When decorating and painting, you want to have the best possible finish when you’re all done. However, not everyone knows how paints and finishes interact, such as whether you can put polyurethane over paint. Can you?
You can put polyurethane over paint and it’s one of the best finishers available. Applied properly, a coat or two of polyurethane varnish will create a thick, shiny coat of protection for your freshly painted surface. Different types of polyurethane are available for differing needs.
What Is Polyurethane?
Polyurethane is a varnish, which is basically a resin solution you apply to wood or metal to give it a hard, shiny, and clear protective coat. Varnish is very useful to ‘lock in’ the look of a fresh coat of paint and create a permanent fixture.
Many wooden floors are coated with varnish to preserve their surface from friction-based wear, as are furniture pieces – especially antiques. Varnish is one of the best ways to preserve antique items or furniture.
Different types of polyurethane varnish exist for differing needs or preferences.
Oil-Based vs. Water-Based Polyurethane
Oil or solvent-based polyurethane varnishes are available and commonly used to finish wood floors or furniture. Water-based varnishes are also becoming common, but the two types have their tradeoffs that you need to consider before deciding which to use.
Oil-Based Pros and Cons
Pros
- Leaves an amber tint when applied
- Requires as little as 2 coats to finish
- Typically cheaper than water-based
- Withstands heat better than water-based
- 50% of its weight is solid, which provides very high durability
- Can last as long as 10 years
Cons
- Very strong odor from toxic, flammable chemicals
- Requires equally toxic chemicals to clean up
- Requires significantly longer to finish compared to water-based
- Amber glow may be undesirable depending on the natural color of the wood
Water-Based Pros and Cons
Pros
- Dries faster than oil-based (2 hours vs 5 hours) so you can do more coats in a day
- Leaves a clearer coat than oil-based, which is perfect for a natural look
- Easily cleaned with water
Cons
- Typically more expensive than oil-based (up to twice the price)
- Needs to be redone every 2 years vs. oil-based’s 10 years
- More likely to crack from heat and UV rays
- Clear look might make some surfaces look ‘cold’
Polyurethane Sheen Levels
It’s worth considering how shiny or lustrous you want your end results to be, whether it’s understated or a high degree of shine. Different types of polyurethane have different levels of shine or sheen, so you need to know the differences between them to get the right product for the job.
Different luster types of polyurethane include:
- High-gloss polyurethane is the shiniest and most lustrous type available. It’s great at highlighting pieces, but also magnifies flaws and imperfections.
- Matte or flat polyurethane is just the opposite, preserving and protecting the surface without calling attention to the varnish coating.
- Semi-gloss and gloss are a medium option that provides a moderate luster in between the first two options.
- Satin polyurethane has low reflectivity but helps to protect against minor scuffs and scratches.
Can You Put Polyurethane Over Paint?
Polyurethane will enhance the color of the paint, plus it adds a protective coat that resists scratches, scuffs, and other wear. Scratches are almost inevitable, especially with oil-based polyurethane, but most good polyurethane varnishes will help prevent the worst of it.
Do You Need Paint To Apply Polyurethane?
You can use polyurethane varnish on natural wood with equally great results, so you don’t need to apply paint. Maple wood has a great natural color that benefits greatly from clear water-based polyurethane varnish, while many people opt for oil-based varnish with other woods, such as oak. It’s ultimately up to personal preference whether they enjoy the amber tint oil-based varnish gives.
Just as with using varnish on paint, it helps to scuff the surface of the floor with fine, 120-grit sandpaper. This gives the varnish a better chance of evenly applying across the entire surface
What Does Polyurethane Work On?
Polyurethane varnish is mainly used on wood surfaces because of its ability to preserve either painted wood or natural wood’s color without harming it. However, many people don’t know that polyurethane can also be used on a variety of other material types.
Some of these materials are:
- Metal
- Plastic
How To Apply Polyurethane Over Paint
Applying polyurethane as a varnish or clear coat isn’t complicated, and the benefits are obvious – a shiny, protective layer that highlights the surface.
