How To Paint Over Oil-based Paint To Finish A Surface
If you’re planning a paint project, proper planning before you start painting helps you complete the job faster and with less frustration. With that in mind, proper planning encompasses multiple considerations, including selecting the right colors, choosing the right materials, getting the necessary supplies and preparing surfaces for a fresh coat of paint. By taking this time up front, you help ensure your painted surface turns out exactly as you envision.
When it comes to choosing the right materials, different types of paint require different types of supplies and techniques. The main paints used in DIY projects include latex paint, oil-based paint, acrylic paint, alkyd paint and water-based paints like our own Real Milk Paint. If your wood surface has an old oil-based paint on it, however, you can’t simply paint over it with other types of paint without some serious preparation of the previously painted surface.
Why Applying Latex Paint Directly to Oil Paint Is a Bad Idea
Applying latex paint over oil-based paint isn’t recommended for several reasons. The main reason is that latex paint and oil-based paint have different chemical compositions that don’t adhere to each other properly. This incompatibility when you paint latex over oil can lead to flaking, peeling and chipping of the paint job, which spoils the look and functionality of your DIY project.
Another reason applying latex paint over oil-based paint isn’t recommended is due to the difficulty of removing latex paint over oil paint once all the paint dries. And even when you put in the elbow grease, the tedious, time-consuming process of removing layers from the painted surface may not even remove latex paint without damaging the oil-based paint underneath.
If you must apply high-quality latex paint over oil paint, it’s best to do so with a latex primer designed for use with both latex paint and oil paint. Using a paint primer can help ensure that latex and oil paint adhere to each other properly and create a lasting, durable finish.
How to Test Surfaces for Latex Paint or Oil-Based Paint
If you’re thinking of using Real Milk Paint in your projects, keep in mind that this water-based paint doesn’t stick to an oil-painted surface. Minwax stains, varnish, enamels and polyurethanes all contain similar ingredients to oil-based paints, and this is why you need to know the difference between oil-based paint and latex paint before starting your project.
First, it helps to recognize the differences between latex paint and oil-based paint. The most obvious difference is that latex paint is water-based paint, while oil paint has a petroleum base. This difference in mediums means you should examine the instructions for the recommended cleanup procedure. If the container says you can clean up with just soap and water, it’s likely latex paint, but if the instructions say you need mineral spirits, naphtha or paint thinner for cleanup, you’re likely dealing with an oil-based paint.
Drying Time Differences Between Oil Paint and Latex Paint
Latex paint also dries much faster than oil-based paint, which can be a plus or a minus depending on your project. If you’re painting a large surface, you probably want oil-based paint due to its longer open time, or the amount of time you can work with it before the paint dries. However, if you’re doing a smaller project and need to get it done quickly, water-based paint like milk paint or latex paint may be the better choice since the paint dry times are faster.
Steps to Painting Over Oil-Based Paint
Painting over oil-based paint using milk paint or latex requires some hard work, but if you complete the paint job correctly, you can achieve extremely satisfying results.
Ready Your Materials
One of the most important things you can do to ensure a successful outcome when painting is making sure you have all the materials you need on hand before you start. This includes not only your oil paints, latex paint or milk paint but also oil-based primer, painter’s tape, paint roller, plenty of paintbrushes, drop cloths, fine-grit sandpaper and any other tools or supplies you might need. By having everything organized and ready to go before you begin, you can avoid potential delays and disruptions that could set you back or even spoil your project entirely.
Cleaning Your Project Piece
Before beginning any restoration project, cleaning the piece you’re refinishing is a must. The best way to remove layers of old dirt and grime so you can better see what you’re working with is with Tri-Sodium Phosphate cleaner, which is much better than using the usual denatured alcohol. Designed to provide a deep clean on porous surfaces like wood, Tri-Sodium Phosphate readies pieces for restoration and is also a must for cleaning sanded areas before you apply latex paint or milk paint. You can either mix a TSP solution or purchase Tri-Sodium Phosphate cleaner from the Real Milk Paint Co. if you want a premixed option.
Remove Old, Peeling Paint
If the furniture, walls, floor or surface you want to paint has old and peeling paint, it’s important to remove it before applying a new layer. Not only does this help the new paint and oil-based primer adhere better, it also improves the overall appearance of your project. To remove old, peeling paint, you need a putty knife, a wire brush and some serious elbow grease.
