Acrylic paint is a favorite among painters. It adheres well to any surface and does not require a long time to dry. However, acrylic paint tends to be dull and dark once it dries. Additionally, it dries into a soft exterior that easily attracts dust and dirt. Because of this, it is essential to apply a clear finishing coat to protect the paint from harsh elements like high heat & UV rays and keep its color vibrant. But is it safe to use any clear finishing topcoat on acrylic paint? Can you polyurethane over acrylic paint?
Yes, you can use polyurethane to protect acrylic paint, provided you prepare the paint’s surface well. Oil-based and water-based polyurethane will work well to protect your color; however, I recommend sticking to water-based poly because the oil-based products will leave a yellow or amber tint on lighter paints.
In this article, I’m largely going to talk about polyurethane and its interaction with acrylic paint. The information in this piece is detailed and well crafted with the intention of giving you the very best information regarding the subject.
How Do You Apply Polyurethane to Acrylic Paint?
Tip: If you intend to apply polyurethane over a fresh coat of acrylic paint, make sure that the paint cures completely before proceeding.
Step 1: Clean the painted surface.
- Dip a clean rag in warm water and gently wipe away any dust or dirt on the paint.
- If there is grease on the surface, add a mild detergent to the warm water and use the solution to clean the paint. Be careful not to scour too hard when using the water-detergent solution because it could strip some color.
Step 2: Sand the surface lightly.
- Scuff the surface of the paint with 120-grit sandpaper. The goal here is to reduce the sheen of the acrylic paint without leaving deep scratches that may show after applying polyurethane.
- After you finish sanding, wipe off the sanding dust with a damp rag or tack cloth.
Step 3: Apply the first coat.
- Apply the first layer of polyurethane using a brush or sprayer. It is best to avoid rollers because they tend to leave a lot of bubbles that harden into the finish making it look unpolished.
- After putting on the first layer, allow it to dry for the time specified on the manufacturer’s label. Once dry, scuff the polyurethane coat with 120-grit sandpaper to flatten any bubbles present and remove visible brush strokes.
Step 4: Apply the second coat.
- Carefully apply another thin layer of poly over the first to ensure an even better and durable protective coat for the acrylic paint.
- Two coats of polyurethane are enough to gloss up and brighten acrylic paint, so don’t feel pressured to add a third.
How Soon Can You Polyurethane Over Acrylic Paint?
The best time to apply polyurethane over acrylic paint is after the color has fully cured. Acrylic paint dries quicker than most paints, so applying a clear coat on it after 24-48 hours is safe. However, I recommend waiting for 72 hours to ensure that the paint cures completely to ensure the best results.
So, What’s the difference between drying time and curing time?
Most people interchange these two terms using them to refer to paint or surface coatings that feel dry to the touch. However, the two terms differ as follows:
- Drying means that all the solvents in the paint or coating product have evaporated, leaving the surface feeling less tacky. However, the coat is not 100% hardened and can still get dented when you apply pressure.
- Curing means that the paint has reached its maximum hardness and is now invulnerable to the elements and external pressure.
Lightly touch an inconspicuous area on the painted surface to check if your acrylic paint is dry enough for polyurethane application. If it is sticky, wait a bit longer before proceeding. If it doesn’t feel tacky, then the paint is ready to coat.
To check if the paint is cured, press a fingernail into an inconspicuous area on the surface. If it leaves an indent, then the paint hasn’t cured yet.
Note: Applying polyurethane over paint that isn’t dry enough for a clear coat will lead to complications in the future. The application process could smudge the wet paint leaving it ugly. The paint could also bleed into the poly resin tainting its color and reducing the polyurethane’s ability to protect it.
What Is the Difference Between Acrylic and Polyurethane?
Acrylics are products that are suitable for coating light-colored or chemically bleached surfaces. Manufacturers formulated it with colorless resins, providing a transparent protective film over the surfaces they coat.
Acrylic coatings have excellent chemical and mechanical resistance. Their elastic nature allows them to protect surfaces from damages caused by abrasions and other external forces. These products are best suited for application on light-colored surfaces because they are resistant to yellowing.
