Can You Apply Polyurethane Over Latex Paint? (How-To)

Polyurethane is a common sealant used to seal and protect various paint types. But can you put polyurethane over latex paint? Here is the answer to that.

Polyurethane can be used on latex and other water-based paints. This is because sealants like polyurethane adhere to water-based paint coatings. Polyurethane either water-based or oil-based will stick properly to latex paints.

The polyurethane finish will also protect the latex paint and give it a glossy sheen making it reflective. But that’s not all. There is more to know about using polyurethane on latex and this post digs right in.

Also, keep your eyes peeled for helpful tips in this post. So, let’s get to it.

How Long Should Latex Paint Dry Before Applying Polyurethane?

The latex paint has to cure before polyurethane can be applied over it. It takes between one hour and 24 hours for latex paint to dry enough for polyurethane application.

On average, you can apply polyurethane over latex paint 6 hours after the final coat of latex paint was applied.

When it comes to applying polyurethane over latex paint, you need to wait till the final coat of latex paint has cured. This means when the solvent (water) has been fully evaporated from the paint particles. On average, this takes about 6 hours.

When the solvent is completely evaporated, it completes the curing process of the latex paint making the paint coating harden. When the paint coating has hardened, then the polyurethane when applied will stick well to the latex paint.

If you apply polyurethane over latex paint that hasn’t cured, the polyurethane will not sit well on the latex. This is because there will still be moisture trapped inside the latex paint coating. This will cause the latex paint to become tacky or wet.

The tackiness is a result of improper water evaporation in the latex paint. Eventually, the polyurethane finish will turn cloudy or whitish. The finish can also start to peel off after a while especially if it’s oil-based polyurethane.

The best polyurethane to use on latex paints is water-based polyurethane. Oil-based polyurethane will also work fine on latex paint. But, after a while, the oil-based polyurethane will begin to develop a yellowish tint.

The yellowish tint is caused by the large volume of oils, paint chemicals, and VOCs (volatile organic compounds) in the oil-based polyurethane.

Water-based polyurethane on the other hand will remain clear for years.

However, oil-based polyurethane is stronger than water-based.

Does Polyurethane Seal Latex Paint?

Polyurethane seals latex paint nicely. The polyurethane when applied seals the latex paint coating by forming a clear ultra-thick film. That film makes the latex paint moisture-resistant.

As a sealant, the polyurethane prevents moisture from penetrating the latex paint. Latex paint is water-soluble so if exposed to high moisture levels, the latex paint will dampen and begin to peel off.

Polyurethane protects latex paint from the factors like dents, sunlight (UV rays), and scratches in the environment. These factors will ruin the latex paint and cause early chipping and paint damage.

Polyurethane like wax, lacquer, and other oil-based topcoats give additional protection to latex paint. Both the water-based and oil-based versions of polyurethane will seal latex paint.

One major reason for this is the water-based nature of latex paints. As a water-based paint type, latex paint dries quickly.

Not just that, the topcoat of latex paints when dry doesn’t form any glossy sheen or wax that prevents inter-coat adhesion. The finish of latex paint is usually textured and dry. This makes it easy for the polyurethane to stick to and seal the latex paint.

Now, let’s check out how to apply polyurethane over latex paint.

How To Apply Polyurethane Over Latex Paint (Made Easy)

Applying polyurethane over latex paint is a pretty easy task and one you can do by yourself.

To put polyurethane on latex, you’ll need the following tools:

  • Rags or Tack Cloth
  • Fine-Grit Sandpaper
  • Polishing Compound
  • Polyurethane
  • Bristled Paint Brush
  • Razor Blade
  • Paint Bucket (Optional)
  • Hair Dryer (Optional)

Here is a quick rundown of how to apply polyurethane over latex paint:

  1. Clean & Sand The Latex Paint
  2. Apply The First Two Coats of Polyurethane
  3. Apply The Final Coat
  4. Apply Polishing Compound

Now, let’s get to work.

1. Clean & Sand The Latex Paint

Clean & Sand The Latex Paint

The first step is to wipe the latex paint. This step is to remove any debris or grime on the latex coating. Use a tack cloth or rag to wipe the latex paint coating repeatedly.

Next, light sand or scuff the latex paint coating. The purpose of scuffing the latex paint is to create a smooth surface for polyurethane application. If the latex paint is affected by paint pimples, debris, or dust nibs, the polyurethane will not adhere well. So, sand first to remove imperfections.

As you sand, you also create tiny holes and scratch marks that the polyurethane can bite and adhere to. For the polyurethane to stick, the latex paint surface has to be a bit textured.

2. Apply The First Two Coats of Polyurethane

Apply The First Two Coats of Polyurethane

The next step is to add the first and second coats of polyurethane over the latex.

Usually, you need just 3 coats of polyurethane to seal and protect latex paint. More than 3 coats will turn the finish to become tinted.

Oil-based polyurethane will develop a yellowish ting if more than 3 coats are applied. Water-based polyurethane will turn whitish or cloudy.

