Can You Use Interior Paint Outside (Try These Techniques!)

Most often than not, we don’t end up using all the paint in the bucket while repainting a room or a corridor. And considering how pricey quality paint is, it’s not a wise idea to throw away any of it. So, can you use interior paint outside?

Yes, you can use interior paint outside. However, it’s highly recommended not to use it outside to avoid untimely fading, flaking, and cracking. Interior paint isn’t as pigmented as exterior paint, nor does it contain as many binding agents. Hence, interior paint isn’t as long-lasting as exterior paint since it can’t easily withstand the weather extremities.

While it’s best not to use interior paint outside, you don’t necessarily have to throw away the leftover paint either. Today, let’s go over a few ways we can make the best out of the situation without having to compromise on the quality or the longevity of interior paint. Additionally, we’ll also check out what sets interior paint apart from exterior ones.

Why Is Interior Paint Different From Exterior Paint?

The paint components are more or less the same in both cases. Just the ratio varies in order to fulfill certain criteria.

Here’s a brief overview of the prime differential components in both interior and exterior paint-

Flexible Vs. Sturdy Binding Agents

With interior paint, the resin quality is sturdier than usual. The resin is meant to withstand day-to-day scuff marks and accidental scratches. Consequently, it’s supposed to give the walls a glossier finish in the case of latex and acrylic paint.

In addition to the scratch-prevention benefits, the stable resin component helps keep the walls clean. You can simply wipe the dirt and stain off the walls with some soap and lukewarm water. Most of the time, even a simple swipe with a soft muslin cloth is enough to wipe everything off.

This type of resin isn’t used in the exterior paint bases simply because the quality will deteriorate in the scorching heat. While the resin is great for indoor rooms and corridors, it’ll crack just as easily when it’s constantly exposed to the sun.

Hence, a more flexible formula is used for the resin in exterior paint. Even if the paint expands in the presence of extreme heat, it won’t crack when it contracts later on.

Mildew Prevention

Like temperature, exterior paint needs to withstand extremely foggy weather as well. Hence, the paint comes with innate fungicidal components to battle mildew and other pests.

The additives in the exterior paint contain a high amount of VOCs (Volatile Organic Compounds) for this purpose. Needless to say, it’s harmful to human beings to inhale these compounds, and as such, interior paint doesn’t contain a high amount of VOCs.

Hence, if interior paint is used outside, the surface will be damaged easily as the paint won’t be able to fight the mildew. Within a couple of months, you’ll notice the growth of moss, fungi, etc., which will weaken the structure even more. 

How Can You Use Interior Paint Outside?

It’s not a wise idea to replace exterior paint with interior ones. However, here are a few ways how you can use the leftover interior paint on outdoor projects –

Mix The Two Kinds Of Paint

It’s best not to use interior paint outside without changing the composition of the paint first. So, if you’ve got some leftover paint, use it by mixing it with some exterior paint instead.

Make sure the ratio tilts in the direction of the exterior paint. Because the durability of the mixed paint is directly proportional to the ratio of the two types of paint.

If you dilute the mixture with too much interior paint, the durability of the exterior paint will take a major hit. Hence, to prevent that, keep the ratio one-sided. For instance, if you use 1 ounce of interior paint, use 9 ounces of exterior paint to ensure maximum durability of the mixed paint.

Recoat With Exterior Paint

If you don’t want to go through the hassles of mixing the two kinds of paint, you can recoat with exterior paint instead. First, apply a proper layer with the interior paint.

Normally, interior latex or acrylic paint takes about 2-3 hours to dry before you can apply another coating. But give it 4-6 hours in this special case so that the paint can have the time to stick to the surface. After 4-6 hours, reapply the paint for the second coating, but this time, use exterior paint instead.

Make sure the first layer is completely dry. Otherwise, the second layer won’t sit on top of it at all. And you’ll have to fix the lumpy and grainy surfaces all over again. You can apply a third layer after another 3-4 hours, and this time, cover the edges perfectly.

Use Exterior Sealants

After applying multiple coatings with interior paint, you can simply use a premium-quality sealant to protect the paint. While it’s not an ideal solution, it’s certainly a nice fix.

The additives in the exterior paint already contain these sealing agents to avoid deteriorating conditions. So, by using these clear-coat polyurethane sealants, you can protect the texture of the paint & the overall quality of the finish as well.

