Is Polyurethane Good for Outdoor Use?

Is Polyurethane Good for Outdoor Use?

Polyurethane is a popular wood varnish that creates a waterproof, abrasion-resistant, and rich finish for your wooden furniture and fixtures. 

Because of polyurethane’s impressive protective qualities, some people like the varnish for exterior use. But is polyurethane good for outdoor use, let alone safe? 

Well, the answer to that question is a little two-sided. 

What is Polyurethane?

Polyurethane is a type of clear varnish for coating wood and giving it a rich, protective finishing. A polyurethane coating gives the wood a finish resistant to water, abrasion, and solvents. 

Compared to other varnishes, such as simple oil or shellac varnishes, polyurethane varnishes form a tougher, harder, and more water-resistant film. They do not penetrate the wood too deep, and the resultant film sits superficially on top of the surface. As such, polyurethane varnishes are popular for hardwood floors. 

However, polyurethane is unsuitable for soft woods such as pine. Moreover, some woodworkers don’t like using polyurethane varnishes for wooden furniture. 

This is because thick polyurethane films are vulnerable to heat or shock, and exposure to these elements can easily fracture the film, leaving behind white patches on your beautiful wood.

Types of Polyurethane Bases

Initially, polyurethane was made using an oil base. However, restrictions on volatile organic compound (VOC) emissions necessitated the development of alternatives to oil-based polyurethanes. 

  1. Oil-based polyurethane uses various petroleum and mineral solvents as a base for polyurethane solids. The oil turns the wood slightly warmer than its original color even without a stain, and multiple coatings tend to leave a sheen. Oil-based polyurethane dries much slower than its alternatives but requires fewer coatings. 
  2. Water-based polyurethane uses water as a base for carrying polyurethane solids, and the watery consistency necessitates more coats than oil-based polyurethane. It resembles milk, but it dries into a transparent film without changing the color of the wood. 
  3. Water-based oil-modified polyurethane combines the convenience of a water-based poly and the warm-tinted finish of an oil-based poly. It looks cloudy in the can and dries to a warm finish. Furthermore, it dries quickly, requires fewer coats, and cleans up easily with water. 

Types of Polyurethane Finishes

In addition to the different types of bases, polyurethane varnishes also come in different types of finishes. These are: 

  1. Gloss
  2. Semi-gloss
  3. Satin

The type of finish you use doesn’t affect the structure or integrity of the wood. Hence, the choice depends entirely on your personal preference.

However, keep in mind that as the gloss factor increases, imperfections within the wood become more and more visible. Sometimes the imperfections are actually desirable for a certain aesthetic, so personal preference comes into play once again. 

Indoor Vs. Outdoor Polyurethane

There is a lot you can chalk up to personal preference when using polyurethane. However, one thing that restricts you is the composition of the polyurethane. In other words, different compositions make some types of polyurethanes more suitable for indoor use than outdoor use. 

Polyurethane is naturally sensitive to ultraviolet radiation from the sun. Moreover, while it acts as a protective layer for everyday indoor use, the elements are much less forgiving outdoors. Essentially, regular indoor polyurethane cannot withstand the pelting sun or pouring rain. 

Hence, outdoor polyurethane is treated to be able to withstand these harsher elements. Exterior polyurethane typically contains an ultraviolet absorber and polyurethane resin (a flattening agent that reduces sheen). 

Furthermore, you’ll find that all exterior polyurethane either contains an oil base or has been modified with oil. Since oil is hydrophobic, it doesn’t allow the varnish to dissolve and peel off with the rain. 

Can You Use Indoor Polyurethane For Outdoor Use?

Outdoor polyurethane comprises a special composition able to withstand ultraviolet radiation and harsh weather conditions. Hence, you can not use just any polyurethane for outdoor use. 

Instead, you need to make sure that your choice of polyurethane is suitable for outdoor use. Mostly, the packaging specifies whether the product is suitable for interior or exterior use. However, you can also check the ingredients and see whether or not it contains one or more types of oil. 

If you use indoor polyurethane outdoors, it won’t be long before it cracks and starts peeling. 

At the same time, though, you can easily use outdoor polyurethane for indoor use. However, this is unnecessary and overkill since you don’t require that extra bit of protection inside your home. 

Conclusion

Polyurethane is among the most popular wood varnishes. It is waterproof, resistant to abrasion, and gives the wood a rich, glossy finish. 

Outdoor polyurethane is vastly different in composition than indoor polyurethane. Specifically, it is more resistant to ultraviolet radiation and harsh weather. 

Hence, the general rule of thumb is that you can use outdoor polyurethane for indoor use, but not the other way around. 

Warwick Braith

Warwick Braith is a thrill seeker at heart. He loves getting outdoors and testing his limits in the wild. As a blogger for YapQ, Warwick provides readers with insights and tips on how to get the most out of their outdoor experiences. Whether it's hiking, camping, or simply exploring nature, Warwick knows how to make the most of it.

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