How Long Does Paint Need to Dry Before Polyurethane?

Image of painted wall but How Long Does Paint Need to Dry Before Polyurethane?Polyurethane finishes are the undisputed winners in creating the perfect, durable protection for your surface. Apart from its excellent performance, it is easy to apply, cures relatively quickly, and dries rock-hard. On a painted surface, polyurethane is especially useful since it allows the beauty of the painted surface to shine through while offering it maximum protection. So, it becomes important to answer how long does paint need to dry before polyurethane.

To get the best results, allow the paint to cure completely before applying the polyurethane. When the paint dries, it means that the solvents have evaporated from the paint, leaving it dry to touch.  However, a cured paint has achieved maximum hardness. Depending on the paint you use, the cure time for your paint could be anywhere from 5 to 30 days.

One way to test if your paint has cured is to do the fingernail test, where you press your fingernail into the coating, and if it leaves an indent, it has not cured fully. The article below will focus on applying polyurethane over paint correctly and give tips on how to make the entire process easier.

How to Apply Polyurethane Over Paint

The steps listed below offer a comprehensive guide on how to apply polyurethane over paint best.

Step 1: Preparation

Applying the polyurethane on a surface that you have adequately prepared ensures that it looks the best and endures. First, you need to wash the surface. You must wash off dirt, grease stains, and any other type of filth before applying the first polyurethane coat. Apart from cleaning the surface, you will also increase the adhesion of polyurethane to the surface by de-glossing its finish.

A great detergent to use for this is trisodium phosphate, a blended cleaning product that painters use to make sure that a surface is clean. You can start by mixing a half cup of the detergent with some water and using a soft sponge or rag to wipe the surface clean. 

After cleaning the surface, the next step will be to scuff it. Sanding aims to flatten the sheen with scratches that are not large enough to show under the polyurethane. You can sand by hand using fine-grit sandpaper or use a palm sander. If you are preparing a painted floor, you can use a buffer together with the sandpaper.

Step 2: Choose the product 

When choosing a polyurethane product to use, you can either go for an oil-based or water-based finish. Below is a discussion on these two types of finishes and the situations each one is suited to.

  1. a) Oil-based polyurethane

An oil-based polyurethane finish has mineral and petroleum products as the medium for the polyurethane solids. The oil-based finish results in a hard shell on your surface using fewer coats than water-based products. The coats are also self-leveling and will become smooth when applied to a horizontal surface.

However, the coats do take a relatively long time to finish drying with every coat. Oil-based polyurethane also has a sharp, definite smell, which most people find unpleasant, though it does go away after it cures. Also, this type of finish tends to yellow as time goes by.

  • When Do I Use Oil-based Polyurethane?

Oil-based polyurethane is a great choice for countertops, cabinets, and wood floors because the coatings offer great scratch resistance. However, the high build offered by this type of finish can allow using only one coat. Because of the drying time of this finish, it will also require more time to cure fully, with more time for more coats.

You can also use it if the hardness of the finish is an important factor for you since this oil-based finish dries harder than its water-based counterpart. When using oil-based polyurethane, it is vital to work in a well-ventilated room and use protective respiratory equipment when recommended by the manufacturer.

  1. b) Water-based polyurethane

Contrary to the oil-based finish, water-based polyurethane has water for a solvent base rather than petroleum products. Water-based polyurethane can form a hard shell-like its oil-based counterpart, although it will need more coats to achieve this.

Another significant difference between these two finishes is the drying time. Water-based polyurethane dries faster, and you can apply many more coats in much less time. This finish starts off being milky white while in the can, but it dries clear after application.

Another difference is that this type of polyurethane has almost no odor. Also, while you need to use mineral spirits to clean up oil-based polyurethane, you can clean up water-based polyurethane using only warm water and soap.

When Do I Use Water-based Polyurethane?

Water-based polyurethane is a great option if you are looking for a quicker-drying product. It is also a great option if you want the paint color to remain unchanged and visible under your finish. However, it is also crucial to note that water-based polyurethane is a less durable option against scratches than the oil-based finish and is a good option for surfaces that are not as exposed and will not see much rough use.

A quick tip is that it is a good idea to cover air vents and ducks leading to the room to minimize the dust in the air.

Step 3: Choose the applying tool

You can either spray the polyurethane or use a brush to apply oil and water-based polyurethane to a painted surface. If you choose to spray the polyurethane, we recommend not thinning it out beforehand.

