Polyurethane is a polymer composed of organic units and is one of the best wood finishes available today. Polyurethane finish comes in two forms: oil-based and water-based polyurethane.
Polyurethane finish gives your wood countertop a lasting glossy look. It also enhances its lifespan, protecting your countertop from water, heat, wear, and tear. However, the finishing quality depends on the type of polyurethane you’re working with and the number of coatings you apply.
So, how many coats of polyurethane would be suitable for your wood countertop?
How Many Coats of Polyurethane Should You Use on Wood Countertops?
To get a nice finish on a wooden countertop, apply at least two coatings of oil-based polyurethane. If you’re using water-based polyurethane, 4 or 5 coatings will give a lasting and excellent finish.
Some people try to economize resources by using one layer of coating. However, that would be a waste because a single layer of oil- or water-based coating won’t last long. It will also not give the desired effect.
Now, let’s consider the two types of polyurethane, their make-up, pros, and cons.
Oil-Based Polyurethane
Oil-based polyurethane has been in use long before the introduction of water-based polyurethane. It comprises a mixture of polyurethane resin and alkyd. Oil-based polyurethane is highly toxic and gives off a terrible odor. So, when applying it, ensure you put on a respirator.
Remove children and pets from the place where you’ll be working to avoid allergies or side effects. Also, ensure that the area has sufficient ventilation.
Because it’s very thick, it takes a longer time to cure and dry. So, don’t hope to use that countertop anytime soon.
A helpful tip: Before applying, make sure the area is free from bugs that may fall on it while drying.
Pros of Oil-Based Polyurethane:
- It is more long-lasting and durable than water-based polyurethane. When fully cured, it can withstand any condition and it is not easily damaged.
- It gives off a slight amber-light hue after coating, which gives the wood a kind of warmth and beauty.
- It soaks deeper into the wood to increase its durability.
Cons of Oil-Based Polyurethane:
- It gives off a nasty odor.
- In addition, it takes a longer time to cure and dry.
- To clean it, you’ll need chemicals such as mineral spirit or turpentine. Many people don’t always have this at home.
- It’s very harsh on the health and the environment.
Water-Based Polyurethane
Although it was recently introduced, water-based polyurethane has proven to be a good option for wood finishing.
It comprises polyurethane resin and acrylic resin. This mixture is lighter than oil-based polyurethane, so its layers aren’t as thick as oil-based polyurethane. However, it’s equally as good.
Pros of Water-Based Polyurethane
- Due to its lightness, it dries off quickly, unlike oil-based polyurethane.
- It gives off less VOC, so the odor is minimized.
- It’s easy to clean. Warm water and mild soap will do.
- It’s both health and environment friendly.
- It’s relatively less toxic.
- It finishes off with a clean look.
Cons of Water-Based Polyurethane
- It doesn’t soak into the wood.
- It’s less resistant to heat.
- It reacts when applied over some wood stains.
- It raises wood grains.
Polyurethane Drying And Curing Time
Oil-Based Polyurethane:
A layer of oil-based polyurethane takes 24 hours to be dry enough for sanding. Clean properly after sanding, and then, you can apply another layer. It will be dry to touch after 48 hours. It will take at least four days before you can place anything on it. Complete curing will take at least one month.
Water-Based Polyurethane:
A layer of water-based polyurethane takes at least 8 hours to be dry enough for sanding. Sand properly and clean before adding another layer. It will be dry enough to touch after 24 hours. After two days, you can start placing things on it. Complete curing will take at least 20 days.
Note: Don’t place rubber mats on it till after 30 days to avoid marks on the surface.
Common Mistakes When Coating With Polyurethane
Some mistakes may occur when applying polyurethane. These mistakes can spoil your work.
The following are the mistakes that may occur, their causes, and possible solutions:
Bubbles in the polyurethane finish:
After working, you may find trapped bubbles in your polyurethane finish.
Possible causes include improper cleaning of the surface of the wood and brush, shaking the can of polyurethane before use, cleaning the brush on the side of the polyurethane can, or not using the right brush type for the work.
Preventive measures:
- Clean the brush and the surface of the wood properly before applying polyurethane.
- If it’s an oil-based polyurethane, use a cloth dipped in mineral oil to wipe the surface. If it’s a water-based polyurethane, dip the cloth in alcohol, and use it to wipe the surface.
