When painting, we sometimes want or need to paint over spray paint, but is that even possible? If so, how do we do it so that the project turns out to be a success?
To paint over spray paint, you should assume that the spray paint is oil-based. If you plan to use oil-based paint, then prepare the surface and paint as you normally would. However, if you plan to use water-based paint, then a primer is essential.
Painting over a surface that has been spray-painted is not as difficult as it sounds, and if you are using an oil-based paint, follow the steps you would for any project you are repainting. Although conventional wisdom is that you cannot paint acrylic or latex paint over oil, conventional wisdom is not always right. To learn how to paint over spray paint, read on.
Assume It Is Oil-Based Paint
Although people assume that all spray paint is oil-based, that is not always the case. Most spray paints use an alkyd, oil, or binder, but brands such as Krylon and Rust-Oleum sell acrylic spray paints. However, since most spray paint is oil-based, most sources on the net will say spray paint is oil-based.
Since you can’t be sure of the paint’s exact chemical compounds, assume the spray paint is oil-based. That does not mean you will have to use another oil-based paint. Although the general rule of thumb with paint is “fat over lean” (oil is fat and acrylic is lean), rules are meant to be broken, right? Later we will explain how to paint latex over oil.
If you want to be sure or think there is a chance the spray paint is latex, you can test the paint following these steps:
- Add some soap to warm water and scrub a small area of the painted surface.
- Wipe the soap off and wait for the area to dry.
- Soak a cotton ball in rubbing alcohol and rub it over the area.
- Check if your cotton ball has paint on it.
A clean cotton ball means you are dealing with oil-based paint. If the paint comes off in this test, it is water-based.
Make Sure the Spray Paint Is Dry
In case you used spray paint on the surface recently and want to cover it up, give the spray paint time to completely dry. If the spray paint claims that you can paint a second coat in five minutes, ignore it. The paint needs to be dry enough not to smear when you apply a brush.
Paint goes through several stages on its way to being dry:
- Surface dryness: The surface will have a hardened film in this stage, but the paint underneath the film is still wet.
- Dry to the touch: When you touch the paint, it will feel dry, but if you press down, you will mess up the paint.
- Hardened state: In a hardened state, paint won’t come off on your fingers when you touch it. However, the paint is not completely hard yet, and touching it could leave fingerprints.
- Thorough dryness: You can now move the workpiece. Plan on a minimum of 24 hours for this process.
- Cured: When the paint is cured, enough solvents have evaporated; scrubbing or washing it will not affect the finish. Curing time for oil-based paints can be anywhere from seven days to a month.
Remove Any Loose Paint
If the surface has peeling paint, then remove it. Use wood putty to fill scratches or gouges. Do not forget to feather the edges of the paint to create a smooth seam so that your repair work does not show on the finished product.
For metal surfaces, use a metal filler to fill in any scratches or problems with the surface. The Devcon Metal and Patch Fill is a waterproof formula that builds up worn surfaces and can be painted over. Set time is one hour, and it cures in six, which is about the same time as wood putty.
Sand the Surface
The purpose of sanding a surface for painting over spray paint is not to remove the existing paint. Instead, you want to give the new paint something to stick to, and sanding creates small ridges that the new paint can stick to. Sanding also lets you remove any slight imperfections.
For this project, you probably should use sandpaper in the 180 to 220 range. It will create the small grooves you need to help the new paint stick to the spray paint. Medium or coarse grit paper will remove too much old paint. Grit paper above 220 is for light sanding between coats or when you are working with hard surfaces like metal.
Remember your goal when thinking about how long to sand. It is not to remove every flaw and scratch but to create a surface for the new paint to grip to. If the surface is no longer slick and is level, wipe down the surface with a tack cloth.
Do not forget to sand with the grain if working with wood.
Prime the Surface
To prime or not to prime—it seems that plenty of people have their opinions about priming—and they are not the same. A person’s perspective might be based on their circumstances. For example, painters who charge by the hour might recommend a primer, while the painter who charges by the job might insist that primers are not needed.
A retailer could recommend products based on profit margins, and DIYer might be inclined to listen to those who claim primers are not needed, especially when they have access to self-priming paint.
Instead of focusing on people’s opinions, let’s discuss what primers do:
- Provide a stable base
- Create a surface for the paint to stick to
- Hide imperfections
- Block out stains
- Bring paint color back to a neutral white so that the new paint is true to its color.
Finally, if you are painting latex over oil, you have no choice—you must use a primer first.
The Extra Step You Need When Painting Water-Based Paint Over Oil-Based
After you finish sanding your piece, use a tack cloth to clean sanding dust from the surface. Then you’ll need to do a deep clean using a TSP Trisodium Phosphate heavy duty cleaner. TSP not only cleans dirt and grime, but it also improves adhesion by etching the surface you will paint.
Have a pair of gloves, safety glasses, two buckets of warm water, and two sponges ready.
- Put on your gloves and safety glasses.
- Make a solution of one gallon (3.8 liters) of warm water and ¼ cup of TSP.
- Use a sponge dipped into the TSP solution to clean the surface.
- Rinse the surface with a sponge dipped in clean water.
- Let the surface air-dry. You are ready to prime.
Usually, a single coat of primer does the trick, unless you are painting an extremely light color over a dark color. However, be prepared to use two coats of primer, especially if the original paint color or surface imperfections are visible.
Paint the Surface
Assuming you have prepared the surface, primed it, and the primer is dry, the only thing left for you to do is to paint the surface. Specific directions on how you can go about it depend on your project. Check out our website for posts about particular projects.
Painting over spray paint does not require that you remove it. Sand out any imperfections, remove flaking paint, and assume you are working with an oil-based paint. You will probably want to use a primer if you intend to use water-based paint.