Using polyurethane finish to seal wood has become quite common as many people try to protect their impressive wooden projects from damage. UV light rays, moisture, and heat, among many other factors, can cause wood to degrade. Polyurethane is a sure-fire way to prevent this from happening or at least prolong its life span.
Polyurethane comes in both water-based and oil-based forms. Their application varies, but one thing remains constant; they all require a proper application for this sealer to work effectively. Polyurethane is used to cover wooden surfaces. It acts as a smooth finish and sealant, preventing damage and importing the shine of the wood.
The part polyurethane plays in protecting wood is clear; however, improper application will severely reduce its effectiveness. There are several ways to apply polyurethane finish to your wood. However, no matter which way you choose, you can still make mistakes. These mistakes will make the finish less effective and unappealing.
Polyurethane mistakes can be corrected if done right. This guide seeks to identify and proffer solutions to common mistakes people make when applying polyurethane finish.
Polyurethane Mistakes And How to Fix Them?
You can fix some polyurethane mistakes by sanding, while others can be fixed without sanding the wood. Here is a comprehensive list of possible mistakes you may encounter when applying this finish and how to remedy each mistake.
1. Cloudy Finish
When you apply polyurethane to your wooden surface, it is supposed to be clear and shiny when it cures, however, this is not always the case. Sometimes you see a dull and cloudy look when the polyurethane dries out.
One of the main causes of a cloudy look is the zinc oxide added by manufacturers to act as a flattening agent. When zinc collects under the can, it is not evenly distributed and is heavily concentrated in one area. This causes the look to be cloudy and dull. To prevent this problem, stir the contents to mix everything before application.
Storing the can in extreme weather conditions can also cause a cloudy finish. To fix the issue of cloudy finish, allow the finish to dry properly. This can take anything from some hours to over 24 hours. You can also soak a cloth with mineral spirits and wipe the surface of the finish several times. Lightly sanding the surface with 200-grit sandpaper can also clear cloudy polyurethane finishes.
2. Uneven Finish
The cause of an uneven polyurethane finish after it has dried is often straightforward and can be attributed to either poor application method or technique. Over laps while trying to cover the full area can cause a double layer in one area and a single layer in the other areas resulting in an uneven finish.
To fix this issue, use sandpaper to sand the higher surface down to the other level before lightly sanding all the surfaces and then finally applying a soft polyurethane coating.
3. Streaks on Finished Surface
Streaks on the surface are identified by faint lines in the direction of application. Streaks are mostly caused by the coarse bristles of the application brush. Trying to overwork the polyurethane onto the wood surface can leave streak marks. To fix the problem, lightly sand the whole area to remove the streaks and then apply a soft coating of polyurethane to the surface.
To prevent this problem, use the right application materials for the type of polyurethane you’re using. Use a quality synthetic brush for water-based polyurethane and a natural bristle brush for oil-based polyurethane. Also, ensure you work the finish gently without forcing it in.
4. Cracked Finish
Sometimes after polyurethane has dried on your wood, you’ll notice that the surface is cracked or crazed. Cleaning the surface with steel wool soaked in mineral spirits and allowing it to dry is the first step. Remove and reapply the polyurethane to complete the process.
5. Puddles
Puddles appear where the application is not uniform across the surface, with some areas seeing more polyurethane. Not allowing the previous layer dry before applying the next polyurethane layer can easily cause puddles.
Fix the problem by wiping the puddle with a damp cloth if dealing with water-based polyurethane within the first 5 to 10 minutes of application. Use a cloth soaked in mineral spirit to wipe the puddled area not later than 20 minutes for oil-based.
This period is before the polyurethane dries properly. However, if you didn’t notice this before the surface dries, you’ll need to sand lightly and then reapply.
6. Bubbles
Similar to puddles in nature but with different causes, bubbles appear when air pockets are trapped under the polyurethane layer. Shaking the can before the application can trap air inside the polyurethane. Air bubbles trapped between the bristles of the brush and even on the wood surface can cause bubbles. The wrong brush type for the type of polyurethane can cause bubbles.
To fix the problem, do not shake the can. Rather, stir the contents properly. Also, ensure to select the correct brush type for the type of application and type of polyurethane. Clean the surface properly with mineral spirits and alcohol if you’ll be using oil-based and water-based polyurethane, respectively.
