Last Updated on August 27, 2023 by Ernest Godia
Polyurethane is one of the most popular wood finishes for its versatility and long-lasting performance. Its exceptional durability makes it well-suited for high-traffic areas and surfaces that are subject to wear and tear.
Wood surfaces coated with polyurethane have incredible resistance to moisture and other weather elements likely to cause discoloration and premature deterioration.
However, not all polyurethane is created equal. Knowing the various types of polyurethane sealants and finishes can help you choose better for your project.
This article discusses the two primary types of polyurethane sealants for wood and their characteristics. You will also find the various polyurethane finishes and how best to use them.
What is Polyurethane?
Polyurethane is a type of synthetic polymer commonly used as a versatile material in various industries, including construction, automotive, furniture, and coatings.
In the context of wood finishes, polyurethane refers to a type of coating that contains polyurethane resins. Polyurethane finishes are applied to wood surfaces to provide protection, increase durability, and enhance the appearance of the wood.
Types Of Polyurethane Sealants for Wood
Polyurethane is available in two primary types: oil-based polyurethane and water-based polyurethane. Here’s an overview of each type:
1. Oil-based polyurethane
Oil-based polyurethane is a traditional and widely used type of polyurethane finish. It is solvent-based, typically made by combining polyurethane resins and dry oils like tung or linseed.
Characteristics of oil-based polyurethane
- Durability: Oil-based polyurethane provides excellent durability and protection for wood surfaces. It forms a hard protective shell over wood and offers resistance to scratches, heat, moisture, water, insect infestation, and fungi attack.
- Richness and Depth: Oil-based polyurethane tends to enhance the natural beauty of the wood, providing a rich, amber color and deepening the appearance of the grain. It can give the wood a warm and traditional aesthetic.
- Drying Time: Oil-based polyurethane takes longer to dry than the water-based option. It takes at least 24 hours or a few days to dry to touch and even longer to fully cure. Environmental factors like low temperatures and high humidity slow down the drying process.
- Strong Odor and VOCs: Oil-based polyurethane has a strong odor and contains higher levels of volatile organic compounds (VOCs). Adequate ventilation is necessary during application to minimize fumes.
- Toxicity: Oil-based polyurethane emits toxic fumes that are harmful to your health and the environment. Prolonged exposure to these fumes can damage the eyes, nervous system, and the brain. Therefore, working in a well-ventilated space and wearing protective gear is recommended when using oil-based poly.
- Application: Oil-based polyurethane is available in brush-on and spray-on formulations. Because of its slow drying quality, it is easy to apply, and you can overlap and smooth out any imperfections and paint drips.
- Ease of Cleaning: Oil-based polyurethane is challenging to clean. It comes off with paint thinners or mineral spirits.
Pros and cons of oil-based poly
Here are some advantages and drawbacks of using oil-based polyurethane:
- You only need a few coats for proper coverage.
- It forms a durable protective coating on wood.
- It enhances the natural beauty of wood.
- It is self-leveling
- Best for waterproofing and weatherproofing wood
- It is highly toxic and emits a bad odor.
- It takes longer to dry and cure
- It only cleans with paint thinners and mineral spirits.
When to use oil-based types of polyurethane
Here is when to consider using oil-based polyurethane:
- When covering surfaces prone to heavy traffic and excessive duress like cabinets, railings, wood floors, and countertops.
- Oil-based polyurethane is better on outdoor furniture pieces on your deck or front porch, exposed to harsh elements all year.
2. Water-based polyurethane
Water-based polyurethane is the more eco-friendly type. It contains water as its base instead of organic solvents. Being waterborne means the polyurethane resin is dispersed in water.
Characteristics of water-based polyurethane
- Durability: Water-based polyurethane is traditionally less durable than oil-based poly. However, modern water-based brands are just as durable as oiI-based versions. But you must apply several coats because this type of poly has fewer solids.
- Richness and Depth: Water-based polyurethane dries clear and doesn’t alter the color of the wood. It looks better on lighter-colored woods like maple or birch and white or gray stained surfaces. Water-based polyurethane doesn’t turn yellow with time.
- Drying Time: Thin coats of water-based polyurethane dry to the touch in 2-4 hours and completely dry within 24-48 hours. Expect water-based poly to take approximately 2 weeks to cure, but you can let it cure for up to 30 days.
- Toxicity: Water-based polyurethane contains lower levels of VOCs, making it more environmentally friendly. It emits a milder odor and is hence healthy for indoor usage.
- Ease of Cleaning: Water-based polyurethane cleans easily with soap and water, which is convenient for correcting errors made during application.
Pros and cons of waterborne polyurethane
Below are the advantages and limitations of using a water-based-polyurethane sealer:
- It is less harmful to you and the environment.
