Painting can feel like both an art and a science. Knowing which types of paintwork together can make the difference between a paint job that withstands the test of time and one that starts peeling or cracking before it fully dries. When it comes to oil-based and latex paints, conventional wisdom says that oil-based should never go over latex. But is this always the case? Let’s look at the pros, cons, preparation, techniques, and alternatives for oil painting over latex.
Overview of Oil and Latex Paints
Before digging into the details of painting oil over latex, it helps to understand the fundamental differences between these two common paint types.
Oil-based paints consist of pigments suspended in a drying oil, usually linseed oil. The oil undergoes a chemical reaction as it oxidizes and hardens, which is what cures and binds the paint film. Oil paints have been used for centuries, prized for their glossy finish and durable, protective coating.
Latex paints use water as the carrier instead of oil. The pigments are suspended in an acrylic polymer emulsion. As the water evaporates, the polymers fuse as the paint film cures. Latex paints are designed to be more flexible and forgiving than oil paints. They’re also water-soluble when wet, making cleanup with soap and water easy.
Oil and latex paints have very different properties, mainly:
- Flexibility – Latex paints are more flexible and elastic. Oil paints are more rigid when dry.
- Curing process – Latex cures through water evaporation. Oil cures through oxidation as the oils crosslink.
- Clean up – Latex cleans up with water. Oil requires paint thinner or mineral spirits.
- Durability – Oil paints are generally more durable in the long run. Latex can deteriorate faster outdoors.
- VOC levels – Oil paints have higher VOCs from the petroleum-derived solvents. Latex paints have lower emissions.
Understanding these core differences helps illustrate why painting oil over latex can lead to potential adhesion problems.
The Problem With Painting Oil Over Latex
Paint adhesion depends heavily on the paint layers being compatible with one another. As a general rule, painting a flexible paint (like latex) over a rigid one (like oil) poses few issues. The flexible paint can stretch and move with the rigid layer underneath.
However, the reverse scenario—applying a rigid paint over a flexible one—often causes problems. As the flexible latex paint ages, it continues expanding, contracting, and moving. The rigid oil paint on top has trouble accommodating this movement, which can cause it to crack or peel.
There are a few key reasons why oil over latex can fail:
- Curing incompatibility – Oil paint cures through oxidation as the oils crosslink. Latex cures through water evaporation. These differing curing mechanisms can interfere with proper adhesion.
- Rigidity mismatch – The latex undercoat’s elasticity clashes with the oil topcoat’s rigidity, especially as temperatures fluctuate. This disparity puts stress on the paint layers.
- Bond failure – Even when cured, the slick surface of latex paint may give oil paint nothing to grip. This can cause delamination as the layers separate.
While oil over latex doesn’t work in theory, what about in practice? Will it adhere well enough for low-traffic areas or temporary fixes? Let’s explore real-world results next.
Does Painting Oil Over Latex Work?
Though not ideal in theory, some DIYers report success when painting thinned oil-based primers, enamels, or varnishes over cured latex. The oil layer adheres well initially and the paint job looks fine—leading people to declare victory.
However, oil over latex often fails in the long run. The inflexibility of the oil paint causes it to crack and peel—sometimes in a matter of months. Even if the paint doesn’t fully delaminate, it may develop an undesirable spiderweb pattern of cracks.
Painting oil straight over latex does work in some specific applications:
- Small touches ups – Using oil to spot paint repairs on old latex finishes can be effective. The small oil area bonds adequately to the surrounding latex.
- Low-traffic surfaces – Oil over latex may hold up better on ceilings or walls with little use. High-touch areas like trim and doors are prone to fail.
- Temporary solutions – For short-term fixes that don’t need to last, oil over latex offers convenience compared to stripping the old paint.
Oil generally doesn’t play well for long over latex—especially on highly-used surfaces. But is it ever advisable in certain situations? Let’s look at some professional insights.
What the Experts Say About Oil Over Latex
Both DIY sites and seasoned professionals generally agree—painting oil-based paints directly over latex paint leads to inferior results. Oil over latex tends to fail prematurely.
