You can paint over polyurethane after proper surface preparation. The surface must be cleaned, sanded, and primed for the paint to adhere properly. Choosing the right paint and tools, avoiding common mistakes, and thorough clean-up after the painting is also important for completing the job.
We tested multiple ways of painting over PU in our woodshop and came up with a step-by-step process for getting excellent adhesion when applying paint over polyurethane.
Before painting over polyurethane, prepare the surface properly to ensure that the paint will adhere correctly and the final finish will be smooth and flawless.
Neglecting to do so can result in unsatisfactory results, such as paint peeling, flaking, or chipping.
Therefore, cleaning the surface thoroughly and removing contaminants (mildew, mold, grime, grease, and dust) that may affect the paint’s adhesion is important.
Mineral spirits, liquid sandpaper, or wood cleaners can clean the surface and effectively remove these contaminants.
Sanding the polyurethane-coated surface is an important step in the preparation process.
It not only helps to roughen up the surface, allowing the paint to adhere better, but also removes any glossiness or yellowing caused by the polyurethane coating, resulting in a clean, even finish.
When sanding a polyurethane-coated surface, selecting the right sandpaper grit is important.
For smooth surfaces, use coarse grit sandpaper, such as 80 grit, to create tiny scratches that will provide a better bonding surface for the paint.
If the surface is already textured, use fine-grit sandpaper, such as 120 grit, to avoid creating deep scratches that can be difficult to cover with paint.
In addition to choosing the right sandpaper grit, it’s important to sand the surface evenly and avoid sanding too aggressively, which can damage the underlying wood surface.
Also clean the surface thoroughly after sanding to remove any dust and debris that may interfere with the paint’s adhesion.
Using the right primer is crucial in preparing a polyurethane-coated surface for painting.
A primer acts as a bonding agent between the paint and the surface, allowing the paint to adhere better and last longer.
When painting over polyurethane, use an oil-based primer instead of a latex one.
Oil-based primers are superior for painting over polyurethane because they have excellent adhesion and can soak into the wood to form a seal without raising the grain, which can occur with latex primers.
Although oil-based primers can be messy and have a strong odor, they provide better results and are worth the effort.
On the other hand, using a latex primer could result in a tannin bleed, which is when the tannins in the polyurethane resins bleed through the paint, leaving a yellowish or orangey appearance.
It can ruin a paint job, so using an oil-based primer is important.
After priming the surface, you can use oil, water, latex, or chalk paint over polyurethane.
Oil-based paint is durable but requires mineral spirits for thinning and has a strong odor, while water-based paint is easier to work with and can be cleaned up with soap and water.
Latex-based paint is more flexible than regular water-based paint, and chalk paint has a unique matte finish favored for furniture and decorative projects.
Using the right paint applicator is also crucial for achieving a smooth and even finish.
Natural bristle brushes are recommended for oil-based paint, while synthetic or natural bristle brushes can be used for water-based paint.
Rollers are great for larger areas, and brushes work best for finer details.
A paint sprayer can also be used for a more precise and even application, but it requires some practice.
Once the coat of paint is applied, leave it to dry. It can take anywhere from 8 – 24 hours to dry completely.
Here are some tips to help you achieve the best results when painting over polyurethane:
Applying paint over polyurethane can be challenging, but with the right preparation and technique, it can be done successfully.
One of the most important steps is properly preparing the surface by cleaning it thoroughly and sanding it to remove any old finish.
Applying a primer is also essential for ensuring proper paint adhesion and preventing tannin bleed.
I recommend you use mineral spirits to thin out the stickiness of the oil primer so that it brushes on more smoothly.
Finally, avoid common mistakes like applying too much paint or not waiting long enough between coats.
It’s not recommended to paint over polyurethane without sanding because the surface needs to be roughened to create a surface to which the paint to adhere. Skipping sanding may result in the paint peeling or flaking off.
You don’t necessarily need to remove all polyurethane before painting, but the surface needs to be prepared properly. This includes cleaning, sanding, and priming with an oil-based primer to ensure the paint adheres correctly and achieves a long-lasting finish.
Various types of paint can stick to polyurethane, including oil-based, water-based, latex-based, and chalk paint. However, it’s crucial to properly prepare the surface by cleaning, sanding, and priming with an oil-based primer to ensure the paint adheres correctly and achieves a long-lasting finish.