Applying the material can be a bit time-consuming, but the efforts are well worth it in the end result.
1. Choose the Right Polyurethane
This depends heavily on what you’re looking for in your end result. If you just want temporary protection with low shininess, a flat or matte water-based polyurethane may be for you. On the other hand, a high-gloss oil-based polyurethane would protect and enhance a hard oak floor. No matter the needs, there’s a form of polyurethane out there ready to meet them.
2. Sand, Sand, Sand!
Use fine 120-grit sandpaper to scuff the surface where you want to apply polyurethane. The main purpose of this is to remove any kind of pre-existing finish such as varnish. If the wood is newer, it may benefit from some rough sanding with 80-grit sandpaper. Once the surface has been sanded, sanding again with finer 180-grit sandpaper can help remove stuck sand particles and other flaws.
Once sanding is satisfactory, blow it off and ensure that your surface is free of sand or dust. Now it’s ready for the first coat of polyurethane!
As a side note, it’s technically possible to apply polyurethane and other finishes without sanding, but you’ll get the best results if you sand the surface beforehand, and they’ll last a lot longer too.
3. Apply the First Coat
Technique and equipment for an application depend on the surface, but the first step is to always stir and not shake polyurethane cans. Shaking introduces air to the mixture, which causes problems with air bubbles in your applications making the coat uneven.
Flat floors call for application with a soft nylon brush or roller, while curved surfaces such as furniture can be coated with a rag dipped in polyurethane. Trying to brush curved surfaces will be more likely to create an uneven and dripping surface.
For those hard-to-reach areas, aerosol polyurethane is a godsend! Simply shake the can and spray 6-12 inches away from the area you’re coating.
4. Sand It Again!
Because nobody is perfect at applying polyurethane, you’ll have some rough spots in your first coat. That’s fine, and you shouldn’t stress about them – that’s why you’re going to sand it again! Uneven and dripping areas of your dry first coat should be sanded down before you put on a second coat. Applying a second coat on top of these rough areas will only highlight the flaws in it.
5. Rinse & Repeat
Water-based polyurethane can call for as many as 4 coats before the surface is really finished, while with oil-based polyurethane you can get away with as few as 2 coats. The most important thing to watch for during the whole process is to be aware of imperfections and be willing to sand them down for another coat.
Polyurethane Alternatives
If polyurethane doesn’t suit your needs for finishing a surface, there are plenty of alternatives available to choose from. Some people don’t like the look of polyurethane varnish, while others opt for other options out of concern for the environment; polyurethane is a synthetic compound. From lacquer, shellac, and more, there are natural products that produce similar results to polyurethane.
Lacquer
Lacquer is a product that uses clear nitrocellulose suspended in a solvent solution. Once dry, lacquer becomes a shiny and clear protective layer. Lacquer as a finishing agent is particularly known for being crystal-clear once dry. This can be useful to preserve a particular color the way it is without changing it with a tint, but isn’t as strong as shellac or polyurethane.
Shellac
Shellac is similar to lacquer but more natural because it doesn’t use solvents. Shellac is used to produce a brilliant sheen and is in fact why Skittles are so shiny! Shellac is available in multiple colors, making it useful to change a surface’s characteristics. The fact that shellac doesn’t use solvents is also a boon to the environmentally conscious. Shellac is harder than lacquer but less durable than polyurethane.
Varnish
Varnish is often used as a catch-all term for finishers, but varnish itself is made of solvents, oil, and alkyd resin. Like lacquer, the solvents evaporate after application, and the layer left behind hardens and becomes water-resistant. Varnish is a little outdated these days but is useful for areas exposed to water, like decks.
Final Thoughts
Polyurethane is a great product to use for finishing and sealing wood, particularly floors and furniture. While there’s a bit of difference between oil and water-based choices, polyurethane is simple to apply yourself with great results that keep paint looking brand-new and fresh.