- For the brush, soak it in solvent to remove air bubbles.
- Instead of shaking the can of polyurethane, stir it slightly to mix uniformly, and it won’t trap any air bubbles inside.
- It is better to use thin coats instead of thick coats because they allow air bubbles to arise during application.
Solution: If you notice any bubbles when coating, gently tap it with your brush tip. However, you can only do this when it’s not yet dry. When dry, you’ll need to sand it.
Holes in the finish (cratering):
Cratering is caused by the silicon in dust and chemicals that fall on the coating.
Solution: You need to lightly sand the top, clean with a cloth, and apply another thin layer of polyurethane. Leave to dry. The bubbles will be gone when it dies.
Scratches in polyurethane finish:
Scratches can come from rough sanding or heavy usage of the surface.
Solutions:
- You’ll have to identify the scratches to determine if it is deep or shallow. Either way, you will have to sand the entire surface and polish it again with polyurethane.
- After identifying the scratches, sand the surface lightly using fine-grit sandpaper, clean the surface properly, and then, using a soft brush, apply polyurethane again.
Puddles in the finish:
Puddles occur when you use a thick layer. They are prone to making puddle marks because it’s almost impossible to do an even thick layer over the surface. As a result, some places will be. Also, not allowing the surface to dry completely before applying the next layer can cause puddles.
Solutions:
- Wipe an oil-based polyurethane surface with a cloth dipped in mineral oil before 20 minutes if it’s water-based, clean with a damp cloth in less than 10 minutes.
- If you can’t clean the surface before it dries off, you’ll need to sand it. But, first, smooth the whole surface, and reapply the coating once again. This time, leave it to dry properly before applying the next layer.
Rough surface:
Possible causes of a rough surface include contaminated polyurethane and not cleaning or sanding the surface properly before applying polyurethane.
Solutions:
- Clear off and screen the finish well for that glossiness to resurface.
- Clean the surface properly before applying polyurethane to avoid dust, sand, and other unwanted particles from sticking around.
- Use fine-grit sandpaper and sand the surface lightly and adequately.
Note: If these solutions prove ineffective, you will have to sand the entire surface and start all over again.
Orange peel effect:
This effect occurs when you use a not properly napped roller instead of a brush or a rag. It can also happen if the temperature is low.
Solutions:
- Keep the temperature at an average level when coating.
- Do not use a roller, especially if you are inexperienced.
- You’ll have to sand the entire surface and start all over again.
Streaking:
Streaks are brush marks on your finish. It causes uneven glossiness. Possible causes include improperly mixed polyurethane, dry brush edge, rough spreading, and excess brush freedom.
Solution: Screen the surface and then apply a new layer of polyurethane—sand before using it again.
Alligatoring:
It appears as cracks and an ugly texture on your finished work. Causes are low-quality polyurethane, too much moisture in the wood, thick coats, and not properly removing the skins on the cracks before filling it up again.
Solution: Screen the surface and sand before adding another layer.
Trapped in bugs and dust:
Bugs or particles can fall on the surface of your finish.
Solutions: If the surface is still wet, use a toothpick or broomstick to remove it. Then apply a little polyurethane at that spot, or leave it like that. It will form by itself.
However, if the surface is almost dry, allow it to dry and remove the insect. Use grit-sand paper and do a dry sanding. Apply polyurethane on the area and leave to dry completely.
Separating issues:
This effect occurs when your polyurethane coating begins to separate over time. Causes of this are contaminated or unevenly mixed polyurethane, the wood may be oily and not bond well with the polyurethane, and the presence of dirt on the surface.
Solutions: The only solution is to sand the entire surface and start coating all over again. This time around, use a new polyurethane finish from a different manufacturer.
Conclusion
The number of coatings you’ll need to have a glossy finish on your wood countertop will depend on the type of polyurethane finish you’re using in your work. There are two types of polyurethane finish: oil-based polyurethane and water-based polyurethane.
If you’re working with oil-based polyurethane, two to three layers of coating will be enough. However, with water-based polyurethane, you’ll need at least coatings.
Oil-based polyurethane lasts longer than water-based based polyurethane. However, it gives off an offensive odor and is toxic. For your safety, use a respirator when working with it.
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