You might be wondering if it’s a good idea to mix polyurethane and epoxy. Will these two chemicals be able to bond together? Are there any adverse reactions if you choose to put polyurethane over epoxy?
You can put polyurethane over epoxy. Polyurethane is a sealant and makes your project shine. However, ensure that the type of polyurethane you use, whether oil- or water-based, is suited for your project and will be able to bond with the material used. Furthermore, don’t put epoxy over polyurethane.
To learn more about why you should put polyurethane over epoxy and the properties of these resins, keep reading!
Is It Safe To Put Polyurethane Over Epoxy?
It is safe to put polyurethane over epoxy. Using epoxy on your project ensures that it is moisture-resistant, protecting the material from wear and tear. Adding polyurethane finish over epoxy will keep your project safe from UV rays and scratches.
Epoxy is a resin that is commonly used for woodworking projects. It is a robust and versatile material that is highly moisture-resistant, making it perfect for outdoor use.
It is also used to bond various materials, including metals and plastics.
Unlike polyurethane, epoxy only has one finished form – a hardened state acting as a sealant. However, polyurethane is much more flexible than epoxy. It can exist in various forms once cured, even being used in foams and rubbers.
For example, most people choose to add a polyurethane coating over epoxy for their wooden floors. The epoxy attaches itself to the wood and prevents it from changing dimensions due to the absorption or loss of moisture. The added polyurethane coating prevents oxidation of the varnish due to exposure to the sun’s UV rays and extends the life of the epoxy barrier.
In addition to this, the added coating of polyurethane will increase the number of layers to the floor coating and allow it to absorb impacts better.
You may also like: Can You Put Polyurethane Over Paint?
Can You Put Water-Based Polyurethane Over Epoxy?
Water-based polyurethane can be put over epoxy. However, consider using an oil-based polyurethane instead of a water-based one that might not coat properly. Ensure that the epoxy is sanded correctly before applying polyurethane for a glossy finish.
Sanding the epoxy is necessary before adding your polyurethane finish because it simultaneously removes imperfections while creating adhesion so that chemical bonds can form between the polyurethane and epoxy.
However, using improper sanding techniques can result in scratch marks which will be visible through your polyurethane finish if it is clear.
If you don’t already have sandpaper, consider purchasing high grit sandpaper like this LotFancy 320 Grit Wet Dry Sandpaper from Amazon. These sandpaper sheets are affordable and easy to use.
Remember that you will likely need many different grits of sandpaper for the sanding process to get a smooth and even surface.
Before adding your polyurethane coat, you should remove the blush off of the cleared epoxy first. This can be done with some laundry detergent. You should avoid using soap as it contains waxes that stick to the epoxy and interfere with a good finish.
If you’re worried about the clarity of your epoxy after applying your polyurethane, you should do a test with some water-based polyurethane. Non-water-based polyurethanes frequently have a yellow or amber tint to them, so consider the possibility of coloring before you use polyurethane over an epoxy.
Can You Put Epoxy Over Polyurethane?
You can put epoxy over polyurethane, but it’s not a good idea. As epoxy has no UV resistance, it will degenerate quickly after you put it on top of the varnish. It will turn white and flake off quickly. Plus, putting epoxy over water-based polyurethane will cause it to soften.
In addition to this, if you are putting epoxy over water-based polyurethane, you will end up with various problems. Imperfections like fisheyes will form on the surface, and the epoxy could push against the polyurethane and cause it to wrinkle.
Traditionally, epoxy goes before whichever varnish you want to use. This gives it a more stable base for the varnish than the project’s material, especially if it is wood. As a result, you eventually need fewer coats of varnish to get the characteristic glossy look many people want.
If the varnish has been applied improperly or is coming off, try the following.
- Sand down the material until the varnish comes off.
- Add a few coats of epoxy.
- Add the varnish again.
Doing things in this order also means that you have to use fewer coats of epoxy to achieve the results you want.
However, if you have purchased a product built entirely of polyurethane and are facing some issues with it, like a table or flooring, it might be a good idea to use an epoxy finish.
Before using your finish, ensure that the polyurethane is completely cured.
Here’s what you should do in those instances:
- Prepare the surface. Epoxy is notorious for sticking to anything and everything, including dust. Ensure that the surface is clean and sand it thoroughly to retain any varnish.
- Know your material. You should know how well the material you are using retains heat. For example, if you’re using wood, it is a good insulator of heat, so you should not be using chilly epoxy as it could make the wood expand.
- Apply the epoxy coat. You should apply the epoxy coat using the roll and tip method illustrated in the video below.
- Apply your next coat only after the first coat becomes tacky. You should apply anywhere from two to four coats to ensure a smooth finish.
Epoxy and polyurethane bond very well together, so you can combine them. However, be sure to put polyurethane over epoxy and not the other way around.
Before putting your finish over the entire surface, always be sure to test it out on a few small pieces. This way, if the two materials react badly due to improper technique, like curing time, or the presence of paint, you can easily correct your mistake.