April 12, 2022

Interior vs Exterior Polyurethane

What is Polyurethane?

Polyurethane is a durable type of varnish that comes as microscopic links or chains of resin molecules that will tightly adhere together once the product dries. The finish you’ll get is more abrasion-resistant, solvent-resistant, and water-resistant than other typical vanishes.

What is interior polyurethane?

Water-based interior Polyurethane-Acrylic is a water-based hybrid interior coating that achieves professional results on various wood surfaces. And this is a transparent finish with a high level of hardness and durability. It would help if you didn’t use interior polys outside since they lack the necessary UV-protecting ingredients for exterior finishes. Furniture, floors, cabinets, doors, windows, trim, paneling, and molding are all good candidates for this product.

What is external polyurethane?

ZAR Exterior Oil-Based Polyurethane is an excellent alternative if you’re searching for a solution to enhance the natural color of your hardwood surfaces. The product gives the surface of the wood a subtle hue and a satin sheen.

This solution protects your hardwood surfaces while also adding to the aesthetic appeal of your item. This polyurethane has a sophisticated, modern appearance and offers one of the shiniest polyurethane finishes available, far superior to any water-based product.

The recipe produces a long-lasting, firm finish that is resistant to the elements, particularly UV rays. Antioxidants are included in the composition to ensure that your completed surface does not discolor.

Accidentally used interior polyurethane outside?

Because interior polyurethane does not have the same UV protection as external polyurethane, it will fade if exposed to the sun. If not, it will last for the same amount of time. Re-staining with the same outside color will make it darker. To keep it near what you want, you might need to go lighter with the exterior stain.

Water-based polyurethane 

Water, rather than solvents, is used to transport polyurethane solids in water-based polyurethane coatings. Water-based polyurethane, like oil-based polyurethane, can build a robust protective coating, but it requires more applications.

Because water-based polyurethane dries fast, it is possible to apply more coats in less time than oil-based polyurethane. In the can, water-based polyurethane appears milky white but dries clear. The water-based polyurethane adds a minimal color, if any at all. Water-based polyurethane coatings have essentially slight odor, and cleaning them requires simply soap and warm water.

Water-based polyurethane is the way if you don’t like working with dirty, odorous chemicals. Water-based polyurethane coatings are simple to apply and remove afterward. Water-based polyurethanes are an excellent option if they only require a thin, flexible coating. One coat of oil-based polyurethane is thick, whereas only one or two applications of water-based polyurethane are practically invisible and have almost no build.

Similarly, if you want a hard shell look with the water-based product, multiple coats are required to achieve that effect.

Can you put exterior polyurethane over interior polyurethane?

You can apply exterior polyurethane over interior polyurethane as long as the finished surface or item remains indoors.

If you’re working on a surface that will be open to the elements, you shouldn’t put exterior polyurethane over inside polyurethane. And this is because the internal polyurethane that serves as the base coat would be too weak to withstand the elements outside.

The entire polyurethane coating will scrape off after a while because the base coat (or interior polyurethane) isn’t strong enough, even if the topcoat is a paint for the outside.

Polyurethane comes in two varieties: interior and exterior polyurethane, like most other paints. Both sorts of poly have a lot in common. On the other hand, outer polyurethane originates from additives that make it resistant to UV rays and harsh weather.

On the other hand, interior polyurethane doesn’t include any additives. As a result, the paint isn’t resistant to UV rays or extreme weather. Exterior polyurethane is, therefore, more durable than inside polyurethane.

On a surface or item that will be utilized outdoors, using exterior polyurethane over inside polyurethane will not produce a long-lasting outcome.

You might believe that the external polyurethane will shield the internal polyurethane from UV radiation and bad weather. Genuine, but external polyurethane isn’t wholly impervious to UV radiation and moisture.

The external polyurethane will progressively deteriorate due to prolonged exposure to UV radiation and harsh weather. Because the outer polyurethane wears down over time, it is inside and will eventually get exposed to UV radiation.

Because the internal polyurethane isn’t for enduring regular UV exposure, it will peel off soon. When this occurs, the topcoat (or exterior polyurethane) will follow.

On an external surface, if you use exterior polyurethane over inside polyurethane, the finish will last at most a year before peeling.

Polyurethane vs polyacrylic

Polycrylic is a less durable alternative to polyurethane and is only ideal for use on interior surfaces such as cabinets, furniture, and trim. The base of the formula is acrylic, with polyurethane added for improved adhesion and durability. Polycrylic is more environmentally friendly because it uses a water-based solution. 

It is unsuitable for outside or surfaces subject to wear, such as flooring or surfaces exposed to water. Other floor treatments, both solvent and water-based, are designed expressly for foot activity and can withstand wear and tear.

Oil-based polyurethane gives the wood a subtle amber tone, so it’s not the best choice over a pure-white painted finish. Although water-based polyurethanes don’t have the amber cast, they can cause white or light-colored surfaces to be yellow or slightly foggy over darker finishes like milk paint after drying.

Polycrylic, on the other hand, retains a clear, non-yellowing finish that won’t alter the appearance of lighter woods like maple or birch or white-painted surfaces. However, polycrylic should not be used over dark-colored paints or red mahogany stains, as its clear look can turn opaque or milky.

More importantly, the following should be taken into account the next time you’re in the paint aisle looking for the perfect protective finish:

Choose polyurethane if your project is outside or will be subjected to abuse indoors (such as flooring). It’s a challenge. Long-lasting and straightforward to operate. However, it will off-gas throughout the drying process because it is oil-based, so make sure you have enough ventilation. 

Polyurethane also gives any surface, whether bare wood or paint, an ember cast. Polyacrylic is the way to go if you’re working on a project inside, such as light-colored furniture or interior trim. It doesn’t have the same strong odor as polyurethane, and it’s easy to clean with soap and water.

Is polyurethane waterproof?

Yes, to a certain extent. Some polyurethanes are more absorbent than others due to a variety of variables. Compared to other known materials, thermoset polyurethanes can have nearly minimal water absorption depending on the physical qualities and composition.

Polyurethane clear coat?

A transparent coat made of oil-based polyurethane is relatively long-lasting. This oil-based product adds a subtle color tone and brings out the richness of wood, making it ideal for stained wood, especially hardwood floors.

Can interior polyurethane be used outside?

Polyurethane may bring out the beauty of wood because it is a clear finish. Attempting to apply an interior polyurethane outside will rapidly peel off the finish. Oil-based polyurethanes will make up the majority of external polyurethanes.

What’s the difference between indoor and outdoor varnish?

When the finished object is used indoors, you can use the exterior-grade varnish over the interior-grade paint, but not if it will be suitable outdoors. Even if the varnish is outdoor quality, exposure to the weather will deteriorate the paint layer and cause it to fail.

Interior varnishes are not suitable outside as described on the tin since they lack UV resistance and qualities to endure the elements.

Can indoor varathane be used outdoors?

Varathane Premium Diamond Outdoor Finish is a water-based product that delivers maximum protection for your outdoor wood projects. Most exterior polys are valuable indoors but lack UV-protective ingredients, but you shouldn’t use internal polys outdoors.

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