Polyurethane can help to seal wood and other items for a long-lasting finish. Many ask whether you can use polyurethane over paint as it’s usually used over wood. As a type of plastic, polyurethane can make many items more durable from abrasion, the elements, and temperature. Let’s find out all the relevant information to help you decide if you can put polyurethane over paint.
Polyurethane Over Paint
Polyurethane can, in fact, go over a painted surface to protect the paint and make it last much longer. As a highly resistant barrier, polyurethane can protect painted surfaces from rain, dirt, mold, sunlight, and so much more. While paint offers some protection, especially the high gloss paints, polyurethane protects even better.
However, some oil-based paints may turn yellowish in color over time when they are sealed with polyurethane. For this reason, it’s recommended to use water-based paint if you plan to use polyurethane on top. Keep in mind the only purpose of polyurethane is to protect surfaces for durability.
Process of Applying Polyurethane Over Paint
Before starting any project, you need to prep, and the same goes for applying polyurethane over paint. Keep in mind that the paint should be both dry and fully cured before applying the polyurethane. Paint can take up to a full week to fully dry, and it’s best to wait for a full seven days before applying the polyurethane.
- Cleaning detergent or trisodium phosphate (TSP)
- Lint-free cloths
- 120 Grit sandpaper or 220 grit
- Brush, roller, or sprayer
- Eye protection
How To Apply Polyurethane Over Paint
- Pick your polyurethane. You have the choice of either water-based or oil-based polyurethane. The main difference between the two is the tint and the VOCs. Oil-based polyurethane includes a slight amber tint, has a very strong smell, and dries slower than its counterpart. However, it lasts longer and protects better, especially for items that will be used outside.
- Before doing anything else, you must make sure the painted surface you wish to apply polyurethane to is completely clean and dry. Make sure to remove dust, dirt, mud, and anything else first. We recommend using a soft sponge or a clean rag and a strong cleaning detergent to clean the painted surface. You can use trisodium phosphate mixed with warm water to clean the surface effectively, as it can help the polyurethane adhere to the painted surface by de-glossing while cleaning.
- Now that the surface is clean, it’s time to sand the painted surface to ensure it’s level and in pristine condition for sealer. Use 120 or fine-grit sandpaper to scratch the surface to flatten the gloss or sheen so the polyurethane can stick to the surface. Keep in mind that large or deep scratches will show under the polyurethane. You can do this step by hand or with a palm sander but not an electric sander as it may remove too much paint. Of course, once done sanding, you will need to clean the surface again by wiping away the dust with a damp cloth and allowing it to dry again.
Option: If you want a truly stellar finish, you can add a few drops of your paint to the polyurethane to ensure a strong finish. This step, while not necessary, can prevent a cloudy finish. It does work best with darker paints. Make sure the paint and the polyurethane match, though, as in use oil-based for both or water-based for both. Do not mix oil and water; if you choose to use opposites, then skip this step.
- Now, you are ready to apply the polyurethane of your choice. Use a brush or a spray instead of a roller as it can leave tiny bubbles that will ruin the finish. Do not thin the spray if you plan to use a spray-on application, as it can cause the polyurethane to run and ruin the finish. Apply the first coat using the tool of your choice, and then allow the coat to dry for the time recommended on the product label.
- Once the polyurethane has completely dried, scuff the surface with your 120-grit sandpaper again to remove dust and to flatten any emerging bubbles. The drying time can vary depending on the amount of polyurethane used, size of the surface, and the elements.
- Apply a second coat, and then you are done once it’s fully dried. Allow the piece to cure for a few days or a week before using it to protect the finish. You should not need more then two coats; however, apply two coats for the best protection. Do not scuff the surface with the 120 grit sandpaper, as this will remove the final gloss and then require another coat.
- As with all projects, do not forget to clean up. Use proper ventilation and keep detergent on hand to clean up messes. Soap and water will work for water-based poly. Clean the brushes too with soap and water or mineral spirits.
Paint Drying Time
Paint can take up to 72 hours to dry but can take as little as one day. Several factors can change the drying time, like the weather, thickness of paint, and the size of the object painted. Curing is where the paint is dry and slightly hardened, making it a better surface for sanding and painting. If you are unsure whether the paint has hardened enough to be cured, then give the item a couple more days before applying the polyurethane.
Do not apply polyurethane before the item has finished drying and curing, as the paint can shift and ruin the final outcome. Furthermore, cleaning the item when the paint is not set can further complicate the process and ruin the piece. Once you start to sand the item, you will know beyond a shadow of a doubt whether the item is dry and cured.
Types of Paint
- Oil-Based – can harden a little easier, but they have a strong scent but are extremely durable and great for outdoor use or high traffic areas. Additionally, oil paints take much longer to dry and can be more difficult to clean.
