Polyurethane is a colorless finish that seals the surfaces underneath it and protects them from water, scratches, and moisture. But, sometimes the sealer turns yellow, so how to fix it?
To fix yellow polyurethane, scrub it with mineral spirits and a soft sponge to remove the yellow tint. You can also scruff the top layer with ulta fine-grit sandpaper to remove it.
In most cases, you can’t fix the yellow polyurethane unless you remove the whole coating and re-apply it.
Why Does Polyurethane Turn Yellow?
Polyurethane turns yellow because of the oils in its formula, because it absorbs oils, tannins, and dye from the material, due to a chemical reaction of its additives, because of over-accumulation of synthetic oils, and UV exposure.
The sealer will absorb oils, tannins, and dye from the material and will change its color due to usage and dust accumulation.
Polyurethane is a durable sealer – its strength is due to its formula that contains different additives, such as resins and plastics. Due time, a chemical reaction between these additives will discolor and yellow the coating.
The finish will also turn yellow because of an over-accumulation of synthetic oils. The oils in the coating will turn the clear coating yellow.
Interior polyurethane will turn yellow if exposed to UV rays (sun). The UV rays will penetrate the coating and increase the heat between layers — this causes the finish to turn yellow or brown.
How To Fix Yellow Polyurethane?
To fix yellow polyurethane do the following things.
- Use Mineral Spirits.
- Use Light To Fade The Yellow Tint.
Note: There’s no quick way to fix a yellow finish because all the coatings are affected, not just the topcoat. So, whatever you use to fix the topcoat must also fix the undercoats.
1. Use Mineral Spirits
Scrub the yellowed polyurethane with mineral spirits and a soft sponge to get rid of the yellow tint. Mineral spirits will dissolve and remove grease or deposits on the coating.
Scuff (or sand off) the top layer to remove most of the tint if the finish is yellowed due to UV exposure. In this case, the top coat is usually the most affected so sanding it can lighten the finish and get rid of it.
2. Use Light To Fade The Yellow Tint
Once oil-based polyurethane starts to dry, an atom named “chromophores” starts to form. This atom gives the sealer a yellow tint if the coating is placed in dark places without UV light.
The yellow tint will start to disappear if you place the coating outside. The coating must be outside for this to happen and not near windows because windows block UV light.
This method won’t prevent the coating from turning yellow as it will happen eventually, but it will slow it down.
Note: Strip the finish and re-apply it if nothing works.
Related Read: How To Fix Sticky Polyurethane?
Does Water-Based Polyurethane Turn Yellow?
Water-based polyurethane rarely turns yellow as it has a low level of VOCs, paint chemicals, and solvents, meaning the coating is less likely to change its color.
Water-based polyurethane can turn yellow if its coating absorbs oils, tannins, and stains from the wood.
Cheap and low-quality water-based polyurethane products tend to change their color over time. However, this takes a while before it happens, usually over 3 years.
How To Prevent Polyurethane from Turning Yellow?
To prevent polyurethane from turning yellow do the following things.
- Ensure the material to be painted is dry.
- Apply a stain-blocking primer like shellac before applying the sealant.
- Use exterior polyurethane because the top coat is designed with UV blockers.
- Use sealants that contain silicone compounds like a rust-oleum sealant.
- You can also try sealing the finish with a coat of UV-resistant sealant.
Can You Paint Over Yellowed Polyurethane?
You can paint over yellowed polyurethane, but you must sand off the glossy layer first and apply a stain-blocking primer.
However, if the polyurethane is yellow it’s best to remove it rather than paint over it. This will produce a better finish and reduce the weight and number of coats underneath it.
If you decide to paint over it, use an exterior sealer as they contain silicone compounds that prevent heat and UV rays from changing the coat color. Rust-Oleum is a good choice.
Related Read: Can You Apply Polyurethane Over Polyurethane?
Which Types of Polyurethane Don’t Turn Yellow?
Water-based polyurethane is known to yellow less as it contains fewer chemicals in the formula, uses water as its solvent, and has no oily deposits that can change the color of the coating.
Water-based polyurethane is also less prone to weathering effects as UV exposure and heat won’t make it change color as it would on oil-based polyurethane.
Here are the brands you should use:
- Bona Traffic HD water-based polyurethane
- Loba WS 2K Supra
- Pallmann’s Pall-X 96.
Will Polyurethane Turn White Paint To Yellow?
Polyurethane will not turn white paint to yellow as it’s a clear coat and doesn’t contain pigments or colorants.
Polyurethane is colorless and designed to reveal the color of the paint underneath it. If you apply it over white paint, the finish will remain white but it will have a glossy layer over it.
However, oil-based polyurethane can make a white paint yellow over time. This is because, once the polyurethane yellows itself, it will also turn the whole finish yellow.
When this happens, it’s not the white paint underneath that changes the color, but the sealer on top.
Since the clear coat is changing its color due to polymer degradation or UV exposure, it can make the white paint underneath change its color too. But, if you remove the sealant, the paint underneath will have the same color.
Related Read: How To Thin Polyurethane?
Does Vrathane Polyurethane Turn Yellow?
Oil-based varathane polyurethane does yellow. However, its water-based type tends to yellow less.
Does Wipe on Poly Yellow Over Time?
All oil-based polyurethane will yellow over time, including wipe-on poly. However, some types tend to last longer before changing their color. So, wipe-on poly takes longer to change its color and remains clear for several years.
How Long Does it Take Oil-based Polyurethane To Turn Yellow?
The time it takes oil-based polyurethane to change its color depends on a lot of factors. The thickness of the coat applied, and how much the coating gets exposed to UV lights, all determine the time it takes the sealant to change its color.
As a rule of thumb, it can take oil-based polyurethane between 6 months and 2 years to develop a yellow tint. On the other hand, water-based poly remains clear for 1-3 years.
However, these are estimated values as the time depends on the factors we mentioned.