Osmo WR Base Coat Clear (4001)

Additional Protection Beneath Your Exterior Finish

Exterior wood is exposed to moisture, changing temperatures and biological attack. Osmo WR Base Coat penetrates beneath the surface and provides preventative protection before the timber receives its final decorative coating.

Unlike an exterior topcoat, it does not provide the finished colour, sheen or full UV resistance required for exposed timber. Its role is to protect and prepare the wood beneath the final Osmo coating system.

Why Choose Osmo WR Base Coat?

• Preventative preservative for suitable exterior timber
• Protects against wood-rotting fungi
• Protects against wood-staining fungi and blue stain
• Protects against wood-destroying insects
• Penetrates deeply into the timber
• Provides additional moisture protection
• Extremely water-repellent
• Helps reduce timber swelling and shrinkage
• Particularly recommended for exterior softwood
• Suitable beneath compatible Osmo exterior finishes
• Suitable for windows, doors, cladding and garden structures
• Can be applied to all sides before installation
• Improves the prepared surface for subsequent finishing
• Can help regulate absorption on rough or absorbent timber
• Clear formulation does not provide decorative colour
• Normally requires no future maintenance once correctly overcoated

What Is WR Base Coat Designed to Do?

WR Base Coat 4001 vs WR Base Coat Aqua

Which Osmo Topcoat Should I Use?

Suitable Exterior Applications

• Timber cladding and façades
• Exterior wooden windows
• Exterior doors
• Window shutters
• Carports
• Pergolas
• Balcony railings
• Exterior fencing
• Privacy screens
• Summerhouses
• Garden buildings
• Suitable garden furniture
• Vertical softwood structures
• Hidden faces and edges of exterior joinery
• End grain before the specified finishing system

Suitable Timber

Timber species, previous treatment, natural oils, resin and moisture content can all influence absorption. Always complete a representative trial before treating the full project.

How Many Coats Are Required?

Osmo specifies an application quantity equivalent to approximately 160ml per square metre. Depending on the timber species, absorbency and surface characteristics, this quantity may be achieved in one, two or three controlled applications.

Coverage and Available Sizes

Coverage is based on approximately 5–6m² per litre. Actual consumption varies substantially according to timber species, porosity, texture and preparation. Rough-sawn and weathered timber may use considerably more.

Technical Information

Coverage and drying times are approximate. Temperature, humidity, timber species, surface texture, airflow and application quantity will affect the result.

Best Conditions for Application

• Apply to clean, dry and frost-free timber.
• Timber moisture content must not exceed approximately 20%.
• Apply between approximately 10°C and 30°C.
• Do not apply during damp conditions.
• Do not apply when rain is imminent.
• Protect freshly treated timber from rain while drying.
• Maintain good ventilation during application and drying.
• Protect soil, plants, drains and watercourses from splashes.

Surface Preparation

• Ensure the timber is clean, dry, absorbent and free from frost.
• Confirm that moisture content is no more than approximately 20%.
• Completely remove paint, varnish, lacquer and other film-forming coatings.
• Thoroughly clean compatible old microporous stains where renovation is appropriate.
• Allow new resinous, oily or pressure-treated timber to weather or dry as required.
• Repair or replace rotten, structurally damaged or unstable timber before coating.
• Use galvanised or corrosion-resistant fixings wherever appropriate.
• Remove all sanding dust before application.
• Stir WR Base Coat thoroughly. Do not thin.
• Protect plants, soil, water storage and nearby surfaces from splashes.
• Complete a representative trial before treating the full area.

How to Apply Osmo WR Base Coat

1. Confirm that the timber is clean, dry, frost-free and ready to absorb the preservative.
2. Stir the product thoroughly. Do not thin.
3. Protect surrounding soil, plants, paving, drains and watercourses.
4. Apply evenly with an Osmo Flat Brush or suitable microfibre roller.
5. Work along the wood grain and distribute the product consistently.
6. Apply to all faces, edges and concealed areas before installation where practical.
7. Pay particular attention to joints, end grain, cut edges and hidden surfaces.
8. Achieve the required total application quantity without leaving runs, puddles or heavy deposits.
9. Remove any excess from edges before it dries.
10. Allow approximately 12 hours’ drying with good ventilation.
11. De-nib lightly if the Base Coat raises the timber grain.
12. Apply the selected compatible Osmo exterior topcoat once the Base Coat is completely dry.

Protecting End Grain

End grain absorbs moisture far more rapidly than the main face of timber. WR Base Coat should be worked carefully into exposed cut ends before the full decorative system is applied.

For enhanced protection of exposed timber ends, complete the system with Osmo End Grain Sealing Wax 5735 where appropriate.

Recommended Application Tools

Recommended Accessories

Drying and Overcoating

Safety and Environmental Guidance

• Use only for the exterior applications stated by the manufacturer.
• Always read the current product label before use.
• Wear suitable protective gloves, clothing and eye protection.
• Do not eat, drink or smoke during application.
• Keep children and unprotected people away from the working area.
• Keep animals away until the treated surface is completely dry.
• Do not contaminate food, utensils or food-contact surfaces.
• Do not allow the liquid product to enter drains or watercourses.
• Protect plants, soil, ponds and aquatic environments from splashes.
• Do not use on beehives or beekeeping equipment.
• Check for protected bats before treating any potentially occupied structure.
• Dispose of the product and container responsibly.

Important Application Notes

• Use only on suitable exterior timber.
• Do not use on interior woodwork.
• Do not use on timber in permanent ground or water contact.
• WR Base Coat is not a standalone finished coating.
• A compatible Osmo exterior topcoat must follow.
• Apply the required total quantity evenly.
• The number of applications may vary according to timber absorbency.
• Apply on all sides before installation wherever practical.
• Timber moisture content must not exceed approximately 20%.
• Do not thin the product.
• Apply only in suitable dry weather.
• Protect freshly treated timber from rain.
• Do not contaminate soil, plants, drains or watercourses.
• Completely remove paints and lacquers before application.
• Use corrosion-resistant fixings where appropriate.
• Allow approximately 12 hours’ drying.
• Always complete a representative trial.

Tool Cleaning

Clean suitable brushes, rollers and reusable application tools immediately after use with Osmo Brush Cleaner & Thinner .

Do not wash preservative residues into sinks, drains, soil or watercourses. Dispose of cleaning residues in accordance with the current safety and local waste guidance.

Complete Your Exterior Timber System