Acrylics are thin therefore easy to apply. The products emit less toxic fumes during application and curing; hence they are mostly recommended for indoor use. However, these products require constant maintenance to keep the surfaces looking fresh and beautiful.
On the other hand, polyurethanes are much thicker and more durable than acrylics, requiring less maintenance over time. They take longer to apply because you have to let each coat harden enough to scuff to apply another one.
I do not recommend using polyurethane finishes on light-colored or bleached surfaces because they tend to yellow after a while. Additionally, you’ll need extra protection when working with polyurethanes. They emit toxic fumes that are harmful when breathed in, and the chemicals in them can also damage your skin.
So, make sure that your workspace is always a well-ventilated area and wear protective gear to keep yourself from harm when working with polyurethane.
How Do You Prep Polyurethane for Painting?
Step I: Protect Yourself.
- Start by putting on rubber gloves and safety goggles to avoid the exposure of your eyes and skin to splashing and spilling chemicals. Also, put on a face mask to avoid inhaling fumes from the products you’ll use.
- Next, lay down a drop cloth to catch debris and paint spills as you work. Furthermore, ensure that your work area is well ventilated – If you are working indoors, open all the windows and crank up the fans to ensure sufficient air circulation in the room.
Step II: Clean the surface.
It is important to clean the polyurethane surface before coating it with paint. Cleaning the surface first prevents the paint from collecting dust or clumping as you apply it. To clean the poly:
- Combine a ¼ cup of Trisodium Phosphate (TSP) with 1 gallon of water in a bucket to make a cleaning solution. Soak a sponge with a coarse scrubbing surface in the solution, wring out the excess, then wipe the surface of the polyurethane in small circular motions. Doing this will remove any dust, grime, and other residues present on the surface.
- Spread the cleaning solution over areas with stubborn grime and stains, then scrub with a bristled scrubbing brush in circular motions.
Step III: Let the surface dry.
The surface needs to dry completely before proceeding with the next steps. Working on a wet surface will make the work harder, and the surface may retain some sanding dust.
- Use a clean, dry rag to wipe the polyurethane surface and start the drying process. Next, wait for at least 15 minutes for all the water to dry before proceeding.
Step IV: Repair damages.
- Fill any cracks using wood putty to create a smooth and even surface for painting. Apply just enough product to fill the little areas, then let it dry according to the manufacturer’s instructions.
Step V: Sand the polyurethane.
- Use 120-220 grit sandpaper to scuff the polyurethane surface. Work in sections to ensure you sand the area evenly and use small circular motions to avoid going too deep. For larger projects, use an automatic sander to save on time.
- After sanding, use your normal vacuum cleaner to suck up all the sanding dust, then polish the surface with a moist cloth to eliminate any dust left by the vacuum.
Step VI: Prime the Polyurethane coat.
- Use an oil-based primer to prime your surface because it is the most compatible with polyurethane. It adheres well to poly and provides the best coverage. You can go for a foam roller or paintbrush to apply the primer, depending on your preference.
- Let the product dry according to the manufacturer’s label of the product you choose, then coat the area with the paint color and finish of your choice.
How Long Should I Let Polyurethane Dry?
The amount of time that polyurethane requires to dry properly will depend on some factors you should consider as you plan your project. The drying time of the product will vary depending on the type of polyurethane you use, the temperature and moisture levels of the surrounding area, the type of wood, and the method you choose to apply the product.
Below is an explanation of how these factors affect the dry time of polyurethane.
Types of polyurethane.
Oil-based polyurethane takes much longer to dry because they are thicker than their water-based counterparts. Additionally, the oil composition in these products takes a long time to evaporate.
Oil-based poly requires 6-10 hours to dry enough for sanding and a second coat. If you’re protecting floorboards, let the polyurethane dry for a full 2 hours before walking on it. After 24 hours, you can walk safely on the floors with your socks on without leaving dents in the polyurethane coat.
Avoid wearing shoes, walking on bare feet, and keep your pets away from the project during this period. After 48 hours, the coat will be dry enough to withstand pressure from shoes, bare feet, and some furniture.