- It is non-flammable
- It dries and cures fast
- Cleans easily with soap and water
- It doesn’t change the natural color of the wood or turn yellow over time
- It raises the wood grain, and you spend more time sanding
- It is sensitive to harsh weather
When to use water-based types of polyurethane
Here is when water-based polyurethane finishes are most appropriate:
- If you want a non-yellowing light-colored wood.
- When coating indoor surfaces as it is less toxic.
- On surfaces that need high scratch resistance and fast drying products.
- On children’s furniture and toys
Types of Polyurethane Finishes for Wood
The sheen level in a finish (or finish type) is determined by the degree to which the surface reflects light. Both water and oil-based polyurethane are available in four sheen levels or basic types of polyurethane finishes: matte, satin, semi-gloss, and gloss.
1) Matte finish
Matte is the flattest and reflects light the least compared to the other polyurethane finishes. However, matte’s low luster enhances its ability to hide any blemishes and scratches on the surface.
2) Satin finish
Satin is the perfect choice for DIYers who don’t want the flat matte finish and, at the same time, don’t intend to achieve a glossy appearance. Satin sheen is right between matte and glossy. In addition, it hides unappealing imperfections of the wood surfaces pretty well.
3) Semi-gloss finish
Polyurethane with a semi-gloss sheen leaves surfaces with a more lustrous shine than a satin finish.
Semi-gloss finishes enhance the natural beauty of the wood and, at the same time, make scuff marks and scratches more visible. Semi-gloss sheen is high maintenance and demands effort and reapplication to sustain the glow. Apply semi-gloss polyurethane to areas that receive less traffic.
4) High-gloss finish
It is hard to miss a surface with a high-gloss polyurethane finish. The level of shine and sheen will catch your eye.
High-gloss polyurethane gives furniture pieces a touch of sophistication and a luxurious appearance. The downside to the high-gloss sheen is it reveals every little scuff mark, ding, or scratch. Use this sheen on surfaces with less traffic.
Tips for Applying Oil-based Polyurethane
Here are a few pointers when applying oil-based polyurethane:
- Use a paint thinner, mineral spirits, or naphtha to achieve the perfect consistency. Read the manufacturer’s instructions to know if they recommend thinning their product.
- Apply the sealant with a natural bristle brush, as other types tend to leave brush strokes or opt for a foam brush.
- Don’t shake the can of paint before opening, as that creates air bubbles in the finish.
- Apply thin, even coats and follow the wood grain.
- Lightly sand the dry coat of polyurethane before adding the subsequent layers. Remove the sanding dust with a tack cloth or vacuum, but do not sand the final coat.
Tips for Applying Water-based Polyurethane
Here are useful tips when applying water-based polyurethane:
- Water-based poly doesn’t mix with oil-based products, and you’ll need to scuff the surface before application for better adherence. If you skip sanding, water-based polyurethane will form beads on the surface.
- The application technique is similar to that of oil-based polyurethane. Use a synthetic bristle brush, foam brush, or rag. When applying polyurethane with a rag, ensure the cloth is lint-free and follow the wood grain.
Common Polyurethane Derivatives Used In Woodworking
Here are other types of polyurethane that you are likely to encounter in your DIY woodworking journey:
- Polyurethane Adhesives and Binders
Polyurethane resin makes an excellent adhesive that creates strong and durable joints.
Polyurethane adhesives are available in various pigments to obtain the desired color. Polyurethane adhesives work best on moist surfaces, like wood, and are suitable for outdoor surfaces.
Polyurethane binders are superb eco-friendly adhesion agents. Polyurethane binders work wonders on surfaces with materials least likely to bond. Polyurethane adhesives and binders resist organic solvents, heat, oils, and plasticizers.
- Polyurethane coating
Polyurethane coating is often used on floors as it is more elastic and durable than epoxy.
Polyurethane coating protects surfaces from the elements, heat, light, abrasion, and deterioration. You can customize polyurethane coatings in muted, glossy, opaque, or transparent formulas. Polyurethane coatings are immune to dents, scratches, and abrasions.
- Waterborne Polyurethane Dispersions (PUDs)
Polyurethane dispersion comprises polyurethane polymer resin dispersed in water rather than a solvent. PUDs are equally as effective as their solvent-based analog counterparts. PUDs are flexible, environmentally friendly, and dry with varying hardness ranges.
They are gaining popularity for their zero to very low levels of VOCs. PUDs are durable and resistant to yellowing, cracking, or peeling. The downside is they are quite pricey.
The food industry, pharmaceuticals, hotels, restaurants, hospitals, and nursing homes widely use polyurethane dispersions.
Types of Polyurethane Finishes: Conclusion
Polyurethane has numerous uses, and its versatility makes it challenging to track all its applications.
In woodworking, polyurethane is typically used as a finish, and you choose between water-based and oil-based polyurethane sealants. These sealers are available in various sheens, depending on your preference.
A coat of polyurethane protects surfaces against heat, moisture, light, insect and fungi damage. Polyurethane is the best solution to prolong the lifespan of your wood. You can never go wrong with a coat of polyurethane.
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