Strategic Placement

Interior paint isn’t all that different from exterior paint, apart from the fact that it can’t withstand the outside extremities. Hence, while renovating, find out all the nooks and crannies where the weather conditions don’t matter as much.

For instance – the walls and areas under the extended roof, the outside walls of a barn, the checking booth, etc.

Make a list of all these places and use the leftover interior paint to paint these places during a renovation project.

If you use interior paint somewhere with a lot of shade, the surface coatings will crack less. And in turn, the paint will last a lot longer than usual.

Using Interior Paint Outside: Safety Protocols

While interior paint won’t last in the outside weather for too long, you can extend the longevity with a few tricks.

Check out the following safety protocols to ensure a quality finish even if you’re using adulterated interior paint outdoors –

Go For A Test Run

The binder quality is one of the premium differential components between interior and exterior paint. Interior paint uses a stronger binder so that it not only sticks to the wall but it’s also sturdy enough to resist abrasion.

The problem with this is – if you’re using the same paint outside, it won’t want to stick to the walls as easily.

And why not?

Because the sturdy binders aren’t built to withstand the extremely humid weather or the heat of the scorching sun. So, when you take those environmental conditions into account, the binders will either expand or contract. Either way, they’ll end up cracking, and you’ll have a flaky surface.

So, the best way to make sure that doesn’t happen is to go for a test run first. Don’t paint all of the walls at once. Paint one and keep it under surveillance for a couple of weeks. If you notice any expansion in the coating, don’t use the same paint on the other walls unless you change the formula or the ratio.

Wear Face Masks

Exterior paint contains a huge amount of volatile organic compounds. So, while mixing the two kinds of paint, make sure to wear face masks before opening the cans. Because inhaling the paint fumes can lead to life-threatening illnesses. Read up on – How Long Do Paint Fumes Stay In Your System?

And not just during the mixing. You should wear face masks while painting as well. No matter how amazing the smell might feel, don’t inhale the fumes directly.

Use Premium-Quality Sealants

If you’re using clear-coat polyurethane sealants, make sure to follow two important precautions. One – only purchase top-notch sealants to avoid premature cracking & yellowing. And two – use at least two coats to protect the inner paint.

Unfortunately, due to the weather extremities, the clear sealants will eventually turn yellowish beyond comprehension. That’s why, even if it’s a quick fix, it’s not necessarily a good fix. Plus, polyurethane sealants are really costly as well.

Frequently Asked Questions

Q: Does interior paint take longer than exterior paint to dry?

The drying period mostly depends on the paint type and environmental conditions. Typically, it takes latex interior paint around 1-2 hours to dry up just enough for the 2nd coat. Again, exterior latex paint will take around an hour or so to dry unless the weather is really humid.

However, with oil-based paint, you’ll need to wait for at least 6-8 hours before you can reapply the paint. Again, if there’s a thicker spread, it can take much longer than that. And for the paint to dry completely, it’s best to wait for 2-3 days.

Q: Should I repaint the exterior walls if I accidentally use interior paint outside?

You don’t have to repaint the walls right away. Since interior paint isn’t well-equipped to handle the outside weather, the surface paint will likely peel off in a few years. Other than the short-lived texture, the interior paint won’t cause any structural harm to any of the walls.

Q: How long can interior paint survive the external weather?

If you use unadulterated interior paint outside, the surface coating will start to become brittle within 2-3 years. Alternatively, quality exterior paint will last for at least 12-15 years without showing signs of degradation.

Again, a proper mixture of interior and exterior paint can survive the heavy weather for 5-7 years, if not more.

Q: Will I still be eligible for a warranty after mixing interior paint with the exterior ones?

No, the warranty is no longer applicable if you mix the two. No store will take those cans back after you’ve compromised the composition of the paint itself. However, if you mix the two in a separate container, then it’d be a much different case. Keep the original cans intact if you’re planning on using the warranty services, irrespective of the brand and kind.

Before You Go

While it’s best to stick to indoor projects whenever you’re using interior paint, you can use the paint outside as well. However, make sure to follow the proper mixing guidelines. Otherwise, you’ll have to work with lumpy paint instead.

And if you’re interested in knowing more about quick paint fixes, go check out – Can You Spray Paint Styrofoam?

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