Even though oil-based poly dries sufficiently within 48 hours, it requires one month to cure completely. So, avoid laying down rugs or any other types of floor covering until the polyurethane dries.
Water-based polyurethane dries much faster than oil-based coats. It is thin, and the water solvent used in its formulation evaporates faster into the air than oil.
These products require about 4-6 hours to dry enough for a second coat and 24 hours for you to be able to walk on the surface with your shoes on. You can move your furniture back in after 8 hours, and in 2 weeks, you can put your carpet back in.
Even though it is safe to put back your floor rugs after two weeks, I recommend waiting for a full 30 days for the paint to cure completely to avoid future complications.
Manufacturers based the polyurethane drying times mentioned above on a standard 70℉. Temperatures higher than that will shorten the drying times because the hot air will evaporate the solvents in the polyurethane faster.
In lower temperatures below 65℉, the polyurethane will take longer to dry because the solvents in the product evaporate slowly. When the temperatures drop below 55℉, the solvents will be too cold to evaporate; hence, the coat will remain sticky until the temperature rises.
Just like temperature, the humidity levels of your work area will also impact the dry time of the product you’re using. Polyurethane will take much longer to dry in areas with high humidity.
The high percentage of moisture in the atmosphere makes it hard for the air to absorb evaporating solvents from the product. High humidity can extend the drying time by as much as 12 hours.
In comparison, low humidity levels cause polyurethane to dry much quicker. Because the air is dry, it sucks moisture faster from the coat. When applying polyurethane in less humid areas, do it quickly and maintain a wet edge to achieve even coats.
- Type of wood.
Manufacturers often forget to include this factor when working out the drying time of their polyurethane products. You should know that some wood species produce chemicals that slow down the drying and curing of poly.
If you are working with aromatic cedar or rosewood, be prepared for some delays in your project. These woods produce so many natural oils that slow down the drying process of polyurethane.
- Method of application.
You can utilize either a spray gun or a paintbrush to apply polyurethane, and each method impacts the dry time of the product in different ways.
Brushes tend to hold more product, so they leave thicker layers that take longer to dry. On the other hand, if you spray on the product, the layers formed will be thinner; hence they will take less time to dry.
Furthermore, special wipe-on polyurethane coatings leave thinner layers compared to the two previous application methods. These products are ideal when working on smaller areas, and they dry even faster.
Is Polyurethane an Acrylic Sealer?
Polyurethane is not an acrylic sealer; however, those two products provide almost similar benefits when used to coat surfaces. Even with similar protective qualities, polyurethane and acrylic sealers differ in formulation, drying time, the number of layers required for maximum protection, etc.
Acrylic sealers are thin filmed coatings that dry fairly quickly, and you can use them to coat surfaces indoors and outdoors. This product provides ample protection against water and chlorine damage; hence, it is perfect for use around swimming pools and other areas constantly exposed to water.
These sealers are formulated either as water or solvent-based and have minimum yellowing properties. Additionally, they come in several sheen levels ranging from matte to high gloss.
On the downside, acrylic sealers wear out fast, so they require constant maintenance or reapplication after 1-3 years. They often become brittle and start to crack as they age, so look out for signs of wear.
In comparison, polyurethanes are thick film coatings that are perfect for use in high-traffic areas. You can use them to coat interior and exterior surfaces, but they take longer to dry than acrylic sealers.
Polyurethanes are more elastic; hence, they resist scratches and dents because their elasticity absorbs some of the impacts. Because of this, they last longer than acrylic sealers.
On the downside, oil-based and cheap water-based polyurethanes tend to leave a yellowing tint on the surfaces they coat
What Kind of Polyurethane do You Use for Cornhole Boards?
You can use either water-based or oil-based poly as the finishing coat for your cornhole board. The product you choose will depend on your understanding of these polyurethane types.
It would be best to use oil-based polyurethane products if you enjoy a regular game of cornhole. This product is durable and will protect your board for much longer. However, oil-based poly will leave your board with a yellow tint, so only use it if you don’t mind this fact.