First, use the putty knife to scrape off as much of the old oil or latex-based paint as possible. Then, use the wire brush to remove any loose paint chips or debris. Once you’ve removed all the paint, clean up all the old paint from your tack cloth and around your work area, then go on to the next step.
Sand the Surface
The next step to painting latex over older oil-based paint after cleaning off the peeling oil-based paint or oil-based primer is sanding the surface. This requires you to lightly sand the painted surface, then clean up the dust before you paint latex over the surface.
Sanding is an important step in the surface preparation process because it gives the paint a rougher surface to grip onto and fixes surface imperfections. This improved adherence ensures the final paint project looks more even and consistent.
To sand properly, use medium-grit sandpaper and work in long, even strokes in the same direction as the grain of the wood. Once you’ve finished sanding, wipe away any dust with a clean cloth before applying an extreme bonding primer like Ultra Bond Adhesion Promoter by the Real Milk Paint Co.
Painting Over Oil-Based Paint Without Sanding
You can paint older oil-based paint without sanding, but it’s not always the best idea. If the oil-based primer or paint is in good condition, you may be able to get away with just painting over it. However, if the paint is starting to chip or peel, you need to sand it down before painting over it. Otherwise, the new paint doesn’t adhere properly and eventually starts peeling as well.
Special Lead Paint Removal Considerations
Keep in mind that if you’re reading this because you want to paint over older oil-based paint, you may be dealing with lead paint. Older oil-painted surfaces often include lead paint — if not in the top layer, then in the layers beneath. Due to its potential for harm, special measures must be taken to remove the lead paint before continuing. A safe, effective and easy way to do this is by using a product often used by professional painters: our Soy Gel Professional Paint Remover. This paint remover removes old paint easily, encapsulating the original paint for easy cleanup.
Apply a Barrier Coat
To make water-based paint like milk paint or latex paint stick to oil-painted surfaces, you need a barrier coat that acts as a primer. A barrier coat is a coat of finish between the latex paint or milk paint and the oil finish. Before application of this barrier coat, deep clean the surface with TSP (Tri-Sodium Phosphate) to remove any silicones or waxes, then scuff sand the piece for good mechanical adhesion.
For barrier coats, we recommend three products: Ultra-Bond mixed with the first coat of latex paint or milk paint, Zinsser Bulls Eye 1-2-3 water-based primer and sealer or dewaxed shellac. Keep in mind that each barrier coat gives different results.
Extreme Bonding Primer Barrier Coats
With the first method, mix Ultra-Bond with liquid Real Milk Paint or latex for the first coat at a 25% Ultra-Bond to 75% liquid paint ratio. Successive coats can be painted with unadulterated liquid paint, but you want the first layer to adhere well and double as a primer for your piece.
Also, understand that Real Milk Paint does stick well to latex paint that’s cured for 30 days. If the latex isn’t fully cured, you can expect the surface to crack, which can work out well if you want a distressed crackle finish for your furnishings. If not, be sure to wait the full 30 days to preserve the look of your paint job.
Dewaxed Shellac Barrier Coats
Real Milk Paint also adheres to dewaxed shellac, which is generally only available from mail-order companies — shellac available at the hardware store usually has wax. As with uncured latex paint, milk paint cracks and slightly flakes when applied over waxy shellac. And again, if you like a distressed finish, this pairing can provide a nice antique over-painted look.
Zinsser Bulls Eye 1-2-2 Sealer Barrier Coats
Zinsser Bulls Eye 1-2-3 Sealer water-based primer also has titanium dioxide (pigment) and calcium carbonate. This means you can tint the hue to match the shade of the milk paint you plan to use. Tinting is better than just painting over white for darker colors of Real Milk Paint because it improves the opacity of the shade so you need less milk paint for a deep finish.
Once you’ve painted the surface with Bulls Eye 1-2-3 and it’s dried, start painting with your color choice of Real Milk Paint. This procedure likely works best for old plaster walls or surfaces that have seen multiple unknown uses. Zinsser Bulls Eye 1-2-3 water-based primer/sealer is also very good at sealing out silicones and unknown contaminants. (We used this exact procedure in our 1892 house with horsehair plaster walls. — Dwayne, Founder/CEO)
At the end of the day, the decision of how to paint over oil-based paint depends on how much effort you want to put into the project. No matter which option you decide on, the Real Milk Paint Co. has non-volatile organic compounds (VOC) and high-quality products that help you clean, prepare, paint and finish a variety of personal and professional projects.