Last Updated on August 27, 2023 by Ernest Godia
If the thought of adding a coat of polyurethane to acrylic paint has crossed your mind, you may be onto something. Applying polyurethane over paint isn’t ludicrous as it might sound. Irrespective of the protection acrylic paint offers wood, it still lacks waterproofing capabilities.
Bare wood is susceptible to rot, decay, insect infestation, and damage by harsh weather elements.
A coat of acrylic paint extends its longevity. However, the paint affects its natural appeal and doesn’t make wood water resistant. A sealer like polyurethane gives the paint a glossy sheen, protects the wood against moisture damage, and prevents the yellow discoloration that characterizes acrylic paints.
In this post, we detail how to apply polyurethane over acrylic paint and highlight several pointers to make the paint job seem professionally done. Read on!
Can I Put Polyurethane Over Acrylic Paint?
Yes. Applying polyurethane over acrylic paint on wood is a creative way to kill two birds with one stone. First, the sealer (polyurethane) protects the wood against water and moisture damage. Secondly, acrylic paints are prone to acquiring a yellowish discoloration over time, and polyurethane helps prevent Support Induced Discoloration (SID).
For excellent results, ensure the paint is dry and cured, and check whether you are using water or oil-based polyurethane.
What is Acrylic Paint?
Acrylic paint comprises pigment suspended in acrylic polymer emulsion and plasticizers, metal soaps, silicon oils, defoamers, or stabilizers.
The paint is known for its versatility; depending on the amount of water or acrylic gel you add, the finish can resemble a gouache, oil paint, or watercolor. Acrylic paint is fast-drying, making it popular among woodworkers, artists, DIYers, and crafters.
Acrylic paint is more elastic than latex paint and more durable with a degree of moisture resistance, but not waterproof.
The paint is suitable for exterior surfaces due to its elasticity, and when mixed with binders, fillers, pigments, and water, you can apply it on indoor surfaces.
Acrylic paint typically costs more than latex paint and requires more preparation. The paint is also more challenging to wash off with soap and warm water than latex paint and requires a cleaning agent.
What is Polyurethane?
Polyurethane is a synthetic polymer resin used as a coating or protective finish for materials like wood. It protects the surface against moisture and other weather elements, enhancing the wood’s durability and appearance.
It is created through a chemical reaction between polyols (a type of alcohol) and diisocyanates (a compound containing reactive functional groups). This reaction results in the formation of a polymeric material with various properties.
Polyurethane offers several advantages as a wood finish, including excellent durability, moisture resistance, chemical resistance, and UV protection. It forms a hard and protective layer on the wood surface, guarding against scratches, wear, and damage.
Polyurethane is valued for its versatility, durability, and protective properties, making it a popular choice for finishing wood surfaces in commercial and residential applications.
Polyurethane finishes can be oil-based or water-based. They are typically available in different sheen levels, such as glossy, satin, or matte, allowing for customization based on desired aesthetics.
Read our detailed comparison of water-based polyurethane versus oil-based polyurethane to see which form suits your needs best.
How to Apply Polyurethane Over Acrylic Paint
You will need the following supplies to apply polyurethane over acrylic paint.
Tools and supplies
- Drop cloth
- Tack rag
- Sandpaper
- Paintbrush, rag, or spray gun
- Protective gear
Procedure for applying polyurethane over acrylic paint
Once you have all the tools and materials for this job, follow the steps below to complete the task.
STEP 1: Ready your workspace
Put on your protective gear to avoid getting polyurethane on your skin and eyes.
Cover your work area with a drop cloth to keep the sealer from dripping, splashing, or spilling on your floors, messing them up. Also, consider taping off the edges or areas you don’t want the sealer.
STEP 2: Clean the surface
Clean the painted surface with a damp rag to remove dirt and debris. If the surface is greasy, use a degreaser or a solvent like trisodium phosphate (TP) when working on an older painted surface. You can also use mineral spirits if the surface has wax.
Avoid using a latex remover as it discolors the existing paint or harsh soaps because they damage the texture of the acrylic paint.
STEP 3: Lightly sand the surface
After the surface is completely dry, gently sand it with 220-grit sandpaper to smooth out any imperfections, paint drips, and stains. Sanding gives the surface texture to which polyurethane adheres.
If the surface needs scuffing, you can go in with 120-grit sandpaper but be careful not to damage the existing paint.
STEP 4: Remove the sanding dust
Wipe off the sanding dust with a tack cloth or a lint-free rag dampened with mineral spirits. Alternatively, you can vacuum or blast the dust with air.
