Should I prime a wood fence before painting?

Quick Answer

Yes, it is highly recommended to prime a new or previously painted wood fence before painting. Priming creates a uniform surface for the paint to adhere to, allows the topcoat to go on smoothly, and helps prevent tannins and other wood extractives from bleeding through the paint. Priming also seals the wood, protecting it from moisture damage. For best results, use an oil-based primer specifically formulated for exterior wood.

What is Priming?

Priming is the process of applying a base coat of primer to a surface before painting. Primers are specially formulated paint products designed to prepare surfaces for painting. The main purposes of priming are:

• To create a uniform surface for the paint to adhere to.
• To seal porous surfaces and prevent absorption of paint into the substrate.
• To block stains and prevent them from bleeding through the topcoat.
• To promote adhesion and longevity of the paint job.

Primers allow the topcoat of paint to go on smoothly and uniformly. They prevent bare patches and an uneven look. Priming is almost always recommended before painting wood, drywall, masonry and metal surfaces.

Advantages of Priming Wood

Some key benefits of priming wood before painting include:

• Seals the wood surface and prevents moisture absorption – This protects the wood from warping, cracking and rotting.
• Helps prevent tannin bleed – Tannins in wood can cause staining as they migrate through paint. A primer blocks tannins.
• Provides a uniform substrate – Ensures the paint goes on evenly without bare patches.
• Promotes adhesion – Primers bind well to wood and provide a surface paint can grip.
• Extends paint durability – Prevents moisture damage and paint peeling or cracking over time.
• Blocks existing stains – Prevents discoloration from knots, water damage or other stains from showing through the paint.

Should You Prime New Wood?

Priming new, unfinished exterior wood before painting is highly recommended. When bare wood is exposed to the elements, moisture and sunlight can break down its surface fibers. This creates an uneven, porous surface for paint. Priming seals the fresh wood and creates an even base for paint adhesion.

Priming new wood provides the following benefits:

• Seals and protects the wood from moisture damage
• Helps prevent cracking, warping and cupping
• Blocks natural wood discoloration and tannin bleed
• Provides a uniform surface so paint goes on evenly
• Promotes better adhesion and longer-lasting paint job

Some raw woods like cedar, redwood, pine and fir contain high levels of tannins, resins and natural oils. These can cause staining as they leach through paint. An oil-based primer is best for sealing in wood tannins. Always check the manufacturer’s recommendations and do a test patch before painting.

In summary, priming before painting new wood helps the paint last longer. It prevents many common problems with the appearance and performance of wood finish paints.

Should You Prime Previously Painted Wood?

It’s also a good idea to prime older wood fences before repainting. As exterior paint ages, it can crack, peel and become chalky. These issues create an irregular surface that new paint won’t adhere to well. Priming provides an even base and allows the new paint to bond tightly.

Reasons to prime a previously painted wood fence:

• Fills in cracks and evens out surface irregularities
• Adheres well to aged paint surfaces
• Provides a fresh base for the new paint
• Prevents the new paint from absorbing unevenly
• Blocks existing stains from bleeding through
• Promotes adhesion so paint lasts longer

Priming before repainting also allows you to spot prime any bare wood or problem areas before applying paint to the entire surface. This prevents localized failures in the new paint film.

In short, priming previously painted exterior wood ensures a more durable and uniform-looking paint job. It covers up flaws in the existing paint while providing the ideal surface for the new coat.

What Type of Primer Should I Use?

For best results on wood fences, use an exterior oil-based primer specifically formulated for wood. The advantages of oil-based primers are:

• Provide superior sealing and penetration on wood surfaces
• Adhere well to aged latex and oil-based paints
• Block tannins, knots and wood stains more effectively
• Create a harder, more water-resistant undercoat for the finish paint
• Resist chalking or peeling paint from bleeding through

Oil-based primers contain linseed oil or alkyd resins that penetrate and seal wood. This stops moisture absorption and swelling of the wood. Oil-based primers also offer excellent adhesion and flexibility. The longer drying time allows paint to settle smoothly over the primer.