If you want the grain of the wood you used to make your board to show through the finish, I recommend using water-based polyurethane. This product dries clear and will protect your board for a long time, provided you follow the proper steps when applying it.
I recommend applying up to 5 coats when using oil-based poly and up to 10 coats when using water-based poly to ensure a sturdy protection layer for your board. Apply the product lengthwise along the board’s surface in even brush strokes, and make sure that you sand the layer before the last to provide an even and smooth playing surface.
Can I Use Minwax Polycrylic Over Acrylic Paint?
Yes, you can. Minwax polycrylic is an affordable product that is easy to apply over acrylic paint. You can apply it using a foam roller or a brush, but don’t worry if you are concerned about brush strokes showing in the finish. Minwax polycrylic self-levels, so it spreads and smooths itself out, getting rid of any brush strokes in the process.
Furthermore, Minwax polycrylic dries fast to be ready for a second coat in as little as two hours. It dries into a clear protective film that doesn’t yellow the paint over time and is easy to clean with soap and water. This protective coat is also hard enough to resist damage from scuffing, abrasion, and most household chemicals.
However, to produce the best results, you will have to allow the acrylic paint to cure completely before applying Minwax polycrylic. Letting the paint cure will prevent the solvents in the polycrylic from reacting with the few remaining in the drying coat of paint. As a result, the paint color won’t run, discolor or turn hazy with time.
What Happens If You Don’t Sand Between Coats of Polyurethane?
There is no significant impact on your polyurethane finish if you don’t sand between each coat. The coat will feel a bit rough, and you may also feel tiny bumps when you run your hand over it, but there is no visual difference between scuffed and unscuffed layers.
However, I still recommend sanding each coat before applying the next one to improve adhesion between layers and provide a leveled finish.
How Can I Make Polyurethane Dry Faster?
One of the biggest challenges that woodworkers face when working with polyurethane is the long wait to dry and cure the finish. Waiting for the product to dry naturally is the best thing to do; however, you can use any of the methods below to speed up the process if you are short on time.
- Thin the polyurethane.
Thinning polyurethane is one of the best ways to make it dry faster. The best thinning product to use for this is mineral spirits. Mineral spirits evaporate more quickly than most thinning agents, and they have no varnish-thinner ratio restrictions. You can thin your polyurethane with up to 50% mineral spirits to create a wipe-on clear coat that is easy to spread and dries faster.
- Increase the temperature in your work area.
Since temperature affects the drying time of polyurethane, you can increase the temperature in your workspace to speed up the process. You can use a space heater or a heat lamp to make the air in your space hotter or use a blow drier to hasten the drying of poly applied to smaller surfaces.
- Lower the humidity of your workspace.
Less moisture in the atmosphere reduces the dry time of polyurethane significantly. So, if you are working in a humid area, you can use a dehumidifier to suck up the moisture ensuring a less humid workspace for your clear coat to dry faster.
Can You Put Too Many Coats of Polyurethane?
I do not recommend applying more than three coats of polyurethane finish on your wood because the extra layers have no added benefit on your surface. The extra coats will only increase the cost of applying the finish, and it will extend the drying timeline of the product by as much as 24 hours.
Applying many coats of polyurethane will also make the finish too thick, gloppy, and more prone to peeling in the future. Furthermore, too many layers of polyurethane provide a more amber tint than usual, especially when using oil-based products or cheap water-based polyurethanes.
Why Is the Polyurethane Not Drying?
You need to develop some patience when working with polyurethane to give it ample time to dry. However, sometimes the polyurethane remains sticky even after the recommended drying time has elapsed. What could be the cause of this?
External factors cause the prolonged drying time of poly rather than the condition of the product itself.
There are four main reasons why polyurethane may struggle to dry. These are:
- Natural oils in the wood.
Some wood species such as rosewood and aromatic cedar contain a natural resin comprised mainly of oil. So, when you apply polyurethane to the bare wood, the solvents in the finish will mix with the oily resin in the wood affecting the dry time of the polyurethane.