STEP 5: Apply the first coat of polyurethane
Apply the first coat of polyurethane with an applicator of your choice; it could be a foam brush, paintbrush, rag, or spray gun.
A good quality brush is the better choice when applying water-based polyurethane. If you use a brush, open the polyurethane can gently, and don’t shake it. Shaking creates more air bubbles. Apply thin and even coats in one direction for a smooth finish.
Spraying is the better option for a big project with a wise surface to cover. If you use a spray can or sprayer, apply the polyurethane in sweeping motions. Keep a constant distance and pressure to attain a perfect finish.
STEP 6: Let it dry
Let the first coat dry under moderate temperature and humidity conditions. The drying time depends on whether you are using water- or oil-based polyurethane, but 4-6 hours is good enough. Read the manufacturer’s instructions product-specific instructions on this.
STEP7: Sand and wipe the dust
Lightly sand the polyurethane with fine-grit sandpaper to remove brush marks and dust dots. Polyurethane tends to bubble, so sanding the surface will help you knock the bubbles and smooth the surface.
Sanding also helps promote the adhesion of your polyurethane coats. Here is what happens if you do not sand between coats of polyurethane.
Once you are done sanding, ensure you tack away the sanding dust or clean away the particles with a vacuum.
STEP 8: Apply the second coat of poly
Apply a thin second coat of polyurethane and let it dry.
STEP 9: Repeat the steps if you need a third coat
Two coats of polyurethane are usually enough to achieve the desired protection and coverage. However, you may decide your surface could use another coat of poly, and that’s okay. Give the layers ample drying time and lightly sand in between the coats.
STEP 10: Let it dry thoroughly
Keep the painted piece out of reach of children and pets to allow it enough time to dry. Do not use it until the polyurethane surface has fully dried according to the manufacturer’s instructions.
What Types of Polyurethane to Put Over Acrylic Paint?
You can get polyurethane in liquid or aerosol form, so choose the suitable one for your project. Polyurethane is available in two main types, namely:
- Oil-based polyurethane
Oil-based polyurethane gives surfaces a silky smooth finish and a slight golden glow. It is durable and gives better protection against the elements and heat. Oil-based polyurethane is the better pick when coating outdoor acrylic-painted surfaces.
The downside to using oil-based polyurethane is that it contains higher levels of volatile organic compounds (VOCs), making it more toxic.
It has a strong odor, so wearing a respirator mask is recommended when using this type of polyurethane.
Oil-based polyurethane also takes longer to dry, leaving a whitish color over darker acrylic paints. It also dries with a yellowish hue that slightly alters the underlying acrylic paint’s shade.
- Water-based polyurethane
Applying water-based polyurethane over acrylic paint is more popular among woodworkers as it poses fewer challenges than oil-based polyurethane.
Water-based polyurethane is also as durable but less toxic than its oil-based cousin. It boasts low levels of VOCs, making it eco-friendly and less harmful to your health.
The water-based polyurethane coating is a tad bit harder, but it doesn’t acquire a yellow hue with time.
It is also better when sealing brighter-colored acrylic paints, and it dries faster. Water-based polyurethane has a lower resistance to moisture, which is why it is best to use it on indoor surfaces.
What are The Benefits of Polyurethane over Acrylic Paint?
Here are some reasons why you should consider adding a coat of polyurethane over acrylic paint on wood:
- Acrylic paints are generally dry, dark, and dull. Adding a layer of polyurethane makes the paint appear brighter and smoother with a glass-like finish. Polyurethane adds life to acrylic paint.
- Polyurethane prolongs the paint’s lifespan by protecting it from wear and tear, abrasion, fading, and chipping.
- Polyurethane forms a plastic coat over the acrylic paint shielding it from moisture, heat, chemical, and fungi damage.
- Acrylic paints penetrate wood pores but don’t protect them from water damage. Polyurethane has waterproofing qualities and protects the wood and paint against water damage.
- Polyurethane coats make acrylic paint surfaces easier to maintain. It is generally easier to clean dirt, dust, and grime off surfaces with polyurethane than a coat of acrylic paint. Applying poly over the paints makes cleaning simpler.
Can You Use Polycrylic Over Acrylic Paint?
You sure can! Polycrylic is one of the best clear coats to apply over acrylic paint. Polycrylic is similar to polyurethane, only that it is water-based and entirely non-yellowing. It forms a silky smooth solid coat over acrylic paint, protecting it against heat, water, and UV light damage.
