How to Fix Yellow Polyurethane? (3 Methods)

Polyurethane is a durable finish that lasts very long on the material. But over time, the polyurethane starts to yellow. So how do you fix this?

To fix yellow polyurethane, you can scuff the top layer with ultra fine-grit sandpaper. 220-grit works fine. The sandpaper will help to remove the yellow tint and lighten the polyurethane finish.

However, in most cases, using ultra-fine sandpaper to remove the yellow tint won’t work. So the best way to fix yellow polyurethane is to strip the finish with an alcohol-based solvent or chemical stripper.

Then bleach the wood using Clorox bleach, apply a stain-blocking primer and apply a non-yellowing finish. But, there’s more to this. We explained everything you need to know down below.

Why Does Polyurethane Turn Yellow?

Polyurethane turns yellow for different reasons. But, the most common reasons are the oils in the top coat. Also, polyurethane turns yellow due to chemical reactions in the paint coating, polymer degradation, and UV exposure.

Polyurethane turns yellow as the top coat pulls and absorbs oils, tannins, and dye from the material used on. Polyurethane also turns yellow over time due to usage and dust accumulation. Polyurethane turning yellow is more common with oil-based polyurethane.

Polyurethane is a very strong top coat. The strength of the top coat is due to the paint formula. Polyurethane contains many additives including resins and plastics. Over time, a chemical reaction can occur between these compounds leading to discoloration or yellowing of the polyurethane coating.

The yellowish tint is also caused by an over-accumulation of synthetic oils. Over time, the oils in the polyurethane coating can turn the clear coat yellow.

Another reason for yellowing is due to UV exposure. This mostly affects indoor polyurethane because it doesn’t have UV protection. This causes the UV rays to penetrate the polyurethane coating and increase the heat between the coats. Over time, the over-exposure to UV rays can cause the clear coat to turn yellowish or brown.

Absorbent qualities of the paint thinner or solvent is another reason. This is more common with water-based polyurethane. Water-based paints tend to pull or suck materials from the surface. This is why water-based paints are common for raising wood fibers.

For water-based polyurethane, the solvent can also pull dye and tannins in the wood. If the wood has a lot of oil or stain that wasn’t sealed with a stain-blocking primer, this can turn polyurethane yellow, or sometimes, orange.

How To Fix Yellow Polyurethane?

There is no quick fix to get rid of yellow polyurethane. This is because when polyurethane yellows, it’s not just the top coat that is affected. The undercoat will also be affected. So whatever fix you try or use on the top layer of the polyurethane, it won’t work on the undercoat. So technically, the yellow tint will still be present.

1. Use Mineral Spirits

However, you can scrub the yellowed polyurethane with mineral spirits and a soft sponge. This can help get rid of most of the yellowing. The mineral spirits will dissolve and remove grease or yellow deposits on the polyurethane.

You can also try scuffing the top layer of polyurethane to remove most of the yellow tint. 220-grit sandpaper will work fine. The sandpaper will help to remove most of the yellow tint on the top layer of the polyurethane.

This hack works better for polyurethane that has 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 the yellowing.

2. Use Light To Fade The Yellow Tint

As soon as oil-based polyurethane starts to dry, an atom named “chromophores” start to form. This atom gives the oil-based polyurethane that yellow tint. If the oil-based polyurethane coating is placed in dark places without having access to UV light, this atom will start to give the polyurethane that yellow tint. 

However, if you place the oil-based polyurethane furniture outside, the yellow tint will start to dissapear after a while. The oil-based polyurethane should be outside for this to happen and not near windows because windows block UV light.  However, this won’t prevent oil-based polyurethane to turn yellow, it will happen eventually, but this method will slow it down. 

If nothing works, then the best way to fix yellow polyurethane is to strip the finish with a chemical paint stripper, seal the material with a stain-blocking primer, and apply a fresh coat of non-yellowing sealant.

Related Read: How To Fix Sticky Polyurethane?

Does Water-Based Polyurethane Turn Yellow?

Water-based polyurethane rarely turns yellow over time because it has a very low level of oils in the coating.

Water-based polyurethane has a low level of VOCs, paint chemicals, and solvents which means the paint coating is less likely to turn yellow.

However, water-based polyurethane can yellow over time based on the absorbent qualities of the paint coating. Water-based polyurethane can pull or absorb oils, tannins, and stains from the wood leading to the polyurethane coating turning yellow.

