaves the most vulnerable faces untreated.