- Work area conditions
The atmospheric condition of the area you’re working in also plays a major role in drying polyurethane. If your space is highly humid with low temperatures, the finishing formula will take longer than expected to dry. In this case, I recommend waiting a bit longer for the product to dry properly, but if you don’t have much time, use the methods mentioned in this article to make polyurethane dry faster.
- Applying thick layers.
Slapping on thick layers of polyurethane on your surface will surely impact how long each coat takes to dry. You may argue that thicker layers protect the surface better, which may be true; however, the thick layers will take much longer to dry.
Ideally, it is best to apply each coat thinly using a natural bristle brush or a spray gun. Instead of laying it on thick, apply several thin coats to ensure that each coat and the overall finish dries properly and fast.
- Lack of ventilation.
After applying polyurethane, it is important to let it dry in a space with good air movement. If the project is indoors, crack open a window and let the fan run slow to increase ventilation allowing each coat to dry faster.
Can You Let Polyurethane Dry In the Sun?
You can let polyurethane dry in the sun; however, this isn’t the best condition because poly finishes are highly vulnerable to UV damage from direct sunlight. Additionally, direct sunlight may cause the poly to dry faster, but it also increases the chances of the coat cracking sooner.
If your only choice is to let your surface dry outside in the sun, be sure to check the label on the package to know the best temperature ranges that produce great results.
Also, ensure that the first coat cures fully before applying the second coat to avoid pinholes in the final coat. These pinholes are caused by the poly in the first coat releasing gases as it cures. The gases get trapped under the second coat and cause bubbles to form. Additionally, the bubbles on the outer layer may pop, leaving the polyurethane surface with little craters.
Tip: If you are working outside and the sun is too hot, try and control the climate of the work area. Put up a sunshade to keep off direct sunlight and allow the finish to dry in conditions close to normal.
What Is the Best Temperature for Polyurethane to Dry?
The optimum temperature for polyurethane to dry and cure properly is 70℉. If you let the finishing dry in temperatures higher than 70℉, you increase the risk of bubbles forming and the coat cracking from drying too fast.
In comparison, in temperatures below 70℉, polyurethane will take much longer to dry. When the conditions become too cold, the finishing will not dry hence stalling your project.
Will a Fan Speed Up Polyurethane Drying Time?
Using a fan when working indoors will amp up the ventilation, and as a result, the polyurethane will dry a bit faster than those applied in a room without proper air circulation. The fan will push out all the air saturated with evaporated solvents from the polyurethane, allowing fresh unsaturated air to flow. The unsaturated air will suck up more of the solvent then get pushed out by the fan, continuing the cycle.
Furthermore, proper air circulation will ensure that you aren’t exposed to harsh product fumes, especially when using oil-based polyurethane.
While fans are an excellent way of improving the ventilation in a room, keep in mind that they can easily stir up dirt and dust, which may end up on the wet polyurethane surface, ruining your finish.
Can I Apply Polyurethane In High Humidity?
I do not recommend applying polyurethane in high humidity because highly humid atmospheres contain a lot of moisture in the air. The moisture can settle on your surface, causing it to become damp as you apply the varnish.
It is important to apply polyurethane on a dry surface so that it sticks to the material without developing water bubblers under the coat.
The optimum humidity levels for applying polyurethane are between 45%-55%. Oil-based polyurethane is more tolerant to the elements and safe to apply even when humidity levels reach 70%. However, remember that high humidity levels mean that your finish will take longer to dry.
Polyurethane is one of the most preferred clear coatings used to protect wooden surfaces. It is a durable product that dries into a sturdy coat resistant to harsh weather elements and strong chemicals. However, it is common to see surfaces coated with polyurethane turning yellow or amber with time.
Some paints like acrylic paint often require one or two layers of clear finishing coats to keep their color vibrant and prevent the product from stripping and chipping. Because of this, several people ask…
Can You Polyurethane Over Acrylic Paint?
Yes, you can apply polyurethane over acrylic paint, provided that you let the paint cure completely and you prepare the surface properly. Proper surface preparation is the key to your project looking well polished after all the products cure.