Will Water-Based Polyurethane Yellow?

We all have a pretty good idea of the value of a topcoat on our stained projects.  Stains will enhance the wood’s appearance and grain and provide color to the wood.

However, stains offer no protection to the wood.  

We know the enemies of wood, too:  water, heat, sun, and its UV rays.  Each of these will damage wood, some quickly, like heat, and others over time, like water and the sun with its UV rays.  When it comes to topcoats, some will provide strong protection against one or more of those enemies, and that’s why we use them.

However, the use of a topcoat can also carry its own risk of discoloring over time.  That discoloring takes the form of yellowing.  It can become pronounced enough that it can become necessary to refinish a project in a few years to refresh its appearance.  Yellowing can be annoying, especially after we have worked so hard to craft a beautiful piece of furniture, countertop, or cabinet.

How can we avoid that yellowing?  Are there topcoats that won’t yellow, or at least yellow less than others?

What Is The Benefit Of A Topcoat on Stained Wood?

A topcoat is a clear finish that is applied to wood after it has been stained. The topcoat protects the stain from scratches, water, and other damage. It also enhances the color of the stain and gives the wood a finished look.

There are many different types of topcoats available, including polyurethane, varnish, and shellac. Each type of topcoat has its own advantages and disadvantages. Polyurethane is the most durable type of topcoat, but it can be difficult to apply, and it can yellow over time.

Varnish is less durable than polyurethane, but it is easier to apply, and it does not yellow as much. Shellac is the least durable type of topcoat, but it is the easiest to apply, and it does not yellow at all.

The best type of topcoat for you will depend on your specific needs and preferences. Consider the durability, ease of application, and yellowing of each type of topcoat when making your decision.

Here are some of the benefits of using a topcoat on stained wood:

• Protection: A topcoat protects the stain from scratches, water, and other damage. This can help to keep your wood looking its best for years to come.
• Enhancement: A topcoat can enhance the color of the stain and give the wood a finished look. This can make your wood furniture or other projects look more professional and polished.
• Ease of cleaning: A topcoat can make it easier to clean your wood furniture or other projects. This is because the topcoat will create a barrier between the wood and dirt, dust, and other pollutants.

We’re all in the habit of giving our woodworking projects a topcoat, and we know the results, so no surprises there.  We look for a durable finish to provide protection against all of wood’s enemies, and polyurethane is on that list.

What is Polyurethane?

Polyurethane is a type of polymer that is made by reacting a polyol with an isocyanate. Polyurethanes are used in a wide variety of applications, including:

• Adhesives: Polyurethane adhesives are used to bond a variety of materials, including wood, metal, plastic, and glass.
• Coatings: Polyurethane coatings are used to protect and finish a variety of surfaces, including wood, metal, plastic, and concrete.
• Foams: Polyurethane foams are used for a variety of applications, including insulation, cushioning, and packaging.
• Elastomers: Polyurethane elastomers are used for a variety of applications, including seals, gaskets, and hoses.
• Molds: Polyurethane molds are used to create a variety of objects, including toys, furniture, and medical devices.

Polyurethanes are a versatile and durable material that is used in a wide variety of applications. They are available in a variety of forms, including liquids, solids, and foams. Polyurethanes can be modified to have a variety of properties, including hardness, flexibility, and water resistance.

The polymers and urethanes are mixed and suspended in a medium or solvent, and the “plastic” and “rubber” qualities of the two, respectively, form the clear and somewhat thick topcoat we know.  The poly can be thinned for application, and this is a customary practice for making the application easier.

We’ve written extensively about polyurethanes, including choosing the best poly for your project,  how many coats of poly you should apply,  and how to clean up your brush after applying polyurethane.  You can use the search feature in the upper right corner if you have a particular question about using polyurethane as your topcoat.

What Are The Types of Polyurethanes?

There are two main types of polyurethanes, and the distinction has to do with the medium or solvent the combined polymers and urethanes are carried by in the can.  Each has its own benefits and detriments, including dry time for each, and we’ll address those shortly.

