Best Exterior Wood Primer for Sash Window Restoration: 2025 Expert Review
DR Joinery
Expert Joiner & Restoration Specialist
If there is one mistake I see homeowners make repeatedly with sash windows, it is rushing the preparation. You can buy the most expensive topcoat in the world, but if you apply it over a poor primer—or worse, bare grey timber—it will flake within a year. Here in York, our damp climate is unforgiving to shortcuts.
As a joiner, I distinguish between 'carpentry' which is structural, and 'joinery' which requires a finer finish. Sash windows fall firmly into joinery. The tolerances are tight, and the timber expands and contracts with the seasons. The primer needs to penetrate the grain to create a chemical key, sealing the wood against moisture ingress whilst allowing flexibility.
In this 2025 review, I am looking at three primers I frequently encounter on site. I have categorised them into a budget trade option, a high-end consumer choice for smooth finishes, and a versatile quick-dry solution for when the weather is turning.
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Specs vs. The Real World
The Spec: "2-in-1 Primer & Undercoat Claims"
"Marketing suggests one tin does both jobs perfectly, saving you money and time."
Whilst good for sound timber, on bare or repaired wood, a dedicated primer often penetrates deeper. For ongoing maintenance they are fine, but for raw timber repairs, check the adhesion carefully.
The Spec: "Quick Drying Times (1 Hour)"
"You can repoint, prime, and paint an entire window in an afternoon."
In a cold, damp Yorkshire spring, 'quick dry' water-based paints can inhibit proper absorption into the grain compared to slower oil-based traditional primers. Speed isn't always quality.
My Top 3 Recommendations
Three options to cover different needs and budgets
Leyland Trade Wood Primer - White 750ml
Leyland
This is a classic 'does what it says on the tin' product. Leyland Trade is a staple in the van because it offers honest performance at a very low price point. It is excellent for sealing bare timber ledges and sills where you need deep penetration rather than just a surface film.
The Good
- Excellent value for money
- Good penetration into softwood grain
- Levels well for a decent finish
The Bad
- Slower drying time compared to modern acrylics
- Stronger odour during application
Installer Tip:
On old resinous pine sashes, make sure you treat knots with a knotting solution before applying this primer, otherwise the resin will bleed through and ruin your white gloss finish.
Priced at £6.20 at the time of writing
Check Price on AmazonDulux Primer & Undercoat Paint For Wood - 750Ml, White
Dulux
Dulux has created a very user-friendly product here. Being water-based, it is low odour and easy to clean up, which is a blessing when working in occupied bedrooms. It acts as both primer and undercoat, building a solid opacity that makes the topcoat look fantastic.
The Good
- Low odour makes it ideal for indoor sash faces
- Quick drying allows for multiple coats in one day
- Brushes wash out in water
The Bad
- Significantly more expensive per litre
- Can raise the grain slightly on very soft timber
Installer Tip:
Because this is water-based, give the timber a light sand between coats with fine 180-grit paper. Water-based paints can cause wood fibres to stand up ('grain raising'), and a quick de-nib ensures your final gloss coat is glass-smooth.
Priced at £15.99 at the time of writing
Check Price on AmazonJohnstone's - Quick Dry Gloss Primer Undercoat - Brilliant White - 0.75 L
Johnstone's
When the weather in York is changeable, waiting 16 hours for an oil primer to dry is risky. Johnstone's solves this with a 1-2 hour drying time. It is also non-yellowing and versatile enough to use on masonry beads or metal fittings, making it a great all-rounder for complex restoration jobs.
The Good
- Rapid 1-2 hour drying time
- Non-yellowing formulation keeps white sashes bright
- Versatile: adheres to wood, metal, and masonry
The Bad
- Requires careful surface prep to ensure adhesion
- Not as penetrating as traditional oil solvents
Installer Tip:
Use a good quality synthetic brush with this primer. Natural bristle brushes tend to absorb the water content and become floppy, leaving brush marks. A synthetic brush will help lay the paint off smoothly for a professional joinery finish.
Priced at £8.97 at the time of writing
Check Price on AmazonFrequently Asked Questions
Should I use oil-based or water-based primer for exterior sashes?
Do I need to knot old sash windows before priming?
Can I paint over rot if I use a good primer?
How many coats of primer do I need?
When should I call a professional joiner?
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