Thick coats make it easy for bubbles to be trapped underneath them. Using thin coats will remove any bubbles beforehand. Tapping the top of the bubbles before it dries will flatten them. If you notice the bubbles after it has dried, you may have to sand them and then reapply them.
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7. Peeling Finish
If your dried polyurethane finish is peeling off, oftentimes, there has been a mistake in its application. The peeled-off finish leaves patches exposed and unappealing. Applying thick layers can be the cause of the finish peeling off.
Other times it may be caused by not sanding between layers. Or not cleaning the wood surface of oil and dirt, which prevents the polyurethane from properly sticking to the wood.
To fix this, apply a paint stripper to soften the polyurethane before completely scraping it off. Sand the wood, clean it, and then reapply thin layers while ensuring to sand each layer before the next.
8. Orange Peel Effect
The orange peel effect on polyurethane finished surfaces can be identified by a thick and rough finish like the back of an orange peel. Typically, polyurethane finished surfaces are smooth and clear, but some mistakes can create what is termed the orange peel effect. It is caused when the finish dries faster than it levels and usually occurs when the application is made in cold weather.
Doing the application under normal weather conditions is a good way to prevent this. To fix the problem, you’ll need to sand the surface of the finish before applying again. You can thin the polyurethane by adding mineral spirits or water, depending on the type used.
9. Blushed Finish
Blushing, as it is called, is a situation where water enters the finish. Thus, causing it to have a light milky color as against the clear and woody color it should have. This can occur if you do not sand the surface properly, leaving water on the surface that later seeps into the finish. High humidity and incompatible stain-polyurethane combo can cause blushed surfaces.
To fix the problem, wet a cloth with alcohol, and let it evaporate before gently wiping the surface. Do this several times till the blush disappears. You can also make use of 180-grit sandpaper for tougher blushes before reapplying a thin layer.
10. Discoloration
Sometimes the finished surface presents discolored patches. These patches are usually yellow. This is more of a natural phenomenon rather than a mistake and occurs over time as the polyurethane finish gets older. Natural causes aside, the look is unappealing and makes the wood look abandoned. The major causes for this discoloration include moisture, oil-based finishes, and UV light, among others.
Prevention of this discoloration can be achieved by using water-based polyurethane as they do not turn yellow over time. To fix this issue of discoloration, you will need to sand the surface and reapply a thin layer of polyurethane.
11. Scratches
Finished polyurethane surfaces can have scratches immediately after application and over time. Scratches immediately after application can be caused by sandpaper. These types are usually light. Scratches can also appear sometime after application caused by other factors like a sharp object dragged across the surface.
You can fix the light scratches by using finer sandpaper to smoothen the surface before reapplying a thin polyurethane layer. You can use finer sandpapers up to 320-grit and then apply wax or polish to the surface. For deeper scratches, smoothen the scratch with 0000 steel wool dipped in mineral spirits, wipe with a cloth and allow to dry. Reapply several layers of thin polyurethane and then finish with polish.
12. Cratering
Craters are circular dents that may occur on polyurethane finished surfaces. They are caused when surfaces are not properly cleaned before polyurethane is applied, thereby trapping sand, dust, and chemicals underneath.
All you need is 220-grit sandpaper and rage to fix this problem. Clean the wood surface properly with the rage before applying thin layers of the polyurethane finish. Use the sandpaper to lightly sand the area till you’ve removed the dirt or completely removed the finish, whichever one comes first.
13. Trapped Insect
Insects can be trapped inside the polyurethane finish. Insects can come flying in when you’re applying your finish and get trapped underneath. Sometimes they can even land on the drying surface and get stuck.
The trapped Insect problem can be fixed by removing the trapped insect with something like a toothpick and then applying a thin polyurethane layer. This method is possible when the polyurethane is still wet. For dry polyurethane, sand the surface and remove the insect before reapplying thin layers of the finish.
14. Runs
One of the most common polyurethane mistakes you’ll encounter is the runs where the finish runs before drying, thereby creating long marks across the surface. Runs are especially pronounced when coating vertical surfaces and where drying is low.
To prevent this problem, apply thin layers and put the wood in a horizontal position where possible. To fix the problem, check for runs during application and wipe the excess off with your brush. If you notice the run after it has dried, lightly sand the area and reapply a thin layer of polyurethane.
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Summary
Polyurethane will continue to be that effective finish for your wood as long as you apply it correctly. However, even more experienced woodworkers make mistakes during application which causes problems. These problems can be fixed easily by following laid down guides like this.
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