Nothing beats the fine, shiny finish that polyurethane gives to any surface, be it tabletop, floor top, or your jazzy guitar. The only problem with polyurethane is how it starts to yellow.
While that might be an unavoidable stain, there are a few ways you would keep the polyurethane from yellowing too much.
Does polyurethane yellow?
Polyurethane on any surface turns yellow over time. Primarily the yellow tint occurs due to exposure to UV light. However, oil-based polyurethane becomes a lot more yellow than water-based polyurethane. Applying thin layers and sanding can effectively reduce the yellow tint on surfaces.
Polyurethane is a durable finish to use on chalk paint but the yellowness of the surface will be more noticeable over time. In some cases, if the coatings are too thick and sanding is not effective, the color might even turn orange-like.
Since guitar usually has a wood finish, polyurethane on guitar surfaces fair well since the yellowish hue is not too visible. Yet, on lighter wood colors, you might still notice the yellow stain of an oxidized polyurethane surface.
Polyurethane is not recommended to use on white paint if you want to avoid the yellow stain that would appear over time.
With oil-based poly, the yellowing on white paint would be too visible. Using sanding with water-based poly could diminish the yellow effect to a certain degree.
Since polyurethane dries in a way that gives off a yellow tint, using it over wood is a good idea.
If oil-based polyurethane is used on wood, the yellow tint is not as noticeable. Water-based poly on darker wood practically eliminates any yellow look from the surface.
Making wood wet makes the yellow look less eminent if you’re using oil-based poly.
Why does polyurethane turn yellow?
The primary reason why polyurethane turns yellow over time is sunlight entering your home.
Polyurethane surfaces are subjected to sunlight for long periods, whether directly or indirectly. The UV in the sun’s rays reacts with aromatic isocyanates in the process to produce what we see as a yellow hue.
Moreover, polyurethane itself is a polymer that is prone to get oxidized quite easily. With amines present and UV light coming from all sides, the oxidization process often leads to yellowing of the polyurethane surface.
When polyurethane yellows due to sunlight, the process is usually slower and it would be some time before you notice the color change.
Other than sunlight, what kind of polyurethane you are using contributes majorly to the yellowing. This means that the yellowing on polyurethane would be much worse if the polyurethane is oil-based.
Water-based polyurethane yellows as well, but it takes much longer and the yellowing is a lot more subtle and less noticeable.
Does polyurethane yellow over time?
Unfortunately, polyurethane will yellow over time. Nevertheless, the rate at which it yellows and how fast you notice the stain might depend on a few factors.
One of them is what kind of polyurethane you have on your surface. If it’s oil-based, it is guaranteed to yellow a lot faster than a water-based polyurethane. For oil-based polyurethane, the yellow is also more perceptible.
Moreover, the quality of polyurethane also affects how long it takes a polyurethane surface to turn yellow. Cheaper polyurethane, even if it might be waster based would be more vulnerable to oxidation and eventual yellowing.
Lastly, if the polyurethane surface is exposed to longer hours of direct sunlight, the yellowing is a lot faster.
Does polyurethane yellow in the sun?
One of the prime reasons why polyurethane always yellows is UV light coming from the sun. When exposed to the sun outdoors, poly surfaces yellow rapidly.
If the surface is directly under the sunlight, it might even turn orangish. This happens because of the oxidation reaction that goes on in the polymer and light combination.
Is there a polyurethane that doesn’t yellow?
No, polyurethane will get yellow over time. If you’re looking for polyurethane where you might not notice the yellow tint much, you might want to consider choosing a water-based one instead of an oil-based one.
Since oil-based polyurethane already has a yellow shade to it, the color might even turn more orange eventually, particularly if exposed to UV light.
Few brands yellow the least, and on darker surfaces, the yellow hue might almost escape the eye. These brands include LobaWs 2k supra, Bona Traffic HD, and street shoe to name the few best ones.
All the brands mentioned produce polyurethane that yellows the least. These polyurethanes are all water-based and their durability is also guaranteed.
Does Minwax polyurethane yellow?
Minwax polyurethane is a great quality poly that yellows by the least. Here are the different types of polyurethane:
Minwax Fast-Drying polyurethane:
Minwax fast-drying polyurethane is one of the most durable protective finishes for your wood surfaces and is guaranteed to last a long time.
However, this is still an oil-based polyurethane.
Any oil-based polyurethane will yellow in the long run. With a drying time of 4 to 6 hours, this quick setting polyurethane would yellow less without sanding between the coating layers.
Minwax spray polyurethane:
Unlike the fast drying one, Minwax spray polyurethane is a water-based product.
It might require about a day to dry completely but when it sets, the finish is quite clear. This polyurethane hardly turns yellow for a good period.
Minwax Oil Modified polyurethane:
Minwax oil-modified polyurethane is a composite of both oil and water. That is precisely why the degree of how yellow it gets is somewhat between oil and water-based poly.
Minwax oil-modified poly shows yellow shades slightly more than Minwax spray and less than fast-drying poly.
Does Varathane water-based polyurethane yellow?
Since Varathane is a water-based poly, it does not yellow too noticeably. Generally, Varathane promises the highest level of clarity and to some extent, it also delivers.
To make sure that the polyurethane does not yellow or scratch, it is recommended that Varathane water-based poly is applied in 4 coats.
How to keep polyurethane from yellowing?
The following tips might help you keep your polyurethane surface from yellowing too soon:
Use water-based polyurethane:
The first step to keep polyurethane from yellowing is using water-based polyurethane. Using oil-based or even oil-water mixed poly could result in yellowish hues almost immediately.
Thin layers only:
Even if you are using water-based polyurethane, thick layers of it could be your enemy. The trick to getting a clear finish and minimizing the effect of that sunny yellow shade is by using very thin layers only.
If you wish to keep polyurethane from yellowing, there is no better method than sanding. If you are layering up on the surface, make sure you effectively sand after each coating of poly. When you have sanded, it is equally important to clear efficiently.
Use a primer:
If you are planning on using poly on a white surface, you can use a primer over it. White enamel or milk pain will only help slow down the yellowing process. You must give the primer enough time to dry overnight.
How do you get rid of yellow from Polycrylic?
Here is how you can try to get rid of the yellow from polyacrylic:
Make a mixture:
Make a mixture of 1-part white vinegar and 10 parts water. You can use a spray bottle for this dilute water-vinegar solution. Next, spray the mixture on the surface and use a clean cloth to wipe the surface dry.
Sand the surface:
To get rid of yellow from polyacrylic, you can try sanding the surface. Sandpaper works wonder to remove the yellowish hue. After sanding, take time to clean off the surface well.
Can you use polyurethane on a guitar? How many coats of polyurethane should I put on my guitar?
You can certainly use a polyurethane finish on guitar for a durable and shiny surface look. The poly finish will be water-resistant, as well as scratch-resistant without worry.
Usually, 3 or 4 coatings of polyurethane make sure that that surface is durable. With proper sanding, it would also mean that the poly surface will not yellow too quickly.
Yet, we do need to warn you about the fact that light-colored or white-painted guitars will still look yellow over time when coated with polyurethane. Wooden surfaces would not reflect the yellow color as much.
It is best to use complete water-based polyurethane along with sanding and a few coats to make sure that the yellow effect is curtailed.
Oil-based polyurethane will stain more yellow than water-based polyurethane. Yet, if you use great quality poly in thin coatings along with sanding, the yellow effect might be minimized. The main reason why polyurethane turns yellow is the contact reaction with sunlight.