Matt is a professional painter and freelance writer, sharing his knowledge, house-painting tips, and product reviews.
Painting with Oil-Based Primer
Whether you're painting stained cabinets, spindles, trim, or any other unpainted wood surface, using the right primer is critical for a successful paint job. The best primer for painting stained wood is one that's oil-based, not latex. While you might consider using the less stinky latex option, it is a bad choice for priming stained wood.
Latex primer raises the wood grain and doesn't form a seal to stop natural wood oil from discoloring paint. If you use white paint on bare oak, pine, or cherry, without priming first, oily stains will appear in the paint. The stains won't go away, even with multiple coats of paint applied. This is known as tannin bleed, and it is your enemy when painting wood.
Even though oil primer is messy to work with and smells bad, it's still one of the best options for priming unpainted wood. I have yet to find latex primer that matches the performance. Oil primer soaks into wood to form a seal without raising the grain, and wood tannin won't bleed into your paint. The primer also enhances paint gloss.
Painting Over Oil-Based Paint
If you plan to use latex paint on wood already painted with oil paint, do not paint it without applying one coat of oil-based primer first, or a latex bonding primer specified for use over oil paint. For the best adhesion, an oil-based bonding primer is the most reliable option. You can use any latex paint on top of it.
What happens if you use latex paint over oil paint without a prime coat? Latex paint bonds poorly with the hard and smooth surface of oil paint, resulting in peeling, or cracks in the finish. This might not happen right away, but it will over time. You would then be faced with the nightmare task of having to strip off all of the paint to start over.
Brushing Oil Primer Onto Wood Substrates
The quality of your prime quote is equally important as your paint coat. You can brush on a flawless coat of paint, but if the primer underneath is full of horrible brush strokes, the imperfections will be an eye sore. Brushing oil primer onto wood is more challenging than brushing on water-based primer. The added thickness makes it more tricky to work with. If you over-apply, or brush over the same wet area one too many times, you'll end up with a real mess. Follow my tips to avoid a headache.
Choose the right paint brush: Brushing on primer smoothly starts with a high quality paint brush meant for oil-based coatings. Don't use the wrong type of brush, or a low quality one. My personal favorite brush for oil-based coatings is the Purdy Black Bristle China Brush. The natural bristles hold more material to make cutting-in easier. I get multiple uses out of these brushes before I need to replace them. Careful cleaning is key. I soak my oil brushes in mineral spirits and clean the bristles with a wire brush. After cleaning, I wipe the bristles dry with a rag to prevent them from hardening.
Use the right size brush for what you're priming. A brush too big for a small area will be difficult and messy to work with. For most interior trim, I use an angled 2 to 2 1/2-inch brush. For narrow window sash, or working around door hinges and other small areas, a 1-inch brush is perfect.
Thin the primer: Oil-based primer is thick and sticky, and when used right out of the can without any thinning, you will end up with brush strokes because the primer gets tacky before it's had a chance to level out. For fine finishing projects, thinning is key for reducing brush strokes.
You can thin it by either adding a small amount of mineral spirits, or an extender like Penetrol. This extends the dry time to let the primer level out more before it starts drying. Extender also makes application easier because you have more working time.
Don't over-apply: A little goes a long way. Even after thinning, brushing on too much primer leaves brush strokes and uneven texturing in the finish that are hard to remove without sanding. Apply a small amount of primer first and see how far you can spread it evenly over the surface with your brush, working in sections. Always leave a wet edge and work in one direction, similar to staining a deck, or rolling paint onto a wall.
Over-application can also cause problems with the paint. If the primer underneath was applied heavily and hasn't cured enough, the paint on top can remain soft and sticky to the touch for an extended period of time, especially if a darker color was used. Always apply thin coats so the primer can dry normally before you paint over it.
Apply two coats: On most of my wood painting projects, I apply two coats of primer and two coats of paint. Two coats of primer eliminates any chance of tannin bleed. Sometimes the first coat doesn't completely seal the surface. Two coats is important too when priming over grain filler. With only one prime coat, you can run into problems with dull spots in the paint gloss.
Two prime coats also gives you optimal paint coverage when painting white over brown wood that hasn't been painted. The paint will cover so much easier in a couple coats. The gloss of the paint will also be more shiny and smooth.
What's the Best Oil-Based Wood Primer?
Anyone who follows my content knows I'm a big fan of primer from the Zinsser brand. They have some of the best products on the market for paint prep. One of my favorite oil-based products for brushing and rolling stained wood is Zinsser Cover Stain. Kilz Original is another good one I have used many times in the past, but I like Cover Stain because I can use it outdoors too.
If you have a Sherwin Williams store in your area, they're Pro Block primer is great for wood too, or the oil version of the Multi-Purpose Primer. Pro Block dries a little faster. Cover Stain usually costs less and sands easier.
Oil primer isn't the only option too for painting stained wood. One of the best stain blocking products to use on unpainted wood is Zinsser BIN, a shellac-based primer. I prefer oil over shellac-based primer for brush and roller application because it's less messy. For spraying unpainted wood, BIN is an excellent choice. It sprays like a dream and performs the same as an oil-based product.
Like most solvent-based coatings, all of these products have a strong odor that requires ventilation, especially when sprayed. I also recommend wearing a painting respirator to protect yourself from the fumes. The fumes will give you a headache in no time.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2020 Matt G.