One of the easiest ways of redecorating your home is with a fresh coat of paint. Changing the color of your cabinets, floors, or door and window frames can make a dramatic visual impact. If you are concerned about painting a surface because it has a polyurethane coating, you have come to the right place.
Oil-based paints, like enamel, can be painted directly over polyurethane. The problem with polyurethane is that it is very smooth and, therefore, difficult to form a mechanical bond with the new paint. You should sand or de-gloss polyurethane and use a suitable primer prior to painting it.
Polyurethane finishes are notoriously difficult to repaint because some paints do not stick to it very well and may start to peel off shortly after the new paint has dried. Choosing the right type of paint that will adhere is important when painting a polyurethane-covered surface. There are important steps to follow when you are painting over polyurethane that ensure a proper bond between the paint and the surface.
What Is Polyurethane?
Polyurethane paint is a type of liquid plastic that is applied as a clear topcoat or varnish. When it has dried and cured, it gives a hard, durable finish. Polyurethane is traditionally oil-based, but there are modern water-based polyurethane coatings.
Polyurethane is often used on wooden floors or furniture to prevent scratches and dents. It is also used on surfaces that expand and contract with temperature because it is elastic, like latex paint, when it dries.
The main challenge one faces when painting over polyurethane is that it is glossy, making it difficult for other paint to physically adhere to it.
What Paint to Use for Polyurethane
It is best to paint over polyurethane surfaces using oil-based enamel paint, as this will stick to the polyurethane the best.
One can also use water-based latex or acrylic paint over polyurethane, but you need to first apply a coat of primer that is compatible with water-based and oil-based paints.
Always Sand Before You Paint Polyurethane
Appropriate surface preparation is essential when painting over polyurethane. It is more important than the type of paint you use because both water-based latex or acrylic paint and oil-based enamel paint will stick to polyurethane, provided it has been sanded sufficiently.
Sanding the polyurethane with fine-grade sandpaper creates lots of tiny scratches that help the new paint adhere to the surface without peeling. The goal here is not to remove as much of the polyurethane layer as possible, merely to roughen the surface.
Sanding is often the most time-consuming and tedious part of a DIY paint project, but luckily there are products available to hurry this step along! Liquid sandpaper or deglosser is available at most hardware stores for under $10. It uses chemicals to achieve the same outcome as manually sanding in a fraction of the time.
Sandpaper vs Liquid Sandpaper
While liquid sandpaper sounds like the perfect time-saving solution, there are some instances where it may be better to use good old sandpaper. One should consider the following when deciding between using liquid sandpaper or regular sandpaper:
- Harsh chemicals. Liquid sandpaper contains strong chemicals that penetrate the polyurethane. These give off volatile organic compounds (VOCs), which we can smell as paint fumes. The VOCs are toxic to inhale, so one should always wear a painter’s mask and work in a well-ventilated area. Look for brands of liquid sandpaper that are low in VOCs.
- Cost. Do you already have sheets of regular sandpaper at home? If you are doing a low-budget DIY paint job, it may be better to use what you have available rather than buying a new product. Although liquid sandpaper is not very expensive – one can buy a 32-ounce bottle for around $10 – it can be pricey if the item you want to degloss is very large.
- Size and shape of the item. One benefit of liquid sandpaper is that it can get into nooks and crannies better than traditional sandpaper. If the item you are painting is intricately carved, use liquid sandpaper. If the item is large and flat, consider using sandpaper and an electric sander to make the job go faster.
How to Paint Over Polyurethane
Before you begin your painting project, gather the following supplies:
- Mineral spirits
- Clean, lint-free rag
- Fine grit sandpaper or liquid sandpaper
- Painter’s mask
- Oil-based primer
- Oil-based paint in the color of your choice
- Oil-based topcoat
Once you have everything you need, it is time to begin the project! The following steps need to be followed:
- Start by dampening a rag with mineral spirits and use this to thoroughly clean the entire polyurethane surface.
- Put on your protective face mask, whether you are using liquid sandpaper or regular sandpaper. The VOCs in the liquid sandpaper are toxic, and so is the polyurethane dust created by sanding.
- Use the fine-grit sandpaper to sand the entire surface, removing every bit of shine. Wipe away the dust using a rag and mineral spirits. If you are using liquid sandpaper instead, follow the directions for use on the packaging.
- Paint on a coat of primer and allow it to dry thoroughly. You may need to leave it overnight.
- Apply the colored paint. If more than one coat is necessary, allow the paint to dry properly between coats.
- Apply the first layer of the topcoat.
- Once you have left it to dry overnight, sand it lightly using fine-grit sandpaper and wipe the dust from the surface using a clean rag dampened with mineral spirits.
- Apply the second layer of topcoat and wait a full 72 hours for it to dry and cure to its full hardness.
Best Primers to Use for Polyurethane Surfaces
It can be daunting to choose from the huge variety of primers available at the hardware store. Here are the best brands of primer that have been proven to work well for polyurethane surfaces:
- KILZ Adhesion Interior/Exterior Primer. This oil-based primer is designed for optimal adherence to glossy surfaces like polyurethane. The greatest advantage of this primer is that it is dried fully in only 30 minutes!
- Zinsser Bulls Eye 1-2-3 Primer. This product is designed to be used on a variety of surfaces and can be used with any topcoat. The formulation is water-based, but it is great at sticking to high-gloss surfaces like polyurethane. It inhibits rust and is mold resistant.
- KILZ Low Odor Interior Primer. Other than providing excellent adhesion, the greatest advantage of this primer is that it has much lower VOCs than other oil-based primers. It only takes one hour to dry, making it a great option for low-ventilation areas in the house.
Polyurethane is a highly durable, clear topcoat that is often used on surfaces that experience a lot of wear, such as wooden floors.
The best type of paint that will stick to polyurethane surfaces is oil-based enamel. Latex or acrylic paints cannot be used on polyurethane.
Extra care must be taken to prepare the surface to prevent the paint from peeling. It is vital to clean the surface well with mineral spirits and to thoroughly degloss it, using sandpaper or liquid sandpaper prior to painting with primer. This step is important to help the primer and paint stick to the polyurethane.
There is a range of primers available on the market that are designed to work well on high-gloss surfaces, such as polyurethane. If your painting project is indoors, choose a primer that has low VOCs to avoid inhaling toxic fumes.