Osmo WR Base Coat (4001) 2.5L
Osmo WR Base Coat 4001 (2.5L) is a clear exterior wood primer that penetrates deeply to stabilise timber and repel water. Use it as the first coat on bare wood before finishing with an Osmo exterior topcoat. It is designed to help reduce swelling and shrinkage, improve dimensional stability and provide preventative protection against blue stain and wood-decay fungi. WR 4001 is not a final finish and must be over-coated.
Best for: softwood and hardwood joinery above ground—windows, frames, doors, cladding, fascias, pergolas, fences and garden buildings.
Key features
- Clear, penetrating exterior primer for bare wood
- Water-repellent; helps reduce swelling, shrinking and warping
- Preventative protection against blue stain and rot (biocidal product – use safely; always read the label)
- Microporous; allows timber to breathe for long-term stability
- Improves adhesion and performance of Osmo topcoats
- Size: 2.5 litres • Sheen: Clear/Invisible once over-coated
Recommended topcoats
Apply one of Osmo’s exterior finishes after WR 4001 has dried, such as Osmo Natural Oil Woodstain, Osmo Country Colour (opaque), or Osmo UV-Protection Oil for vertical cladding and joinery. Choose a tinted topcoat for additional UV resistance.
Preparation & application
- Ensure wood is clean, dry and bare. Remove greyed or previously painted/varnished surfaces back to sound timber.
- Stir well. Do not thin.
- Apply one thin, even coat by brush or paint pad with the grain. Work end-grains thoroughly.
- Allow to dry fully as directed on the tin before applying your chosen Osmo topcoat(s).
- WR 4001 is not suitable for ground-contact timber or as a stand-alone finish.
Coverage and drying vary with species, porosity and conditions—always follow the instructions on the container.
Frequently asked questions
Is WR Base Coat 4001 clear?
Yes. It is a clear primer that leaves the wood looking natural and is intended to be over-coated.
Do I still need a finishing coat?
Yes. WR 4001 is a base/impregnation coat only. Finish with an appropriate Osmo exterior product for colour, UV resistance and ongoing protection.
Where can I use it?
Exterior joinery above ground: windows, doors, cladding, fascias, sheds and pergolas. Not for decking or direct ground contact.
Why choose Osmo WR 4001?
Using a dedicated primer creates a stable base that resists moisture uptake and supports the performance of your finishing coats. The result is tidy application, better durability and simpler future maintenance.