Polycrylic is less toxic than polyurethane and also less durable. It tends to appear whitish over darker-colored paints. Polycrylic is readily available in satin, semi-gloss, and high-gloss finishes.
How Long Should Paint Dry Before Applying Polycrylic?
Acrylic paint takes approximately 20-30 minutes to dry to touch and 6-12 hours to fully cure. Only apply polycrylic on cured paint.
Dry and cured paint is solid and firm. If it feels sticky, give it more time to dry. Use your fingernail to determine if the paint is cured. Poke the paint with your fingernail; if it forms an indentation, it’s not cured yet. When no marks form, you can apply your polycrylic.
How Long To Wait Before Putting Polyurethane Over Acrylic Paint?
Always wait till the paint cures before sealing it with a coat of polyurethane.
Artist’s grade acrylics are denser than students’ grades and take longer to dry. The duration of the wait depends on the number of coats applied. Give acrylic paint approximately 72 hours before adding your layers of polyurethane over it.
Cleaning and sanding over uncured paint damages it and the wood, which ruins your entire project.
Factors Influencing The Drying and Curing Time of Polyurethane Over Acrylic Paint
Here are the reasons your coat of polyurethane may take longer to dry:
A) Temperature
Polyurethane dries by evaporation, and just as liquids evaporate faster in hot temperatures and slower under low heat, so do the solvents in polyurethane.
The recommended temperature is between 70-77 degrees Fahrenheit. If it’s too hot during the warmer seasons, work indoors and adjust your air conditioning, fan, and thermostat.
B) Humidity
Humidity and temperatures go hand in hand. The hotter it is, the less humid the air should get, and vice versa–unless it is a tropical climate.
Use a dehumidifier to keep the air-water levels between 50%-70%. If the room is extra humid, water droplets form over the polyurethane and form bubbles. The high moisture content will cause the paint to crack and peel.
C) Type of wood
Some wood species, like rosewood and aromatic cedarwood, contain chemicals that interfere with paint adhesion. Avoid painting over these types of wood; when you do, give the paint enough time to dry.
D) Type of paint and poly
Oil-based polyurethane takes longer to dry than the water-based formula. The drying time of acrylic paint depends on its type, shade, thickness, and brand. For instance:
- Milk and chalk paint dries in 30 minutes and takes 30 days to cure.
- Latex or water-based paint dries in 2-4 hours and cures in 21 days.
- Oil-based paints dry within 6-8 hours and cure in 30 days.
E) Ventilation
Air circulation plays a part in how fast polyurethane dries and cures. Proper ventilation reduces the water vapor levels in the air and boosts evaporation, leading to faster drying. You can use a fan or HVAC to boost the air circulation in your workspace.
F) Dirty surfaces
Dirt and dust particles tend to stick to the surface when sealed over. If the surface gets dusty or you don’t clean up the dust properly after sanding, the polyurethane takes longer to dry. Let the painted surface dry in a dust-free area, and use a tack cloth to wipe off the sanding dust.
G) Applying thick coats
The thicker the coats of polyurethane, the longer it takes to dry. Apply thin coats, and after it dries, add subsequent coats. 2-3 layers of polyurethane are enough to achieve a smooth glossy finish.
H) Short drying time between coats
Give each layer of polyurethane enough time to dry before adding another coat over it. The oil-based polyurethane takes longer to dry than water-based poly. If you add another coat over a previously wet polyurethane, the final coat will take much longer to dry.
Polyurethane Alternatives to Apply Over Acrylic Paint
Other than polyurethane, below are some alternatives to consider when sealing acrylic paint:
- Varnish
Varnish has been in use as a paint sealer for years. You can use two types of varnishes: resin and polymer varnish. Resin varnish is more durable, strong, and glossier. However, the resin varnish is more toxic and pungent, so you must wear protective gear.
Polymer varnishes, on the other hand, are less toxic and leave surfaces with a smooth finish. You can find the varnish in gloss, satin, and matte finish. You can apply the varnish over dry acrylic paint with a brush or spray-on.
- Furniture wax
Furniture wax is a simple yet effective way to seal acrylic paint on wood. All you need is a lint-free rag and spread the wax evenly on the painted surface. Buff the wax after a while to attain a glossy sheen.
- Epoxy resin
Epoxy resin does a remarkable job sealing acrylic paint. It makes the colors pop and dries to a beautiful glossy finish.
You mix the epoxy resin with a hardener for better results, depending on the type. You can use a resin calculator to determine the amount of resin to use.
