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Table of Contents
- 1 Understanding Polyurethane
- 2 How Many Coats of Polyurethane Should You Use?
- 3 How to Apply Polyurethane
- 4 Tutorial on Applying Polyurethane
- 5 How to Apply the First Coat
- 6 Wet Sand the First Coat
- 7 How to Apply Subsequent Coats
- 8 Sanding Between Coats of Polyurethane
- 9 Polishing the Surface
- 10 Tips and Tricks When Using Polyurethane
- 11 Frequently Asked Questions
Polyurethane is a type of protective coat used over wood. People love polyurethane because of its high level of durability and attractive shine. Polyurethane is applied as a clear coat to maintain the natural beauty of the wood and protect it against damage from things like water, UV rays, stains, scratches, and so on.
When we talk about polyurethane, we refer to water-based polyurethane and oil-based polyurethane. Oil-based polyurethane contains polyurethane resin. It is also a type of alkyd varnish. The addition of this resin improves the durability of the product. This means that the polyurethane resin enhances the varnish`s ability to resist water and heat.
You also get water-based polyurethane which is less durable. However, water-based polyurethane has low VOC, low odor, easy-to-clean features, and more. Both polyurethanes have several advantages and disadvantages. The type of polyurethane you apply determines the number of coats. The choice of polyurethane always depends on your preferences and the things you want for your project.
This type of varnish consists of a thick consistency that is highly durable when it is cured. It produces high levels of volatile organic compounds (VOC). This varnish requires at least three to four coats for you to get your desired results. It takes a long time to dry. This means that you will be forced to wait for a long time between coats.
You will notice an amber hue finish when the oil-based polyurethane has finally dried. This type of finish tends to add some warmth to the wood. It also leaves a lighter finish on types of woods like oak or birch. Mineral spirits are essential in cleaning any excess residues of polyurethane.
This type of polyurethane is safe to use because it does not emit volatile organic compounds (VOC). It dries very quickly and can automatically level itself. This polyurethane type is the best to work with because it does not emit any strong odors. However, water-based polyurethane tends to lift the grain of the wood.
Is one coat of water-based polyurethane enough? This type of polyurethane requires many coats to create a complete finish on the wood. It requires more coats is because of its watery and thin consistency. Four to five coats will be enough for your wooden surface. This polyurethane changes from milky white to being clear when it finally dries. It is suitable for preserving the natural tone of the wood. It is quite easy to clean and does not need any complicated products. Water and soap will do the trick.
How Many Coats of Polyurethane Should You Use?
This is one of the most asked questions about polyurethane. The surface type determines the number of coats you need. The type of pf polyurethane to be used affects the number of coats to be applied. Moreover, water-based polyurethane requires more coats as compared to oil-based polyurethane. So, always remember that you will need multiple coats of polyurethane to effectively protect your wooden surfaces.
Water-based polyurethane requires more coats because it is a thinner liquid. So, you have to apply at least four to five coats to reach the expected results. On the other hand, oil-based polyurethane only requires three to four coats because it is a thicker liquid.
So, how many coatsof polyurethane to apply? The number of coats required depends on how frequently that surface is used and the type of polyurethane you are working with.
How to Apply Polyurethane
Now we will look at the different methods used in applying polyurethane. You can apply your polyurethane using a spray, brush, or by wiping it on.
This method of application is suitable for those hard-to-reach, awkward and difficult surfaces. You will require at least five to six coats when using this method. This is a result of the thin consistency of the sprayed polyurethane. Spray polyurethane does provide a much more smooth and even finish.
The brush-on method works well on flat surfaces which require thick layers of durable polyurethane. This method makes it easy to cover larger surface areas because the brush can carry a lot of polyurethane. A foam brush is also suitable for this method if you want to avoid bristle marks. How many coats of polyurethane to apply when brushing? Usually two to four coats depending on the scenario.
This application method is suitable for uneven surfaces. You can also use it for contoured surfaces like stair banisters. The wipe-on method works well in places where brushes might leave drips. However, you might need several coats of polyurethane because the consistency will be a little bit thin.
Tutorial on Applying Polyurethane
You must understand the whole process of applying polyurethane before you get started on your wooden surfaces. The following tips will help you in applying polyurethane like a pro:
- VOC levels of polyurethane can be quite harmful, it is advisable to work in a well-ventilated area and make sure there is plenty of air circulation.
- Always work indoors. Working indoors will prevent dust or any other contaminants from getting to your drying polyurethane surfaces.
- Make sure you wear protective clothing. Protective gear includes a respiratory mask and some goggles.
- Make sure you work on flat surfaces. A flat surface enables your polyurethane to automatically level itself.
- Have a bright light in handy: The light will help you in locating surface imperfections, uneven brush masks, and this will give you enough time to correct your mistakes before the polyurethane dries up.
