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Polyurethane is a clear coating commonly used to protect wood surfaces such as floors, countertops, and tables. This paint is so durable because of the microscopic resin molecules that stick together as the polyurethane dries. Therefore, this coating is highly resistant to abrasion, water, solvents, impact and other damage. Adding polyurethane to your finishes will improve their appearance and help them last much longer.
- 1 What is polyurethane?
- 1.1 Oil-based polyurethane
- 1.2 Water based polyurethane
- 2 How many coats of polyurethane should I use?
- 3 Polyurethane application
- 4 step-by-step instructions for applying polyurethane
- 4.1 Work area
- 4.2 Preparation
- 4.3 Surface sealing
- 4.4 Apply primer
- 4.5 Wet sanding of the first layer
- 4.6 Apply subsequent coats
- 4.7 Surface polishing
- 6 frequently asked questions
- 6.1 How long should I wait for the polyurethane to dry?
- 6.2 What is the best temperature to dry polyurethane?
- 6.3 How can I remove the bubbles?
- 6.4 How can I remove brush strokes?
What is polyurethane?
You can get both oil-based and water-based polyurethanes, although the latter has only recently been developed. Oil-based polyurethane is a type of alkyd paint that has been combined with polyurethane resin.
Almost all types of oil-based varnishes and paints contain the resin known as alkyd, and the addition of polyurethane resin improves the durability of the alkyd varnish. Thus, the resistance of a polyurethane paint to heat, scratches and water can be attributed to the presence of the polyurethane resin.
The introduction of water-based polyurethane involves the combination of polyurethane with an acrylic resin. Therefore, these paints are not as durable as oil-based ones.
Alternatively, you can use an oil-modified, water-based polyurethane. This means it has the durability and warmth of oil-based polyurethanes, plus the quick-drying, low VOC, low odor, and easy-to-clean properties of a water-based polyurethane.
There are a number of pros and cons to using oil or water based polyurethanes and the number of coats of polyurethane you need depends on the type of polyurethane used. The choice depends on your preferences and the needs of your specific project.
oil based polyurethane
Oil-based polyurethane paints have a thick consistency and are extremely durable once cured. This type of polyurethane can be difficult to obtain due to the high levels of volatile organic compounds (VOCs) it produces.
The question arises whether one layer of polyurethane is enough for an oil-based product. The answer to that is that you need three to four coats of this clear coat for the best results. However, this type of polyurethane takes a long time to dry, which means you have to wait longer between coats.
The varnish leaves an amber tint on the surface, which is especially noticeable on lighter woods such as oak or birch, adding warmth to the color of the wood. You can remove excess polyurethane paint with thinner.
Water based polyurethane
Water-based polyurethane is much better for you and the environment due to its low VOC emissions. This type of polyurethane dries quickly and is self-leveling. Although this polyurethane is excellent to work with due to minimal odor, care must be taken as the water base can cause the wood grain to lift.
The effect water-based polyurethane has on a wood surface makes one wonder how many coats of polyurethane are needed. Is a layer of polyurethane enough to protect the wood? Water-based polyurethanes require just a few coats of paint due to the high grain of the wood, which means you'll need additional coats to smooth the surface. The thin, watery consistency of this polyurethane also increases the need for more coats.
We recommend applying four to five coats of water-based polyurethane to the surface of the wood.
This polyurethane may appear milky white at first, but once dry it is crystal clear, making it ideal for preserving the natural tone of a wood surface. This polyurethane is also less likely to yellow over time. You can clean this polyurethane with soap and water and avoid ammonia-based cleaners once the polyurethane has cured.
How many coats of polyurethane should I use?
Many people ask the question: "Is one layer of polyurethane enough?" Most of the time several coats of polyurethane are needed to adequately protect the surface of the wood. Generally, you will need more coats of water-based polyurethane than you would with an oil-based product.
Water-based polyurethanes are thinner liquids, which means they require four to five coats. Oil-based polyurethanes are thicker and require three to four coats.
The total number of layers depends on the amount of traffic and usage that particular surface experiences.
How to apply polyurethane
Polyurethane can be applied by brush, rinse or spray. Although spraying is the most common application technique, people sensitive to fumes and VOCs should avoid using spray polyurethane.
spray polyurethanesThey are ideal for rough or difficult surface applications as they work similar to spray paint. Spray polyurethanes require between five and six coats due to their thin consistency. However, you do need to work on your application technique, as these types of applicators tend to leave drips.
brushable polyurethanesthey are ideal for flatter surfaces where a thick layer of durable polyurethane is needed. They can cover a large surface area because the brushes retain a large amount of substance. You can also use a foam brush to minimize stickiness.
you can use onepolyurethane cleaningFor irregular and contoured surfaces such as trim and handrails. These are places where brushing can leave drips. You will need several coats of this polyurethane as it has a thinner consistency than brush-on products.