- Glaze
Glaze is a protective medium applied over paint or stains to make them durable. Glaze is better on indoor acrylic-painted pieces as it offers no protection against heat and water damage. It is easy to apply, and it dries within 30 minutes.
- Mod podge
Mod Podge is a clear, waterproof sealer popular among crafters. Mod Podge is quick-drying, easy to apply, and comes in a glossy or matte sheen. Using a brush, apply thin coats of this product over the paint and let it dry.
- Polycrylic
Polycrylic is a water-based polyurethane alternative that leaves a clear satin of high gloss finish on the paint. It is better for interior use and doesn’t form amber tones over time. Polycrylic is available as a spray-on or roll-on sealant.
- Clear coat sealers
The clear coat is an aerosol sealer suitable for indoor or outdoor use. It quickly dries and protects the paint against wear and tear on heavy traffic surfaces. It protects against abrasion, scratches, and moisture damage.
- Acrylic medium gel
You can apply the acrylic medium gel to paint with a brush, sponge, or roller. Or you can add the product to the acrylic paint to boost its adhesion and make it more durable.
- PVA glue
Polyvinyl acetate glue is an affordable product that can seal acrylic paint. You’ll need to dilute the glue with water before applying it over the paint with a brush.
Polyurethane Over Acrylic Paint: FAQs
Here are answers to frequently asked questions about applying polyurethane over acrylic paint:
Can you apply polyurethane over high gloss paint?
Yes, polyurethane goes over high-gloss paint and makes it glossier. Polyurethane forms an impenetrable coat that helps the high gloss paint retain its sheen and protects it from water damage and harsh weather elements.
You’ll need to ensure the paint is dry and fully cured before adding your coat of polyurethane, though.
Do you need to sand in between coats of polyurethane?
Yes, the polyurethane finish appears smooth and more even when you sand. Sand the surface of your polyurethane coat lightly before adding a subsequent coat to promote adhesion and better results.
Sanding helps the layer of sealant to adhere to each other, and it is the best way to remove scratches, imperfections, and drips sustained while applying the underlying coat. Use a fine-grit paper sander and apply gentle pressure to avoid damaging the existing coat.
How many coats of polyurethane should you put over acrylic paint?
Apply at least two coats of polyurethane over the acrylic paint for maximum coverage. You can add other coats depending on your preference. Please read the manufacturer’s instructions on the number of coats they recommend and the drying time for each.
Can polycrylic go over acrylic paint?
Yes, if the paint has cured, you can apply polycrylic over it. Polycrylic is resistant to yellowing and gives the paint a smooth and glossy finish. It is best to use polycrylic on the interior rather than exterior surfaces as it is susceptible to moisture, heat, and sunlight damage.
Can you use acrylic enamel over a polyurethane primer?
Acrylic and water-based latex products are not the right choices for conditioning polyurethane. Use oil-based primers for oil-based paints and water-based primers for water-based paints or oil-based primers compatible with water-based paints.
All in all, paint won’t bond to polyurethane without a primer. You can apply acrylic latex paint on surfaces exposed to less traffic and stress, while oil-based enamel and acrylic enamel are more durable on surfaces highly prone to duress.
What can I put over acrylic paint to make it glossy?
You can achieve a glossy finish with polyurethane or polycrylic sealers. Other polyurethane alternatives explained above include varnish, mod podge, acrylic medium gel, furniture wax, clear coats, PVA glue, glaze, and epoxy resin.
Can you clear coat over acrylic paint?
Sure, you can use the aerosol clear coat sealant over acrylic paint. It is easy to apply and protects outdoor and indoor painted surfaces. Clear coats work painted surfaces like wood, canvas, metal, plastic, and ceramic.
Can you put oil-based polyurethane over acrylic paint?
Oil-based polyurethane is an excellent protective sealer for acrylic paint. It is water resistant and protects against heat, moisture, insects, UV light, and fungi damage.
Polyurethane Over Acrylic Paint: Bottom Line
It doesn’t matter whether you go over the moon picking out paint designs or color compositions or buying expensive bristle brushes; acrylic paint still fades. However, a coat of polyurethane over acrylic paint can prevent premature fading.
Polyurethane makes the existing acrylic paint appear vibrant, smooth, and shiny. It also prolongs its service life by protecting it against moisture, heat, sunlight, fungi, and insect damage.
The best way to preserve your acrylic paint job is by sealing it, and polyurethane is a good choice of sealant.
We hope this article answers the “what ifs” and other nitty-gritty concerning applying polyurethane over acrylic paint. Feel free to share your experience with us in the comments.
Happy woodworking!