The product will already be thin enough to spray from the can, and thinning it out more may cause it to run. We also recommend that you not use a roller to apply the finish as it can leave bubbles that can harden into the finish.

Step 4: Apply the first coat and scuff.

You can then apply your first coat of finish to the surface and allow it to dry as per the instructions listed by the manufacturer. After the first coat has dried, use sandpaper to scuff the surface once more. Doing this will allow you to remove any dust particles and flatten any bubbles that may have hardened into the finish.

Step 5: Apply the second coat. 

The necessity of any extra coats will depend on the type of polyurethane finish you are using and your discretion. Surfaces that will see a lot of hard use and wear will require more polyurethane coats. Allow the final coat around an extra full day to ensure that it Is completely dry before handling the surface.

Tips 

  • Stir the polyurethane using a paint stick instead of shaking it to keep it free of bubbles.
  • Use a natural-bristle brush over a foam brush.
  • Run the paintbrush over the surface at a 45-degree angle to the application angle before the surface dries to smooth out any air bubbles.
  • Vacuum the dust from each sanding before applying the next coat.

Do I Have to Sand Paint Before Polyurethane?

Yes, we do recommend sanding paint before you apply polyurethane. One of the main purposes of sanding before applying the polyurethane is to get rid of any brushstrokes or drip marks on your surface before applying the subsequent coats of finish.

When sanding polyurethane, you can use 220-grit sandpaper or higher since using finer sandpaper helps to remove brushstrokes, bumps, and any unevenness to attain a smooth surface.

What Happens If You Don’t Sand Between Coats of Polyurethane?

The contrast in finish between a sanded and un-sanded polyurethane coat is not visible to the naked eye. The layers of polyurethane will still adhere together whether you sand them or not.

However, there will be differences in the texture of the polyurethane coat in sanded vs. un-sanded surfaces, with the un-sanded surface being slightly rougher and having tiny bumps. But even this difference in texture only becomes glaring when next to the surface with sanded polyurethane layers.

Therefore, if you don’t have enough time or are working on a project where the final texture must not be perfectly smooth, you can skip sanding between coats without significant impact.

How Do You Smooth the Final Coat of Polyurethane?

The final coat of polyurethane should be smooth and still have its sheen without having numerous scuff marks. Below are different methods you can use to smooth your final polyurethane coat.

  1. Dry sanding

Although this method can be effective, it is not preferred as it leaves scuff marks on the polyurethane. We recommend using fine-grit sandpaper, as anything higher will likely leave the surface looking cloudy. Put the sandpaper on a sanding block so that you can sand more evenly and accurately, and gently swipe it over your polyurethane surface.

You must work extra carefully to avoid a clouded surface. Clean the surface using a tack cloth, and if the surface still has any imperfections, you can then go in with finer grit sandpaper.

  1. Wet sanding

When working with polyurethane, wet sanding is usually the best way to ensure a smooth finish. After the polyurethane has dried completely, use a spray bottle to spray water or mineral spirits to the surface. It is important to note that you can only use the mineral spirit for oil-based poly, while you can use water for both types of finish.

You can then do the next steps by hand or using an orbital sander. For the sander, fit it with a sheet of 2000-grit sandpaper, and turn the machine on to a low power setting. Proceed to rub the sander in slow, horizontal motions across your surface.

Apply an even and light amount of pressure as you move from one side to the other. Ensure that you use sandpaper labeled as ‘wet/dry. You can also choose to use a scrubbing pad with your sander.

When wet sanding by hand, use a piece of superfine sandpaper such as 1500-grit and rub it down along your surface using smooth and even motions. If you don’t have superfine sandpaper, it is ok to use a lower grit level. You can wrap the sandpaper around a Styrofoam block so that you have an easier time working it.

Wipe away any residue you see on the surface gently using a clean cloth. Touch the surface to see if the imperfections are gone, and if not, buff again in long, slow motions. If the sandpaper you are using starts to get clogged with residue, switch it out for a fresher piece.

  1. Using polish.

Polishing, instead of sanding the surface, is a great way to get a glossy finish. To do this, replace the sandpaper pad in your orbital sander with a one-inch-thick foam insert. Then spread a good amount of car polish over the foam pad.