Tip: To apply the polyurethane over latex, use a synthetic bristled paintbrush for water-based polyurethane. Use a natural bristled paintbrush for oil-based polyurethane. Here is why –

Natural bristled paintbrushes have split ends tightly packed. This makes them ideal for painting oil-based stains like polyurethane. Synthetic bristled paintbrushes have split ends a bit more apart than natural bristled paintbrushes. This makes the paintbrush able to hold up more paint thus fitting the water-based nature of latex paints.

Apply the first coat of polyurethane on the latex paint. Then wait for it to dry. On average, it takes oil-based polyurethane 12 hours to dry enough for a recoat. Water-based polyurethane dries enough for recoat in about 5 hours.

Tip: Apply polyurethane in thin coats.

When the first coating dries, sand lightly with very fine sandpaper, usually, 320 grit. Then apply the second coat. The purpose of sanding is to remove grain and dust that settled on the first coating so the second coating can stick properly.

After applying the second coat, wait till it cures. Then sand again with fine-grit sandpaper.

3. Apply The Final Polyurethane Coat

Apply The Final Polyurethane Coat

As explained earlier, you need 3 coats of polyurethane to seal latex paint. After sanding the second coat, apply the final coat.

For the final coat, ensure to apply as fine as possible. Remember, you only need thin coats of polyurethane.

Tip: While applying the final coat, don’t go back and forth with the paintbrush. It’s best to apply the final coating in one stroke. This limits brush strokes on the coating.

You don’t need to sand the final coat of polyurethane.

4. Apply Polishing Compound (Wax)

Apply Polishing Compound

You should wait at least 72 hours before applying the polishing compound for oil-based polyurethane. You should wait 36 hours for water-based polyurethane.

This time is to allow the final coat of polyurethane coating to cure before it is polished.

When the final coat has cured, apply your choice of polishing compound on the polyurethane as instructed.

Popular choices of the polishing compound include wax and linseed oil. Linseed oil and Polyurethane are used to create a finish called “French Polish”.

When you have completed all these steps, you have successfully put polyurethane over latex paint.

Can You Mix Water-Based Polyurethane With Latex Paint?

You can mix water-based polyurethane with latex paint since both paint types have the same solvent or base (water). Latex paint mixed with water-based polyurethane will dry to form a thick and strong finish.

Latex paint is also commonly used to tint Polyurethane.

Mixing water-based polyurethane with latex paint is a common practice as most painters and DIYers use this to tint Polyurethane. Polyurethane as you know is a clear topcoat.

But some homeowners don’t want clear. They want the same features of Polyurethane but with color. So painters add few drops of latex paint inside Polyurethane. Then stir and use the mixture to achieve a tinted Polyurethane finish.

But mixing too much latex paint in polyurethane will thin the polyurethane. This is because water-based polyurethane is thicker than latex paint. The thickness of the paint is one of the reasons it is so durable.

So, if you mix large quantities of latex paint in polyurethane. The thinner or lighter nature of the latex paint will thin the polyurethane – make the polyurethane paint light.

If you apply polyurethane that has been thinned, the finish will remain tacky and it wouldn’t be very durable.

Can You Put Polyurethane Over Exterior Latex Paint?

You can put polyurethane over exterior latex paint. However, you should use only exterior polyurethane on exterior latex paint. This is because exterior polyurethane is designed to withstand UV rays from the sun and other harsh exterior factors. Interior Polyurethane is not.

Generally, the paint used on the building exterior is designed with extra additives that make the paint coating resistant to UV rays from the sun. The extra additives also make the paint more resistant to wind, moisture, dust, and friction.

All of this extra work is because the exterior environment is usually harsh for paint coatings. So the exterior latex paint is designed to be stronger than interior latex paint.

This also means that the polyurethane to be used on the latex exterior has to be exterior polyurethane.

If you use interior polyurethane on exterior latex paint, the resulting finish though smooth will not last very long.. Especially, during the hot summer months.

This is because the harsher exterior environment will degrade the interior polyurethane.

Exterior polyurethane on the other hand will be strong enough to withstand whatever the exterior environment has to throw at it. Rainfall, heat, dust… The exterior polyurethane will still maintain its condition.

Exterior polyurethane on exterior latex paint will produce a very strong and durable finish.

Another thing to know is if you can use latex paint over polyurethane. Can you? Let’s find out.

Can You Use Latex Paint Over Polyurethane?

You shouldn’t use latex paint over polyurethane. Polyurethane brings a lot of benefits when used over latex paint. The reverse is the case if latex is used over polyurethane – If this is done, the latex paint will not adhere well and the whole finish will begin to peel after a while.

This is because Polyurethane when dry forms an ultra-thick and glossy film that prevents latex paint from adhering.

To put latex over polyurethane, the glossy top coat of the polyurethane finish has to be stripped off first. You can do this by using a paint stripper, alcohol-based solvent, or a heat gun.

Final words

Overall, applying polyurethane over latex paint is possible and hosts a lot of benefits if done correctly. However, you shouldn’t apply latex paint over polyurethane.

If you must, the glossy sheen of the polyurethane finish must be stripped off first.

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