- Water-Based – are more common and environmentally friendly with far less scent. They also dry faster and retain their colors but may not last as long as oil-based paint.
- Chalk-Paint – offers an extremely matte finish but does not require near as much prep work as oil or water-based paints. As long as a surface is clean, dry, and flat it can go over it, even metal or painted surfaces, without sanding or prepping. It’s technically water-based paint with a very low odor.
- Matte or Flat gloss finishes are difficult to clean but have no reflection and need fewer coats.
- Eggshell provides a low gloss that are slightly easier to clean and work for low traffic.
- Satin paint is the most versatile as it can be used inside or outside and in high-traffic areas with a light sheen.
- Semi-Gloss is more reflective and resistant to moisture, making it perfect for high-traffic areas.
- High Gloss is extremely reflective and perfect for high traffic areas as it’s easy to clean.
Types of Polyurethane
Polyurethane, like paint, comes in either water or oil base. Again, the water-based poly requires more applications in the future and is not as durable. However, it does not include strong odors and dries quickly. The oil-based counterpart takes longer to dry but is far more durable and may give a yellow tint. Between the two types, you can use polyurethane over almost any surface so long as it’s clean and dry.
Drying Time of Polyurethane
The drying time can change with many different factors, but it’s extremely important to the finished product. First, check the paint to ensure it’s fully dry but touching an out of sight area. If it’s not sticky or tacky, then it’s dry. Next, find out if the paint is cured by using a fingernail on the paint. Nails will leave an indent if the paint is not cured but will not leave an indent if cured.
Many factors affect drying time, including temperature, humidity, ventilation where painting, the type of paint, poly, and surface you are painting. Read the labels of every product and follow the drying time instructions to get the best finish possible.
As a general rule, you can expect polyurethane to take a minimum of 24 hours to dry. However, wait a full three days to fully cure and be ready for use. Always test the poly using the fingernail test before using the painted and finished item. Oil-based poly can dry to the touch in as little as six hours, but it can take a full week to cure before using the item.
How many coats of polyurethane should I put over paint?
Two coats of polyurethane should be sufficient. While you can add more layers, it may make the clear coat milky in appearance and makes for a lot of unnecessary work. For high traffic areas like a floor or coffee table, you may want up to four or five coats for a smooth finish, especially with water-based poly.
Do I need to apply polyurethane over paint?
No, you do not need to, but it adds an extra layer or two of protection that you may want. Paint can chip, peel, get dirty, and fade. Furthermore, matte and semi-gloss can get very dirty but do not clean well. Many people choose to add this extra protection to prevent additional work down the road. The polyurethane is much easier to keep clean and can keep the piece from warping too.
Does polyurethane stick to all surfaces?
Maybe not all, but polyurethane does stick to many surfaces as long as they are properly prepared. Before applying, the surface needs to be clean, free of dust, wax, grease, and completely dry. Polyurethane is so versatile you can use it over spray paint, latex paint, high gloss paint, and much more. However, you should not use polyurethane over shellac as it’s already a finish.
Can I use polyurethane over chalk paint?
While most people use wax on chalk paint, the wax will need reapplication every year or so. Polyurethane will not require extra application in the future and works perfectly over chalk paint. Do keep in mind that water-based polyurethane works best over chalk paint if you want to avoid the yellowish tint. You can even apply the poly over the wax if you are not satisfied with the wax alone and want a higher sheen. Do wipe the wax down with some mineral spirits or TSP first to make it ready.
Can polyurethane go over acrylic paint?
Yes, you can use the quick-drying acrylic paint and then apply poly over the surface. However, you should use oil-based primer and paint followed with an oil-based polyurethane. As acrylic dries so quickly, it’s often not smooth, but poly can help to even out the texture while adding shine to the matte paint. The process for applying polyurethane over acrylic paint is the same, although you will not have to worry about setting apart so much time for drying.
Should I use polyurethane over white paints or finishes?
You can absolutely use polyurethane over white paint; however, you will want to use water-based poly as the oil-based poly can leave a yellowish tint. If you are looking for an antiqued look, this may work but will not leave the prettiest finish. Although over time, even water-based polyurethane will yellow on a light finish, so you may want to use wax instead.
How can I get a glass-like finish using polyurethane?
After following the steps above for application, use very fine higher grit sandpaper like 600 grit and work your way up to higher grits. Sand lightly and avoid the edges to keep the finish intact. You might need to go to an automotive shop for finer grits than you can find at the hardware store. After, buff with paste wax using a foam sponge or lint-free cloth.
Polyurethane makes a fabulous finish over paint and adds durability and protection. Furthermore, poly can improve the aesthetics of the piece while making it ready to take on the elements. While not necessary, polyurethane can greatly improve any items so long as you follow the proper steps. Happy painting!