When using polish, it is vital to ensure that the one you are using is clear and not meant for dark exteriors. You can easily acquire car polish in an auto supply shop or purchase it online. Turn on the orbital sander and set it at a low speed. Start working the polish into your polyurethane surface with long, horizontal motions while applying a small amount of pressure. 

The surface may take a few minutes before becoming shiny as the polish gets buffed in. If there is any polish residue on the surface, use a polishing cloth to finish buffing that. Rub the surface until it becomes glossy and reflective. As the name suggests, you may need to use a swirl mark remover to remove any swirl marks. Be careful when buffing around corners to not burn through the finish.

  1. Waxing 

Waxing your final polyurethane coat is the way to go if you want a satin finish. Apply a paste wax coat to the surface by rubbing it using smooth circular motions until you can see no more scratches in the finish. For an easier and more even job, use short strokes and start by applying wax to the end sections while following the grain.

Use a paper towel to remove any residue from the surface before the wax has a chance to dry. Allowing wax to dry in your polyurethane will make your surface feel uneven. Still, if any wax dries on the surface, sprinkle some water on the surface, use a clean 0000 steel wool pad to brush down the surface lightly, and blot away the water using a clean cloth or paper towel.

What Paint Will Stick to Polyurethane?

Oil-based paints are the best option when painting over a polyurethane surface. They adhere to the primer best and are usually longer-lasting than water-based paints. However, apart from the type of paint, other factors such as painting over the polyurethane without prepping will cause your paint to peel off. So, how do you properly paint over polyurethane?

Step 1: Prepare the surface.

Before you do anything, put on the proper protective equipment and work in a well-ventilated area if you cannot work outdoors. Then clean the surface. Trisodium phosphate is a strong cleaning agent for this, though if you want a milder solution, you can use some water and dish soap. Scrub the polyurethane surface firmly using a sponge until the surface is clean, then wait for the surface to dry completely.

If there are holes, cracks, or chips on the surface, you can fill these up using wood putty and allow them to dry.

Step 2: Sand the surface

Scrub the polyurethane surface with fine-grit sandpaper using circular motions. Doing this will scuff up the polyurethane surface so that the primer and paint adhere to it. After sanding, you can vacuum up all the dust from the surface and wipe it down with a clean, damp rag.

Step 3: Priming and painting

Using a paint roller for larger surfaces and a paintbrush for smaller, harder-to-reach surfaces, you can do this step. Apply a thin coat of white, oil-based primer to the surface and allow it to dry completely, then follow that up with a coat of oil-based paint. Apply as many coats as you need to get your preferred coverage, allowing the paint to dry completely between coats.

Tip

If you are not stripping your surface, using enamel paint will give you the best results.

How Many Coats of Polyurethane Should I Put On?

The number of polyurethane coats you will need depends on several factors, such as the type of poly you are using and what surface you will be applying it to.  When using oil-based polyurethane, a minimum of two coats should be enough to offer protection. However, floors and other surfaces that are likely to see hard use should get a minimum of three coats. 

For water-based polyurethane, start with a minimum of three coats for protection, with at least four coats for surfaces that need extra protection. Oil-based poly will need fewer coats since it has a higher build.

When applying the coats, remember to let the coats dry before application of a subsequent layer.

How Many Coats of Polyurethane Is Too Many?

After a certain point, additional layers of polyurethane are not of any benefit. Again, the number of coats will depend on the area’s traffic and the type of polyurethane. For oil-based polyurethane, adding more than three coats for an area without much traffic will not do much good, while for a water-based poly, four coats are enough.

How Long Should You Let Polyurethane Dry Between Coats?

The drying time of the polyurethane finish is affected by several factors, such as the type of polyurethane you are using (water or oil-based), the thickness of the coats you apply, and the environmental conditions. 

Oil-based polyurethane takes longer to dry than water-based polyurethane and will dry and cure completely in about 24 hours. This drying time means that you can only apply one coat of this finish per day. On the other hand, water-based polyurethane takes a much shorter time to dry-around 4 to 6 hours. Therefore, you can apply several coats of water-based polyurethane on the same day.

You can tell that the oil-based poly is dry if it is no longer tacky to the touch and emits an odor. For water-based polyurethane, you can tell it is dry if it is no longer col to the touch, and a light powder forms with sanding. 

  • How to Make Polyurethane Dry Faster

Sometimes, you may not have the hours to a day needed for each coat of polyurethane to dry fully. You can use several tips and tricks to ensure that the polyurethane dries faster, as listed below.