Asides from that, cheap and low-quality water-based polyurethane products are also yellow over time. However, this takes a while before it happens, usually over 3 years.

How to Keep Polyurethane from Yellowing?

The following tips will help to prevent your polyurethane from yellowing:

  • Ensure the material to be painted is dry.
  • Apply a stain-blocking primer like shellac before applying the polyurethane.
  • Use exterior polyurethane because the top coat is designed with UV blockers.
  • Apply non-yellowing polyurethane like water-based polyurethane.
  • Use sealants that contain silicone compounds like rust-oleum sealant.
  • You can also try sealing the polyurethane finish with a coat of UV-resistant sealant.

Can You Paint Over Yellowed Polyurethane?

Can You Paint Over Yellowed Polyurethane

You can paint over yellowed polyurethane. But to do so, you need to sand the polyurethane to remove the top glossy layer first.

You’ll have to seal the yellowed polyurethane with a stain-blocking primer like shellac. After, you should apply a non-yellowing finish on the polyurethane to prevent it from happening again.

However, it’s better not to paint over yellowed polyurethane. If the polyurethane is yellow, it’s time to strip it and apply a new finish. This will produce a better finish and reduce the weight and number of coats on the material underneath.

If you paint over yellow polyurethane, you should use a non-yellowing sealant. These sealants often contain silicone compounds that prevent heat or UV rays from turning the coat yellow. A good choice is a rust oleum finish.

However, if the polyurethane turns yellow, this means it’s time for it to go. If you take the risk and paint over yellowed polyurethane, the whole finish can come off after a while. Especially, if the yellowing is caused by bleed-through.

Related Read: Can You Apply Polyurethane Over Polyurethane?

Types of Polyurethane That Don’t Yellow

Water-based polyurethane is known to yellow less than oil-based polyurethane. This is because there is a lower level of paint chemicals in the polyurethane.

Also, water-based polyurethane has water as its solvent. So there is no oily deposit or residue that can yellow the paint coating.

Water-based polyurethane is also less prone to weathering effects. UV exposure and heat will not make the water-based polyurethane yellow as it would on oil-based polyurethane. Top non-yellowing water-based polyurethane products include:

  • 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. This is because polyurethane is a clear coat and as such isn’t designed with pigments that will turn white paint to yellow.

As a clear coat, polyurethane is designed to reveal the color of the undercoat or paint underneath. So if you apply polyurethane over white paint, the paint will remain white, only that it will now have a glossy clear film over it.

However, polyurethane can make white paint have a yellowish appearance over time. This is more common with oil-based polyurethane. When this happens, it’s not the white paint underneath that turns yellow. Rather, it’s the polyurethane coating that begins to have a yellow tint.

Since the clears coat is turning yellow due to polymer degradation or UV exposure, it can make the white paint underneath appear yellow making you feel that the polyurethane has turned your white paint to yellow.

Related Read: How To Thin Polyurethane Paint?

FAQ’s

Does Varathane Polyurethane Yellow?

Oil-based varathane polyurethane does yellow. However, water-based varathane polyurethane tends to yellow less. Oil-based varathane yellows more because it has more oils in its formula. 

Does Wipe on Poly Yellow?

All oil-based polyurethane will yellow over time, including poly yellow. However, some oil-based polyurethane tend to last longer before yellowing. It takes wipe on poly more time to yellow than it takes a normal oil-based polyurethane. 

How Long Before Oil-Based Polyurethane Start To Yellow?

The time it takes oil-based polyurethane to yellow depends on a lot of factors. The type of polyurethane, the thickness of the coat applied, and how much the coating gets exposed to UV lights, all determine the time it takes polyurethane to yellow. 

As a rule of thumb, it can take oil-based polyurethane between 6 months and 2 years to develop a yellow tint. It takes water-based polyurethane between 1-3 years to develop a yellow time. However, these are estimated values as the time depends on the factors we mentioned. 

Final Words

Overall, polyurethane turning yellow is common and more common with oil-based polyurethane. The yellowing is due to polymer degradation, UV exposure, or oily deposits.

However, you can lighten the yellowing by scuffing the polyurethane finish with fine-grit sandpaper. This will remove some of the yellowing.

But, is not a guarantee as scuffing is more ideal for removing scratch marks on the polyurethane and not yellowing. The best way to get rid of the yellowing is to strip the polyurethane and start from scratch.

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