DIYers and many homeowners usually have a long list of wood finishes to choose from when shopping for one. These range from natural wood finishes like tung oil, shellac, and linseed oil, to chemically modified finishes like boiled linseed oil, polyurethane, and spar urethane.
While spar urethane is a durable and versatile wood finish, many DIYers and paint technicians often ask: Does spar urethane yellow over time?
Here’s a detailed answer to the question. In this article, you will learn the following:
- What Spar urethane is
- Whether spar urethane yellows over time
- How to deal with spar urethane yellowing
Read on to find out!
What Is Spar Urethane?
Although it is not as popular as many other types of wood finish on the market, Spar urethane is a unique type of varnish, originally designed for protecting wood used in making boats. It is a durable sealer designed to protect the wood from the elements.
It was usually used as a protective coat on the wooden poles that held the sails of boats and ships. These poles were also known as Spars, which could be why it is called spar urethane.
The poles have to withstand harsh weather conditions and serious damage from harmful UV light from the sun. Hence, spar urethane was usually applied to the spar to protect and extend its life span. The design of spar urethane makes it flexible enough to respond to the contraction and expansion of the wooden pole.
But recently, it has begun to feature in many woodworking projects. Perhaps, it is important to understand that spar urethane is essentially a synthetic solution. This solution contains solvents and resins like urethane plastic.
Spar urethane comes in two forms: water-based and oil-based versions. But if you are embarking on a project and want to use spar urethane, perhaps the question to ask is if it yellows over time. Read on to find the answer below.
Does Spar Urethane Yellow Over Time?
Pointedly, the answer to the question will depend on the version of spar urethane you are using. Oil-based spar urethane usually takes on amber or a yellow color over time. It delivers this yellow color slowly after an extended period.
But water-based spar urethane does not deliver a yellowing toe to the wood over time. It is usually a clear finish that does not interfere with the color of the wood, nor does it deliver a yellow or amber tone to the wood.
So, if you want to use spar urethane for your next or current woodwork project and you are worried about the finish turning yellow over time, it would be best to choose a water-based spar urethane.
However, it is important to note that water-based urethane from some manufacturers will turn yellow, especially when you apply them to light wood. You may also encounter the same results if you apply the water-based spar urethane to light stains.
One of the ways you can test the water-based spar urethane you have to see if it yellows over time is to apply it on a test piece of wood. You want to leave the wood in the sun to see how it responds to extreme weather conditions over time to see if it will eventually yellow.
But this can be very time-consuming and can also turn out to be a waste of time if the brand of spar urethane you are using eventually turns yellow.
Ultimate spar urethane is a brand you can trust if you are looking for a water-based spar urethane that will not yellow or turn amber over time. You can do specific research on the spar urethane brand to know what you are buying.
How To Deal with Spar Urethane Yellowing Over Time
Although some manufacturers may argue that their water-based spar urethane will not yellow over time, you may realize that the yellowing cuts across many brands.
Another reason you may see your water-based spar urethane yellowing is that the ultraviolet blocker will not be permanently efficient. Over time, it will lose its efficiency, and the prolonged vulnerability to direct sunlight could also lead to yellowing.
How soon this is likely to happen will usually depend on the brand. But when confronted with this problem, how can you handle the situation?
Perhaps, the first step to limiting the chances of your spar urethane turning yellow, apart from choosing a water-based version, is to avoid using light wood and light-stained wood.
Another thing you can do is scuff the surface of the wood and recoating the wood to remove the yellow hue and enhance the look of the wood. This is straightforward maintenance work. What you need to get rid of the yellow or amber hue are 220 and 150-grit sandpapers.
First, you want to lightly sand the wood surface with 150-grit sandpaper. After cleaning the surface, you want to follow it up with the 220-grit sandpaper for a smoother and cleaner surface. This will eliminate the yellow or amber tone and prepare the wood surface for another application of your water-based spar urethane.
Sometimes, the yellow or amber tone can be caused by the brush you are using to apply your spar urethane to the wood surface. You want to ensure that your brush is a natural bristle brush. It must be made of natural animal hair.
This will also help to prevent any yellowing or amber tone as the natural hairs are less likely to leak any coloring into the wood finish.
This is important because several yellow hue or amber tone delivery in spar urethane finishing can be traced to contamination in the brush used for application. This is why it is very important to use only natural bristle brushes.
You can also take the time to wash the brush, especially if it has been used in any previous project. It does not matter that the brush has been cleaned before. You can wash the brush with dish soap to eliminate any contamination in the bristle.
You want to run the bristle under warm water after washing it with dish soap.
If you have used the brush to apply an oil-based finish before, it would be best to first work the bristle in mineral spirit. You want to swirl the bristle in the cup of mineral spirit for a few minutes in a well-ventilated area.
After swirling, you want to keep the brush on a rag to rest while the rest of the mineral spirit evaporates.
The whole point of the cleaning is to ensure that the brush is free from any contamination that may affect, contribute to, or cause the yellowing of your spar urethane.
How To Get the Best Result When Applying Your Spar Urethane
Water-based urethane is different from oil-based spar urethane. While you may achieve a great result in about 2-3 coats with the oil-based version, you will need to do it differently with the water-based spar urethane.
If you are using a water-based spar urethane, you will need to apply at least four coats of the finish to get the best result. You need to apply the water-based spar urethane in very thin coats. It would be best not to shake or thin the product before use, but you can stir it before and during use.
Normally, water-based spar urethane dries to the touch in about 1 – 2 hours. You want to sand lightly between coats. After applying the last coat, it would be best to leave it to cure for at least 12-24 hours. But the wood surface should be fully cured after 72 hours.
- Do not use steel wool to buff or sand the coats.
- If you want to achieve the best results, it would be best to sand the wood and each coat in the direction of the wood grain. You must ensure that you do not sand the wood against the direction of the wood grain, as this can affect the final quality of the job.
- Ensure to clean the sanded surface with a tack cloth before coating the wood surface.
- It would be best not to over-puddle or overlap during application. This will affect the final quality of the finish. It would be best to apply light coats repeatedly until you get the desired thickness you want.
It is not surprising to find out that many hold the opinion that spar urethane yellows overtime or delivers an amber tone to the wood after a long period. This is because they opted for and applied the oil-based version of spar urethane to the woodwork they worked on.
Over time, oil-based spar urethane will always deliver an amber-yellow tone to the wood. This is because of its design. But the water-based spar urethane differs in this regard.
Generally, the water-based spar urethane does not yellow over time.
The tips above can also help you avoid any possible yellowing. If you cannot avoid it, you can deal with it by applying the scuffing and recoating technique above.
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