- Prepare your wooden surfaces before you apply your polyurethane. The surface should be completely free from any form of obstructions. For example, anything that will stick to your wet polyurethane can affect the final look of your project.
- Sand the surfaces first. Preparation also includes sanding the surface first. You can start with 110-grit of sandpaper, then move on to a finer grit of 220.
- Use a vacuum that has a soft brush to get rid of dirt. Thoroughly vacuum your surfaces using the attached vacuum soft brush. Make sure you get rid of all dirt and dust, finish the process by wiping the surface from excess oils and residues.
- Wet the wooden surface. The grain will be raised by wetting the surface. You must start with 220-grit sandpaper to smoothen your surfaces. You will use this sandpaper later in your project because water-based polyurethane raises the grain.
Note: Coarse sandpaper tends to leave marks on the surface. You must use a fine grade of sandpaper to get rid of these marks.
Sealing the Surface
- Always apply a sealant when working with porous materials. A sealant will ensure that bubbles do not form. The best way to do this is by thinning your polyurethane, to make it usable as a sealant layer.
- The process of thinning polyurethane is quite easy. Thin your polyurethane using a ratio of 2:1 of oil-based polyurethane to mineral spirits. Mix these two in a jar while stirring occasionally. Water is also effective in diluting water-based polyurethane.
- Applying the sealer with a brush will guarantee the best results. If you want to use a brush, a natural bristled one is the best choice. Dip an inch of the brush into polyurethane. Apply it in long and even strokes. Make sure you get rid of any drips and smoothen them back onto the even surface.
- Applying water–based polyurethane on oil-based stain. Prepare your surface first to enhance better adhesion. Maximize the bonding process by using steel wool to roughen the surface.
How to Apply the First Coat
- Apply the first coat 24 hours after the sealant. Apply the sealant first before you apply your first coat of polyurethane. Once the sealant has dried, you can begin applying your first coat of polyurethane.
- You should not thin the first coat. Thinning the first coat might affect your polyurethane.
- The methods of application are quite different for both polyurethanes. The application process of the two polyurethanes is quite different. So, you must follow the processes below.
- Make sure you make even coats. You can do this by making overlaps with your brush strokes. Always catch any drips before they run any further.
Applying Water-Based Polyurethane
- A foam brush is effective in the process of applying the coats. Do not apply the water-based polyurethane in thick coats. Thick coats will raise the grain. Apply thin coats of water-based polyurethane using a cloth or foam brush.
- There is no need to sand your surface when using this polyurethane. You do not always have to stress yourself with sanding before applying water-based polyurethane. However, you can do it anyway.
- Three coats on surfaces that are not used often are enough. You can use at least four coats on surfaces that are used frequently.
Applying Oil-Based Polyurethane
- Use a brush with natural bristles when applying oil-based polyurethane coats. If you do not have a brush with natural bristles you can opt for a foam brush. Never use cheap brushes or these might leave brush strokes on the surfaces. A foam brush is suitable for flat surfaces while a bristled brush will work well in adding finer details.
- Apply an even coat. Make sure you brush in even coats, not thick or thin coats. Use long, straight strokes brushing from top to bottom. This will cause the bubbles to burst on their own.
- Two or three coats are enough for maximum protection. While you are working on the two or three coats, do not forget to sand between each coat.
Note: Do not wipe a bristled brush on the edge of the can while you are making your coats because this can cause bubbles. However, you can lightly tap the brush on the container to remove any excess polyurethane.
Wet Sand the First Coat
- Wet sand the surface when the first coat of polyurethane has dried. Wet sanding is done to get rid of all blemishes and bumps from the surface. You should do wet sanding at least 24 hours after applying the first coat. You can opt for a sanding block and 400-grit sandpaper.
- You should dip the sandpaper in water. Make sure you dip the sandpaper in water as frequently as you can. Your sandpaper should be saturated properly, as this will prevent the sandpaper from damaging the polyurethane finish. You can start sanding the surface.
- Sand until your surface is smooth. Always ensure that your surface is smooth after sanding. Wipe the surface using a damp cloth, then use a lint-free cloth for drying.
How to Apply Subsequent Coats
- Apply subsequent coats after 24 to 48 hours have passed. Make sure the polyurethane has dried before applying the subsequent coats.
- Sanding between coats is not necessary. Since the product dries quite fast, it will be advisable to remove any dust before applying the next coat of polyurethane. This will prevent uneven surfaces.
- It is not necessary to sand the final coat. The final coat only needs polishing for it to have an attractive finish. When it comes to polyurethane, sanding the final coat is not necessary.
Note: Always apply your polyurethane in the same direction as the grain. Make sure you spread the polyurethane evenly.