According to Jeff Jewitt, Home Depot’s resident painting expert, “Applying an oil-based paint over a latex paint can cause bubbling and peeling. The latex paint is more flexible and elastic, and the oil-based paint is quite rigid when dry.”
Many pros recommend avoiding oil over latex entirely. But some paint manufacturers offer tips for making it work in limited cases:
- Benjamin Moore states oil can go over latex only if the latex is fully cured and deglossed. Scuff sanding is required.
- Sherwin-Williams recommends an oil-based primer if repainting with oils. Oil straight over latex often fails.
- Behr says oil over latex works only for spot touch ups and low-traffic areas. All-over painting will likely peel.
- Rustoleum argues oil bonds fine to latex if the latex has properly cured for over 30 days.
Most experts agree thorough prep work is crucial if you must paint oil over latex. Next we’ll explore steps for prepping latex paint for an oil topcoat.
How to Prepare Latex Paint for an Oil Topcoat
To maximize adhesion, latex paint must be fully cured, cleaned, and deglossed before applying an oil-based paint. Plan on at least 2-3 days of prep work.
Here are tips for getting latex paint ready for an oil topcoat:
- Allow latex to cure fully – Latex paint continues curing and off-gassing for up to 30 days. Don’t topcoat with oils until latex has hardened completely.
- Clean and degrease – Use TSP or other cleaners to remove grease, grime, or wax from the latex surface. Rinse thoroughly.
- Sand to degloss – Use 120-220 grit sandpaper to scuff the surface. Dulling the sheen gives oils something to grip.
- Remove sanding dust – Wipe and rinse away all sanding debris, which can interfere with adhesion. Allow to fully dry.
- Spot prime – Use an oil-based primer to spot prime any repairs or unpainted areas on the surface.
- Apply adhesion promoter – Brush on a clear primer-sealer to increase surface grip for the oil paint.
Proper prep removes gloss, cleans away contaminants, and promotes better bonding. But even with preparation, painting oils directly over latex often underperforms. Using a special primer provides better results.
How to Use Primer When Painting Oils Over Latex
Professionals recommend applying an oil-based primer first rather than paint oil-based paints straight over latex. Primers act as intermediary layers that allow more compatibility between the latex and oil.
Two main options exist when priming for oil over latex:
1. Traditional oil-based primer
Traditional oil-based primers like Kilz and Zinsser Bulls Eye 123 provide good holdout and surface adhesion for oil paint. Allow the primer to cure for at least 24 hours before painting fully.
2. Waterborne alkyd primer
Waterborne alkyd primers like Zinsser Cover Stain and Benjamin Moore Fresh Start combine the adhesion of oils with the ease of water-based cleanup. They form an ideal bridge from latex to oil.
For both options, follow the manufacturer’s instructions for proper application over latex paint. While oil primers improve compatibility, using latex primers under oil paint remains problematic.
Alternatives to Painting Oils Directly Over Latex
If you want to avoid adhesion problems from oil over latex, consider these alternate approaches:
- Strip the latex completely – Removing old latex to the bare surface guarantees compatibility with new oil paint. But this requires major time and labor.
- Apply an oil-based primer – As discussed above, oil primers help new oil paint adhere to old latex surfaces.
- Repaint with latex – Covering oil paint with another coat of latex poses no adhesion issues. Or use latex for the topcoat and reserve oils for the primer.
- Use an oil and latex hybrid paint – Many new latex paints contain alkyd additives for better flow and adhesion. These “hybrid” latex paints bond well to old oil or latex finishes.
- Hire a professional – Experienced painters have the know-how to assess paint compatibility and tackle any preparation needed to get the right results. This option costs more but saves you the hassle.
- Test adhesion first – Try a small test patch of oil over latex in an inconspicuous area before committing to a full paint job. Check after a week or longer to see if cracking or peeling occurs.
Weigh the pros and cons of each approach for your particular painting project. Removing all latex or using specialty hybrid paints and primers will offer superior, long-lasting results.