Step-by-step instructions for applying polyurethane.
polyurethane applicationWith a wooden surface it can seem difficult if you are not sure what you are doing. We've outlined the key steps for you to apply your polyurethane paint like a pro.
- Regardless of your polyurethane VOC levels,Always be sure to work in a well ventilated area with good air circulation.
- work insideto prevent dust, insects and other contaminants from falling onto the drying polyurethane surface.
- Always use the proper protective equipment.This includes a respirator and safety glasses.
- Work on a level surfaceThis allows your polyurethane to self-level with less chance of dripping.
- Have a bright light ready.This allows you to see any blemishes, brush marks and the like before the polyurethane dries and gives you time to fix it.
- Before applying polyurethane, you must prepare the wood surface.First, make sure there are no obstacles.
- Sand the surface of the wood until it is smooth.Start with a coarser 100 grit and slowly work your way up to a finer 220 grit.
The finer grit of sandpaper will help remove the deep scratches left by the coarser sandpaper.
- Use a vacuum with a soft brush to remove any remaining dust and dirt.Wipe surface to remove excess oil or debris.
- If you want to work with a water-based polyurethane, first dampen the surface of the wood to enhance the grain.You can then go over the surface with 220 grit sandpaper to smooth it out. This is particularly useful later, as water-based polyurethanes tend to reinforce the grain of the wood.
- When working with porous surfaces like wood, it is important to apply a coat of sealer to prevent blistering.To do this, you need to thin the polyurethane so that it can be used as a sealing coat.
- thinner polyurethaneit is simple:Simply take 2 parts oil-based polyurethane to 1 part mineral turpentine and mix in a pitcher with a stir stick. Water-based polyurethanes can be thinned with water.
- Use a brush to apply the sealer in long, even strokes.To do this, use a natural bristle brush and dip it into the mixture about an inch. Take care to collect the droplets and smooth them back to the surface.
- If you plan to apply a water-based polyurethane to an oil-based stain,You will need to further prepare the surface to allow for proper adhesion. Use some steel wool to roughen the surface to maximize the bonding process.
Apply the first layer
- The first coat of polyurethane can be applied 24 hours after applying the sealer.The sealing layer must be completely dry.
- Never dilute that first layer,as this affects the pasting process.
- The application process for oil-based polyurethane is slightly different than for water-based polyurethane.Therefore, we have described both processes for you.
- Get an even layer by overlapping the brush strokes.Be sure to catch any drips.
Application of an oil-based polyurethane coating.
- You need a brush with soft natural bristles, otherwise you can use a foam brush.Avoid using brushes with cheap bristles as this will cause streaks and scratches. Foam brushes are ideal for flat surfaces, while bristle brushes are better for finer details.
You can dip it directly into the can with a bristle brush. However, do not wipe the edge of the can as this can cause blisters. Instead, tap the center of the can with the brush to remove excess product.
- Apply an even coat that is almost thick but not too thin either.Brush in long, straight, even strokes from top to bottom. Any bubbles left on the surface should pop on their own.
- For maximum protection, you need at least two to three coats.You need to sand the surface between each coat.
Application of a water-based polyurethane coating
- Using a foam brush or cloth, apply a thin coat of water-based polyurethane.Do not apply too much polyurethane in one coat, as this can cause the wood grain to rise to the surface.
- It is not necessary to sand the surface between coats of water-based polyurethane,but it's always better to do it anyway.
- For a lightly used surface, you need at least three coats.Apply at least four coats in high traffic areas.
Wet sand the first coat
- After the first coat of polyurethane has dried for 24 hours, you can remove small bumps and blemishes by sanding the surface with water.Use 400-grit fine sandpaper and a block of sandpaper.
- Dip the sandpaper in water frequently and use circular motions.Be sure to use enough water to properly saturate the sandpaper, as this will prevent it from damaging the polyurethane finish. You want to sand the surface down just enough to remove any blemishes.
- Continue sanding the polyurethane until smooth.You can then clean the surface with a damp cloth and dry completely with a clean, lint-free cloth.
Apply your subsequent coats
- Apply subsequent coats only after the polyurethane has dried for 24-48 hours.elapsed since the first coat was applied.
- Rectified between layers of polyurethanenot always necessaryHowever, because this product dries so quickly, it is often necessary to remove some dust before applying the next coat. This ensures an even and level surface.
- Do not sand the final coat of polyurethane.You will buff the final coat to an attractive shine.