Sanding Between Coats of Polyurethane
- Fine-grit sandpaper is the most effective sanding method. Use fine-grit sandpaper when sanding between polyurethane coats. Allow at least 24 to 48 hours of dry time between each coat.
- Thorough sanding is required for glossy finishes. Semi-gloss finishes do not require thorough sanding. Glossy finishes are not capable of hiding imperfections as compared to semi-gloss finishes. Glossy finishes do not have adherence properties, so they need a rough surface to stick well.
- Be cautious when handling a sanding block. When using a sanding block for sanding be extra careful because it might cause clogs, scratches, and so on. These may not show until you apply the next coat.
- Steel wool is also necessary. You can also use steel wool instead of sanding paper, or a synthetic abrasive pad. However, both materials do not work as effectively as sandpaper does. Steel wool often leaves traces of steel.
Polishing the Surface
- The final coat should not be polished. This is important especially after wet sanding the second coat. However, you must allow the polyurethane to dry for at least 48 hours before you start polishing the surface.
- Get a good quality polishing paste. It is always best to get a good quality product. One that will be effective enough in removing scratches that may be left by the sandpaper. An abrasive polishing paste will restore your polyurethane to its original shine.
- Dampen a cotton cloth in water. Use the damp cloth to apply a polishing paste while rubbing it all over the surface. Rub the surface in circular motions.
- Leave the surface to dry. Use a dry cloth to buff the finish after it has fully dried. If you notice some cloudiness on the finish, then apply more of the polishing paste. Buff the surface again until it has reached your expected results.
Tips and Tricks When Using Polyurethane
- Do not shake your can of polyurethane. Shaking the can of polyurethane before use is not necessary because you will create bubbles. Rather gently stir the mixture.
- Oil-based polyurethane requires a good natural bristled brush. A brush with natural bristles is effective when applying oil-based polyurethane. This is because synthetic bristles tend to create air bubbles.
- Water-based polyurethane is effective when applied with synthetic filament brushes. It is advisable to use brushes made from nylon or polyester when applying water-based polyurethane. Rollers and foam brushes can cause bubbles.
- Thinning polyurethane is necessary. It is important to thin polyurethane because this will enhance it to dry faster.
- Do not thin the first coat. The first coat cannot be thinned, but all other coats can be thinned according to your preferences. Thinning the first coat will prevent the polyurethane from sticking to the surface.
- Make sure you use a solvent to keep your brush damp. It will be easier to clean your brush if you dip it into mineral salts or water. This works on both polyurethanes.
- You should avoid wiping your brush against the can of polyurethane. Wiping the brush in this manner can create bubbles. However, you can tap the brush over the can to remove any excess polyurethane.
- Make sure you are applying your polyurethane in the direction of the grain. Work with your polyurethane close to the wood pores. This is because the wood will ensure that you will have an even finish.
- Thinner coatings prevent drippage. Always use thin coats when applying polyurethane. Thin coatings can be achieved by using a spray. If this does not work, you can use a razor to get rid of all the drips.
Frequently Asked Questions
What Temperature Does Polyurethane Dry?
77 degrees Fahrenheit is the best temperature. Polyurethane dries better at this temperature. However, the drying process depends also on humidity and a proper ventilation area. The humidity level should be at least 50% compared to the temperature.
Is it Possible to Get Rid of Brush Marks?
Yes, you can sand your polyurethane surface with fine-grit sandpaper. Always apply even pressure throughout the surface. If there is any sand or dust left after the process of sanding, use a soft cloth to get rid of those. Once you have achieved your desired results, then you can apply another coat of polyurethane. Make sure you use a few brush strokes to avoid making the same mistake.
Is it Possible to Remove Bubbles?
There are two options for dealing with bubbles. A rag dipped in mineral salts can be used to rub the surface for at least 15 to 30 minutes. Make sure you do not disturb the polyurethane surface. Turpentine can also work like mineral spirits. Remove the excess polyurethane by wiping it off, thus leaving a smooth surface free from bubbles.
The other method is to leave the polyurethane surface to dry completely. When the surface has dried, you can sand it down until it is fine and even. You can then proceed to apply a new coat of polyurethane. However, make sure you thin this coat using mineral spirits. Water can also work, and this will ensure that all the bubbles have been completely removed.
How Long Does it Take Polyurethane to Dry?
24 hours is enough for oil-based polyurethane to dry This is because it has a thinner consistency. Water-based polyurethane has a fast drying time when compared to oil-based polyurethane. You can touch water-based polyurethane within six hours of drying. Factors like humidity, thick coats, low temperatures affect the drying time of polyurethane.
In order to know how many coats of polyurethane to apply, you need to understand the product you are working with as well as the wood surface requirements. We hope that our guide above has covered verything you needed to know.