Water-Based Polyurethane

Water-based polyurethane is a type of polyurethane that is made with water as the solvent. This makes it less toxic and easier to clean up than oil-based polyurethane. Water-based polyurethane is also less likely to yellow over time, making it a good choice for projects that will be exposed to sunlight.

Here are some of the benefits of using water-based polyurethane:

• It is less toxic than oil-based polyurethane.
• It is easier to clean up than oil-based polyurethane.
• It is less likely to yellow over time than oil-based polyurethane.
• It is available in a variety of finishes, depending on the look you want to achieve for your project.  The finishes include satin, semi-gloss, and gloss.

If you are looking for a polyurethane that is less toxic, easier to clean up, and less likely to yellow over time, then water-based polyurethane is a good option. It is available at most home improvement stores and online retailers.

Here are some tips for using water-based polyurethane:

• Apply it in thin coats.
• Use water-based poly on water-based stains
• Allow each coat to dry completely before applying the next coat.
• Sand between coats to create a smooth finish.
• Refinish your project every few years to maintain its appearance.

This is probably the poly most choose for their smaller projects and projects that will not experience a lot of wear and tear, such as flooring.

Oil-Based Polyurethane

Oil-based polyurethane is a type of polyurethane that is made with oil as the solvent. This makes it more durable and water-resistant than water-based polyurethane, but it is also more toxic and difficult to clean up. Oil-based polyurethane is typically used for projects that will be exposed to high wear and tear, such as floors, countertops, and furniture.

Here are some of the benefits of using oil-based polyurethane:

• It is more durable than water-based polyurethane.
• It is more water-resistant than water-based polyurethane.
• It provides a harder finish than water-based polyurethane, although this is beginning to change as a result of modifications and advancements in the manufacture of water-based polys.
• It is available in a variety of finishes, again depending on the look you want to achieve.  The finishes include satin, semi-gloss, and gloss.

If you are looking for a polyurethane that is durable, water-resistant and provides a hard finish, then oil-based polyurethane is a good option. It is available at most home improvement stores and online retailers.

Here are some tips for using oil-based polyurethane:

• Apply it in thin coats.
• Use oil-based poly on oil-based oil-based stains
• Allow each coat to dry completely before applying the next coat.
• Sand between coats to create a smooth finish.
• Use a respirator when applying oil-based polyurethane to avoid inhaling the fumes.
• Clean up spills immediately with mineral spirits or paint thinner.

Oil-based polyurethane can take several days to dry completely, so it is important to plan accordingly. It is also important to note that oil-based polyurethane can yellow over time, so it may need to be reapplied every few years.  There we are – the tendency for oil-based poly to take on a yellow tint.

Oil-based polys contain VOCs, volatile organic compounds, and this is the toxicity mentioned above. 

Volatile organic compounds (VOCs) are a group of chemicals that have a high vapor pressure and low water solubility. This means that they evaporate easily at room temperature and are not easily absorbed by water. VOCs are found in many products, including paints, varnishes, cleaning products, and personal care products.

VOCs can be harmful to human health. They can irritate the eyes, nose, and throat, and they can also cause respiratory problems, such as asthma. A respirator should always be used when applying oil-based poly, as well as safety glasses and gloves, and the room should be well-ventilated during the long drying period.

VOCs can also be harmful to the environment. They can contribute to smog formation, and they can also damage plants and animals.

Water-Based Polyurethane And Yellowing

We mentioned that oil-based poly will take on a yellow tint over time, and when this happens, we want that yellowish tint gone and end up refinishing the piece.  Can yellowing be avoided, and is water-based poly the answer?

Water-based polyurethane is less likely to yellow than oil-based polyurethane, but it can still yellow over time. The amount of yellowing will depend on the quality of the polyurethane, the number of coats applied, and the amount of exposure to sunlight and UV rays.

Sunlight and its UV rays can be harmful to unfinished and finished woods if the finish used has no tint or other protective elements added, also.  Wood will eventually crack after a few years of UV rays. 