Some top-quality oil-based primer options include:

• Zinsser Cover Stain Oil Primer
• KILZ Original Primer
• Zinsser B-I-N Shellac-Base Primer
• INSL-X Prime Lock
• Benjamin Moore Fresh Start Alkyd Primer

While latex primers are easier to apply and clean up, they don’t seal, penetrate or block stains as effectively. For priming exterior wood, oil-based primers are a better choice. Make sure to check the manufacturer’s recommended dry time before painting over an oil-based primer.

Preparing Wood Surfaces for Priming

Proper surface prep is key to achieving good results from priming and painting wood fences. Here are some tips for preparing wood:

• Repair any cracked or decayed boards, loose joints or missing nails.
• Remove peeling or cracked paint with scraper, putty knife or wire brush.
• Sand areas of exposed wood to smooth and remove fibers.
• Clean surface thoroughly with TSP substitute to remove dirt, mildew stains, chalky paint etc.
• Rinse with fresh water and let wood dry completely.
• Spot prime any knots, sap streaks or tannin stains.
• Caulk cracks and joints if needed.

Proper prep removes contaminants that could cause adhesion problems or bleed-through. It also smoothes the surface for an even coat of primer and paint.

How to Apply Wood Primer

When priming exterior wood, follow these best practices:

• Read and follow the primer manufacturer’s instructions.
• Use a nylon/polyester brush for oil-based primers.
• Apply primer when temperatures are between 50-90°F.
• Work a few boards at a time loading a generous amount of primer on the wood.
• Brush with the grain to fill any cracks or holes.
• Apply enough primer to seal the surface completely.
• Let primer dry fully before painting.
• Apply two coats if sealing severe stains, tannins, or changing colors.
• Clean brushes and supplies with mineral spirits or paint thinner.

Applying primer to exterior wood when temperatures are moderate allows for proper drying and penetration. Using the right brush and coating the boards fully creates an ideal foundation for the paint.

How Long to Wait Before Painting?

Oil-based primers take longer to dry than latex primers. The drying time depends on the specific brand, humidity levels and temperatures. Here are some general guidelines on dry times before painting:

• At 70°F and 50% humidity – 8 to 24 hours
• Cool and humid conditions – 48 hours or longer
• Hot, dry weather – 4 to 6 hours

Always check the manufacturer’s recommended recoat window for the primer. Test if the primer is fully cured by pressing your thumb firmly against it. If the primer feels dry and hard, it’s ready for paint.

Applying the finish too soon can cause blistering, wrinkling, lifting and poor adhesion as the primer continues to dry underneath. Be patient and allow ample drying time before painting primed exterior wood.

Priming Tips and Precautions

Here are some important tips for successfully priming wood fences:

• Wear protective equipment – oil-based primers contain solvents.
• Thin primer with mineral spirits for better penetration on porous woods.
• Mix primer well before and during use.
• Load paint generously and maintain a wet edge.
• Seal all end grains thoroughly.
• Use block fillers to seal knots for complete blocking.
• Prime the bottom edges of fence boards if possible.
• Allow 2-3 days curing for oil primer in cool weather before painting.

Avoid painting in direct sunlight or on dirty or damp wood surfaces. Adhering to the manufacturer’s instructions is also critical for success. With proper prep work and application, priming will ensure your wood fence paint job stands up to the elements.

Conclusion

Priming before painting a wood fence provides many important benefits. Oil-based primers are best for sealing, penetrating and blocking stains on exterior wood. They prevent moisture damage, stop tannin bleed-through, and create a uniform undercoat for the finish paint. Following the manufacturer’s recommendations for surface prep, application and dry times results in optimal adhesion and performance of the paint system. While adding a step, priming new or previously painted wood is well worth the time and effort. Utilizing the proper primer products and application techniques allows the paint to last longer and look great on exterior wood fences.

Type of Primer	Benefits
Oil-based	Penetrates wood better Blocks stains and tannins Creates a moisture resistant barrier Provides excellent adhesion
Latex	Dries faster Easier water cleanup Low odor Can be tinted

Recommended Oil-Based Wood Primers

Primer	Features
Zinsser B-I-N	Sticks to glossy surfaces Seals in tough stains Prevents tannin bleed
KILZ Original	Excellent adhesion Seals and blocks stains Prevents tannin bleed
Zinsser Cover Stain	Seals knots, sap streaks Sticks well to aged paint Prevents tannin bleed