  • Buy a quick-drying polyurethane. A quick-drying polyurethane will significantly cut the drying time. You could also opt to use water-based poly, which dries faster if time is short.
  • Use a high-build polyurethane. The high build will reduce the number of coats you will need hence faster application time from start to finish.
  • Ventilate the room. Open the windows and doors to improve air circulation. Better ventilation will increase the rate of evaporation which will result in faster drying.
  • Use a space heater. The best temperature for polyurethane drying is around room temperature. Use a space heater in the adjoining room to keep the temperature at around this range.

Tips

  • Do not try increasing the drying time by raising the temperature above normal room temperature.
  • Adding naphtha or any other thinner to polyurethane will not increase the drying rate.

What Do You Do After the Final Coat of Polyurethane?

As mentioned above, there are several methods you can use to smooth out the final coat of polyurethane. You can choose to dry sand the surface, which might leave scuff marks if you are not careful, wet sand the surface, which is a better option, polish the polyurethane surface till it is glossy, or apply wax to give it a satin finish.

How Do You Fix Bad Polyurethane?

Although polyurethane has several advantages over other finishes, it still has some cons, such as the tendency to form bubbles that can harden into the surface with time. Other problems that may arise include cracks, separation, and blushing, and runs. However, you can solve most of these problems relatively easily.

Below are some tips on how to troubleshoot problems with polyurethane.

  • Bubbles that appear when you are painting polyurethane are because of the paintbrush’s turbulence or moisture released by the substrate. You can keep them from forming by brushing slowly and applying the polyurethane at moderate temperatures.
  • If the bubbles have hardened into the finish, use 200-grit sandpaper for sanding them down, then recoat the surface after taking measures to keep them from reforming.
  • If the finish is cracked or checked, sand it with fine-grit sandpaper and recoat the surface. Checks and cracks are likely to appear when a thick coat dries too quickly, such as on a hot day.
  • Scrape off dried drips using a razor or sand using 20-grit sandpaper and recoat.
  • If the finish turns cloudy after drying (blushing), remove the finish with an oscillating tool and sandpaper. Clouding can happen because of moisture in the wood. After you remove the finish, allow the wood to dry before you recoat it.

Can You Put Oil-based Paint Over Polyurethane?

Yes, you can. Oil-based paint is excellent for painting over polyurethane-treated wood. Oil-based paint will adhere to the primer better and be more durable than water-based paint.

How Do You Paint Polyurethane Foam?

Flexible polyurethane foams are usually used mainly for assembling doors and windows, insulation, waterproof barriers, and infilling. Though it has several uses, it presents a great challenge to paint. Below is how to best paint foam on a surface.

Step 1: Prepare the foam.

Before you prepare the foam, first prepare the working area. Find a well-ventilated area and put on personal protective equipment. Cover the working area with newspapers to avoid making a mess of the working area.

In a bowl, mix a paste of wood glue and water with a 1:1 ratio and mix with a stick until it is thick and not too liquid. The consistency should be jelly-like.

Apply the paste to the foam until you cover the surface of the foam. Depending on the temperatures, your paste could take up to 24 hours to dry. Ensure that the paste is completely clear before you begin painting.

Step 2: Paint the foam.

It is important to prime the surface of the foam before painting to provide an even surface. If you are painting a wide, flat surface, you can use a flat brush and an angular flat brush for filling corners.

Is Two Coats of Polyurethane Enough On Hardwood Floors?

As mentioned above, the number of coats of polyurethane needed for hardwood floors varies depending on the type of polyurethane you are using and the expected traffic and use of the surface. With water-based polyurethane, two coats will provide the minimum protection for areas that do not see much use. For oil-based polyurethane, which has a higher build, two coats might be enough.

Final Thoughts

Applying polyurethane to your painted surface is one of the best ways to preserve the surface, increase its aesthetic value, and allow the beauty of the paint to shine through. When done correctly, the results can be breathtaking. Still, the question remains, 

How Long Does Paint Need to Dry Before Polyurethane

For the best results, paint needs to cure before you apply polyurethane. Latex and water-based paints will cure after about 21-30 days, while oil-based paints cure after about seven days. 

Thank you for taking your time to read our article, and we hope you’ve learned something. You can leave any comments, questions, and suggestions in the comment section below.