When applying polyurethane, always brush in the direction of the grain and apply the compound as thin as possible.
Rectified between layers of polyurethane
- When sanding between coats of polyurethane, always use very fine grit sandpaper.Allow at least 24-48 hours for the polyurethane to dry before applying the next coat.
- You will need to sand more thoroughly for gloss finishes than for semi-gloss or satin finishes.This is because even the smallest blemishes will show up in a glossy finish, while smoother finishes tend to hide these blemishes. Also, due to their smoothness, glossy surfaces do not adhere as well and therefore require a rougher surface to adhere to the next coat.
- Take care when sanding the polyurethane with a sanding block.While useful for flat surfaces, the pad can clog up the sandpaper and cause "calluses," creating deeper scratches in the surface that may not cover up with the next coat.
- You can also use steel wool or a synthetic scouring pad.instead of sandpaper, but these won't work as well. Steel wool also often leaves faint steel marks that only become apparent when they start to rust.
polished on the surface
- You should buff the last coat of polyurethane surface, especially if you sanded the second coat with water.Allow the polyurethane to dry for 48 hours before attempting to polish the surface.
- Choose a high-quality polishing paste or polishing paste.You need a product fine enough to remove the scratches from the sandpaper, returning the polyurethane to its original shine.
- Take a clean cotton cloth and moisten it with a little water.Apply the polishing paste and rub the surface in a circular motion.
- Allow the surface to dry completely, then use a clean, dry cloth to buff the surface.If the surface finish remains a bit cloudy, simply apply more polishing paste, followed by a surface polish. Keep doing this until you get the shine you want.
Tips and tricks for working with polyurethane
- Never shake your polyurethane can or bubbles will form.Instead, gently stir the mixture.
- Always use a good quality natural bristle brush to apply oil based polyurethane.Synthetic bristle brushes are more prone to air pockets.
- Use synthetic fiber brushes for water-based polyurethanes🇧🇷 These brushes include polyester, nylon or a mix of both. Using foam rollers or brushes will cause blisters.
- thinner polyurethaneallows faster drying.
- Never dilute polyurethane primer.You can thin the base coat and any future coats, but you should never thin the first coat, as this will affect the adhesion of the polyurethane to the surface.
- Moisten the brush with a solvent during use.You can make cleaning the brush easier by soaking it in mineral spirits or water, depending on whether you're using an oil- or water-based polyurethane.
- Never rub the brush on the rim of the polyurethane can.This leads to blisters. Instead, tap the brush across the bowl to remove any excess mix.
- Always plan or wipe in the same direction as the grain of the wood.Try to work the polyurethane into the pores of the wood as much as possible to ensure an even finish.
- You can minimize dripping by applying thinner coats.It is easiest to create a thin coat by mopping or spraying the polyurethane. If all else fails, you can use a razor to remove any runoff or drips.
How long should I wait for the polyurethane to dry?
Most oil-based polyurethanes require at least 24 hours to dry. Due to their thinner consistency, water-based polyurethanes dry faster and feel dry in less than six hours. Polyurethane drying time increases with low temperatures, high humidity, poor ventilation and thick coats.
At what temperature does polyurethane dry best?
The best temperature for optimum polyurethane drying time is 77 degrees Fahrenheit. However, this drying time is ventilation and humidity dependent and requires 50% humidity relative to temperature.
How can I remove the bubbles?
Bubbles in a polyurethane finish rarely go away on their own. You have two options for dealing with these unwanted bubbles: The first is to clean the bubble-filled liner with a cloth soaked in white spirit or mineral spirits. Go over the surface for 15-30 minutes to remove bubbles without damaging the polyurethane surface. Wipe off excess leaving it with a smooth, bubble-free finish.
Alternatively, you can allow the finish to dry completely and then sand down any bubbles until the surface is smooth and level. Apply a new coat of polyurethane, making sure to thin it with white spirit or water to make it easier to remove bubbles.
How can I remove the brush strokes?
To remove any brush marks left over from applying the polyurethane, you will need to lightly sand the surface with fine-grit sandpaper. Apply even pressure to each area. You can then use a soft cloth to remove any grit and dust created by sanding the polyurethane.
Once the surface has been properly cleaned, you can apply a new coat of polyurethane to the surface with as few brush strokes as possible. Apply multiple thin coats rather than thinner coats as this will reduce problems.
I was born in 1984 and have been working with wood since 2005 and with wood since 2011. Because of my love of woodworking and carpentry, I started woodhappen.com to teach other enthusiasts about finishing and sealing wood, the best tools for woodworking. wood, the different types of wood and everything else related to wood.See my full profile