Painting over polyurethane: A complete guide

Many wood surfaces in your home or office are coated with polyurethane, which helps protect wood from the effects of frequent use and age. You can find polyurethane on your kitchen cabinets, wood trim, and outdoor deck.

But what was considered stylish decor 20 years ago is probably looking a little dated today.  

Recent trends in contemporary and minimalist home decor have led many homeowners to update their spaces with painted cabinets, stairs, and trim. You can see this often happening in kitchens as people update their wood cabinets with matte, white paint, or more dark, dramatic shades.

As today’s interior designs favor more neutral and matte finishes, people have wisely been using paint to achieve a new look rather than going through the hassle of replacing all their woodwork.

Although these simple decor changes can give a fresh, modern look to your space, there are a few things you should know before jumping in and repainting your old woodwork, especially if it has a coat of polyurethane varnish already applied. 

Spectra Painting Contractors offers professional services for any home or office painting project. Our team of professionals can help you get any painting project done quickly, and we will save you lots of time and trips to the hardware store for supplies. 

What is polyurethane?

Polyurethane is a wood finish that protects against scratches and water damage.

You can use either oil-based or water-based polyurethane to treat woodwork. Oil-based polyurethane adds a warm, amber hue to woodwork and it takes awhile for each coat to dry. Water-based polyurethane dries clear and quickly.

To know if the wood is coated in a water-based or oil-based polyurethane, drip a little water on the wood surface. If the water beads up after a couple of minutes, the coating is oil-based.

Can you paint over polyurethane?

Do not assume that you can use any type of paint you have laying around to cover your polyurethane-coated wood. Since polyurethane is supposed to keep the surface clean and durable, it can be difficult for some types of paint to bind onto a wood surface that has polyurethane. The painting process requires quite a bit of time and elbow grease to get done correctly. 

Here are a few quick things to know about painting over polyurethane:

• Painting over polyurethane will not be a quick project. Expect the process to last at least four to seven days, according to an article in Good Housekeeping.
• If the project gets rushed or a step gets omitted, you could end up with ugly, streaky woodwork. 
• Every polyurethane surface needs to be cleaned, sanded, repaired and primed before the painting can begin. Preparation is pretty lengthy and labor-intensive, but it is vital to get it done correctly for the best possible results. 
• For outdoor jobs, be sure to choose a time when you’ll have at least a few days of hot, dry weather.
• Expect to use at least three coats of paint once the wood is primed and dry.

How to paint over oil-based polyurethane:

A surface coated in oil-based polyurethane always needs to be wiped down with a trisodium phosphate solution and sanded before it can get painted. The trisodium phosphate helps remove any dirt, grime, or stains from the surface.

Sanding the wood will manually remove the polyurethane varnish. You will typically see experts use a sanding sponge, sanding block, or a power sanding tool until the polyurethane finish is completely gone. 

Once the bare wood is exposed, a thin coat of primer is applied. The second coat of primer gets applied once the first coat is dry to the touch. Both coats of primer will need to dry overnight. It is crucial to use the correct primer formula for this step, which will depend on what type of paint you plan to use.

The next day, once the primer coats are dry, the surface gets sanded again to even out the texture and remove any blotches of primer. After that, the wood surface will be ready for the first coat of paint. 

How to paint over water-based polyurethane:

A new coat of paint also won’t adhere to a surface coated in a water-based polyurethane.

The removal process is similar to how you’d remove an oil-based polyurethane.

First, wash the surface with a grease-cutting detergent and let it dry.

Then, sand the surface and clean up the dust. Follow up with an oil-based primer and allow it to dry for 24 hours.

So, while it is possible to paint woodwork with a polyurethane coating, there are quite a few steps to go through before you can get there. 

Painting the woodwork in your home is an important job, and it is best to do it correctly rather than risk making a potentially costly mistake. Paint that’s applied over polyurethane without the correct preparation can look streaky and uneven.

Contact the experts at Spectra Painting Contractors for fast and professional service in the Boston area. We’re experienced at reviving old woodwork in homes and offices, and would be happy to work with you on painting over polyurethane.