Step-by-Step Process for Painting Oils Over Latex
If you decide to proceed with painting oil-based paints over an existing latex finish, follow these steps closely:
- Oil-based paints
- Paint brush, roller, and tray
- 120-220 grit sandpaper
- Clean cloths and paint thinner/mineral spirits for cleanup
- Oil-based primer, adhesion promoter, or alkyd-latex blend paint
- Allow latex paint to cure for at least 2-3 weeks before topcoating. Test a finger drag across the surface—it should feel completely dry and hard.
- Lightly sand the entire latex surface to degloss it using 120-220 grit paper. Don’t sand down to bare paint or you may reduce adhesion.
- Wipe away all sanding dust with a damp cloth. Allow surface to dry again fully.
- Apply an oil-based primer like Kilz or a waterborne alkyd primer. Follow the manufacturer’s instructions for proper application over latex.
- If desired, brush on a layer of clear adhesion promoter. This adds extra gripping power.
- Once the primer has cured per the manufacturer’s directions, apply the oil-based paint using a brush, roller, or sprayer.
- Allow the new oil paint to cure for at least 48 hours before use. Avoid washing or heavy abrading for several weeks to reach full hardness.
- Monitor for cracking or peeling of the new oil paint layer. Immediately repaint any failing areas to prevent spreading.
Ensure the latex paint is fully cured and deglossed before applying oil paints and primers. But even with great care, results may still be mixed. Next we’ll cover troubleshooting tips.
Troubleshooting Oil Paint Problems Over Latex
Painting oil over latex brings inherent risks. But if problems develop, all hope is not lost. Here are some troubleshooting tips:
Issue: New oil paint quickly cracks or peels from latex undercoat
- Solution: The latex likely didn’t fully cure. Thoroughly remove failing paint and allow latex to cure for several more weeks before repainting.
Issue: New oil paint develops spiderweb cracking pattern
- Solution: The layers have incompatible flexibility. Consider stripping paint and refinishing with latex or a hybrid.
Issue: Paint drips or doesn’t level out nicely
- Solution: Humidity may be preventing proper film formation. Dehumidify interior spaces before repainting.
Issue: New oil paint exhibits low or uneven sheen
- Solution: Always use the same brand of paint for primer and topcoat. Mismatched brands often don’t play well together.
Issue: Paint has spots of poor adhesion and delamination
- Solution: Ensure surface was properly deglossed before painting. Spot prime any failing areas before respraying coats.
With proper troubleshooting and persistence, even finicky paint jobs can be salvaged. Don’t expect oil over latex to be as durable as more compatible paint systems.
FAQs About Painting Oil Over Latex
Let’s answer some frequently asked questions about applying oil-based paints to latex:
Q: Can you paint oil-based enamel over latex paint?
A: This is risky but can work if the latex is fully cured, deglossed, and primed with an oil-based primer first. Enamel is very rigid when dry, making the flexibility mismatch with latex even worse.
Q: How long do you have to wait before painting oil based over latex?
A: Wait a minimum of 2-3 weeks for latex to fully cure before applying an oil-based product over the top. Longer is better.
Q: What kind of primer should I use before painting oil based over latex?
A: An oil-based primer like Kilz or a waterborne alkyd primer provides the best results. They prevent delamination between the layers.
Q: Should I sand before painting oil-based over latex paint?
A: Lightly sanding with 120-220 grit paper to degloss before priming is a must. This promotes better mechanical adhesion.
Q: Can I use a latex primer under oil paint?
A: Avoid latex primers under oils. The flexibility mismatch will likely cause poor bonding and premature failure of the finish.
The Bottom Line
Painting oil over latex often creates adhesion problems down the road. For best results, stick to painting latex over cured oil-based paints or primers. Or opt for complete paint removal before switching formulas.
If you must apply oils over existing latex, take steps to thoroughly degloss and prime the latex first. Test for proper adhesion before committing to painting the entire surface. Be prepared to possibly re-do the paint job if cracking or peeling occurs.
With careful prep work and the right primers, oil over latex can work temporarily in low-traffic areas. But the longevity simply can’t match that of more compatible paint combinations. Whenever possible, avoid painting rigid oil paints directly onto flexible latex for a finish that will go the distance.