Can polyurethane make wood waterproof?

Is polyurethane Waterproof

Use this guide to learn about polyurethane and its efficiency to withstand humidity, water resistance, and other water-related situations.

Polyurethane is one of the most popular finishes used on wood, metals, often on ceramic, containing acrylic and polyurethane as the main ingredients. Mixed up with an array of other adhesives. Available in both varieties in oil-based and water-based formats. Capable of using it for interior and exterior projects. 

Chances are you would get confused in the market when you see dozens of types. Some will say are good for exterior use and others are suitable for interior. And how they react against water is also different.

Therefore, before making your choice, you should research a bit more about the type of polyurethane you would need. As, interior and exterior both impact differently, also the ability to resist water can be different.

Does polyurethane protect the wood from water?

The fact is, wood is always going to absorb water. There’s no way you can achieve %100 waterproof ability, however, the term water-resistant sits better in the place- an achievable property by using polyurethane, and using other types of finishes like linseed oil.

  • Polyurethane is a good choice if you want your wooden piece to last long. On Wood’s surface, it creates a thick plastic-like coat. Tough polyurethane is not %100 waterproof. Nevertheless, you can expect a good water-resistant surface.
  • The polymers” in polyurethane form microscopic bonds, very close to each other they form a chain of polymers which can be described as a coat of plastic. Plastic can help resist water droplets, thus waterproofing abilities are great of polyurethane, capable of resisting warping, swelling, and rotting to any wooden piece when applied.

How much waterproof a wood surface can be?

  • The ability to resist water depends on the layers of coats. Although you can not achieve %100 outcomes yet still a polyurethane surface can hold on to rotting and warping and swelling problems.

How many coats are enough for waterproofing?

  • 5-7 coats of polyurethane can give you maximum protection from water.

If you just apply one coat, after it dries you will have a thin, discontinuous (holey) layer of plastic attached to the wood. Due to the holes in the finish and the thin finish, even small abrasions will wear it away or create more holes, the wood is not waterproof at this point.

  • Putting enough coats, 5 to 7, on the wood will result in a thick and continuous (hole-free) layer of plastic. Water will not penetrate a continuous layer (under normal conditions… we’re not talking about high pressure or prolonged submersion) and if the coat is thick enough, it will remain waterproof after daily use (and won’t warp).

Oil-based or water-based, which is more water-resistant?

From the choices of water-based, or oil-based polyurethane and the modified version water and oil-based. Considering and giving the priority to water-resistant, polyurethane contains oil-based provides a protective and durable coat. 

Here is some information about the types.

  • Oil-based: Using this will create a thick, durable, and easy to clean film. Does not get yellowish, thanks to its UV-resistant ability. Since the oil repels water, ensuring that the film will not let water get soaked up. All the pros make it a suitable choice for waterproofing exterior furniture that not only needs protection from rains but also the sunlight effects.
  • Water-based: Emitting low VOC, make them ideal for interior use such as you can protect your kitchen cabinets, or tabletops using them. And as far as the water in the concern, the coats you apply decide the level of protection you can have. But surefire thing is, compared to oil-based, the durability is less. But the major pro is that the drying time is shorter than oil-based polyurethane.

Polyurethane and water: Verdict

The summed to all the content is that the polyurethane does make a water-resistant surface. Not %100 since no wood finish can achieve that. Here’s what I water-resistant, and pretty much waterproof. 

Over the past five or six years, I have restored and refinished an old desk with polyurethane. 

The finish and wood are still in good condition despite being sprayed with water multiple times. 

Most poly finishes do not hold up well in the outdoors, however. 

As a result of damage from the sun and elements, water may penetrate the wood’s finish. 

For outdoor use, make sure the poly is for exterior use and is UV resistant. 

The finish will protect the wood longer. 

For boats, surfboards, and other projects that will be submerged, at least partially, look for a marine-grade finish (usually an epoxy). It will work better and last longer. (If you do not like the yellow hue of poly, a clear epoxy is also a good choice for other projects as well.)

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