To minimize yellowing, use a high-quality water-based polyurethane and apply multiple thin coats instead of a few thick coats. You should also avoid applying polyurethane in direct sunlight or in high-humidity conditions.

If you are concerned about yellowing, you can use a non-yellowing polyurethane. These products are typically more expensive than water-based polyurethane, but they will not yellow over time.

Here are some tips to help prevent yellowing of water-based polyurethane:

• Use a high-quality water-based polyurethane.
• Apply multiple thin coats instead of a few thick coats.
• Allow each coat to dry completely before applying the next coat.
• Avoid applying polyurethane in direct sunlight or in high-humidity conditions.
• Refinish your project every few years to maintain its appearance.

What Is A Non-Yellowing Polyurethane?

A non-yellowing polyurethane is a type of polyurethane that does not yellow over time. This type of polyurethane is typically made with water-based or urethane-based solvents, which do not contain the same chemicals that can cause yellowing.

Non-yellowing polyurethane is a good choice for projects that will be exposed to sunlight or other sources of UV light, as it will help to protect the wood from fading.

Here are some of the benefits of using non-yellowing polyurethane:

• It will not yellow over time, even when exposed to sunlight or other sources of UV light.
• It is water-based or urethane-based, which makes it less likely to yellow than oil-based polyurethane.
• It is easy to apply and clean up.
• It is available in the same variety of finishes we mentioned earlier.  Those include satin, semi-gloss, and gloss.

Non-Yellowing Products To Consider

In this category, you might consider MinWax Polycrylic, a poly that is easy to use and designed to dry quickly and clear, and does not turn that yellow tint we want to avoid.  We’ve all seen yellowed polyurethane and become frustrated by it after working hard on a piece of furniture.

When using polycrylic, pay attention to the weather and be sure to apply it in thin coats.  Water-based polyurethane products are sensitive to weather, so use it on a benign day – not too hot or cold, not too humid or dry. 

Another product to consider is Varathane Polycrylic. 

Varathane Polycrylic is a water-based polyurethane that is designed to be non-yellowing. However, it is possible for it to yellow over time, especially if it is exposed to sunlight or other sources of UV light. To minimize yellowing, it is important to apply Varathane Polycrylic in thin coats and allow each coat to dry completely before applying the next coat.

It is also important to avoid applying Varathane Polycrylic in direct sunlight or in high-humidity conditions.

If you are concerned about yellowing, you can use a non-yellowing polyurethane. These products are typically more expensive than water-based polyurethane, but they will not yellow over time.

Here are some tips to help prevent yellowing of Varathane Polycrylic:

• Apply Varathane Polycrylic in thin coats.
• Allow each coat to dry completely before applying the next coat.
• Avoid applying Varathane Polycrylic in direct sunlight or in high-humidity conditions.
• Refinish your project every few years to maintain its appearance.

While there is always the chance of yellowing over time with any poly, some are less likely, as we havr presented.  Still, you should plan on polyurethane yellowing over time and expect you will want to refinish your project every few years.  To minimize the yellowing process for an extended period, though, keep the project out of the sun and avoid UV exposure.

Suggestions for Other Non-Yellowing Finish

We’ve mentioned water-based poly as less likely to yellow over time, but there are other topcoat finishes that are not likely yellow, also. 

They include shellac, wax, and epoxy.  Each has its qualities to consider, but none of them will yellow over time.

Video Suggestion

It’s long, at 15 minutes, but it is packed with information about the yellowing process and topcoats.  There’s a little something about Polycrylic, Shellac, wood tannins (the occasional cause of yellowing with a water-based poly), and more, and is worth a watch.

Not everything is perfect, and we know that in woodworking.  But, when it comes to that awful yellow tint, there are steps you can take to avoid it. Still, refinishing a project in several years won’t hurt, and who knows what advancements will be made in polys and other topcoats.  Stay current in your topcoat knowledge.