Paints differ in their properties and are designed for different purposes. You’ll need to learn a little about the makeup of paint to understand the differences between exterior and interior paints.
Paint comprises pigments, solvents, additives, and resins. Water a solvent in latex paint, while mineral spirits are used in oil-based paint.
The solvent makes the paint wet until they dry after application. The resins, pigments, and additives, which are the long-term ingredients, are left. The pigment is the color that the resin bonds to the surface. Epoxy, acrylic, and even silicone can make resins.
The variance is between the two paints you see in the store. What is the difference between interior vs exterior paint? You may even have some leftover paint and wonder if you can use interior paint outside rather than purchase a new can?
In our guide, you can learn all you need to know about interior and exterior paints, the type of paint you need to use in each area, and why. (Read Enamel vs Acrylic Paint)
By the end, you’ll be well aware of the differences between interior and exterior paints.
Can You Use Interior Paint On the Exterior?
You can use interior paint on the outside of your home, yet it isn’t wise to do so. There are many reasons you shouldn’t, yet one of the most obvious being you’ll be painting again before you know it.
Here you can learn a bit more about the differences and why you shouldn’t use interior paint outside.
Water-based acrylic and latex paint can remain good for 10 years if they haven’t been opened and are never subjected to freezing temperatures.
If you have leftover paint, and hence the question, can you use interior paint outside, or vice versa. If such leftover paints are closed tightly and stored in a cool, dry place, you can use them for two years.
Interior classified paints should be used for interior use only. Right off the bat, they lack mildewcide and chemicals exterior paints contain to help them fight the effects of rain, snow, and fluctuating temperatures.
Interior paint would break down quickly when used in an exterior environment through fading, chalking, and cracking.
Interior or exterior paints have unique properties and formulated for different purposes. Interior paint is formulated to it can withstand scrubbing when cleaning and will resist staining. Exterior paints are made to combat fading and mildew.
It is good to understand the makeup of paints, so you know why to only use the right one in the right area.
Paint comes in two categories: water-based paints, better known as latex paint, or oil-based acrylic paint. (Learn How to Get Chalk Paint Out of Clothes)
Over a decade ago, they oil-based paint on exterior surfaces since it was more affordable while offering durability. It has since been shown to harm the environment and persons in the area it is applied.
Water-based paint you will find is the more common choice for interior and exterior paint projects. Luckily, there have been many improvements in the ingredients, so the performance is improved.
One advantage of water-based is the drying time is much shorter than oil-based paint. Once applied, any oil paints can take up to 48 hours to dry, and the room is unusable.
Latex paints offer minimal odor and release lower levels of VOCs (Volatile organic compounds) during the drying process.
Water-based painted surfaces are easier to clean, resist yellowing, and fading overtime when protected from sunlight. There is also less chance of them causing issues from fire as they are not flammable.
Interior and exterior paints contain four similar components:
Each playing a unique role in the product. Understanding what each does will help determine the kind of paint you need for any surface.
Pigments: Fine ground particles to make up the paint’s color. Here, you have two kinds as prime and extender. Colorants are prime pigments to deliver the paint’s color. Organic colorants will deliver bright colors, whereas inorganic colorants are earthy colors that are also durable for exterior applications.
Solvents: Liquids that suspend ingredients and thus allow you to spread paint on surfaces. In water-based paints, you have mainly water. Oil-based paints use thinners made from various solvents such as acetone, mineral spirits, turpentine, naphtha, and others.
Additives: Used to create unique properties. You can find all manner of things such as thickening, leveling, surfactants, biocides, and emulsifiers can be changed. All these can help change the properties of the application, adhesion, and stopping mildew growth.
Resins: You find these bind pigments together and thus the film of paint color. Oil-based resins are often made from linseed oil. Resins directly relate to the performance of the paint.
Is There Really a Difference Between Interior and Exterior paint?
The major difference between indoor and outdoor paint is the resins and additives. You’ll discover the binding resins used on interior paints are rigid.
The resins here allow interior paint to be cleaned easily since they offer stain-resistance. Vinyl acrylic resins can often be used when making interior paints to enhance the resistance against scrubbing and its washability.
On exterior paints, the resins used will be of a softer nature, providing characteristics to help combat fading, mildew, variations in temperature, and moisture.
Exterior paint also needs to be tough to resist peeling and avoid chips, so, to achieve this, 100% acrylic resins will be used in the composition.
Along with the above, they offer great adhesion and alkali resistance, where the paint won’t burn when applied to new concrete or masonry.
Both paints contain additives that regulate their drying time and keep the pigment dispersed in the paint mixture. You’ll see the lack of specific environmental additives in interior paint gives it a disadvantage when used on exterior surfaces.
Interior paint wouldn’t last long if you used it to paint the outside of your house on exterior surfaces through the lack of heavy-duty additives.
Exterior paints are formulated to be tougher and withstand extreme weather conditions compared to indoor paint. The tougher chemicals are designed to escape into the atmosphere.
What Happens If You Use Interior Paint Outside?
When you want to know what happens when using interior paint outside, it’s good to know that you can use either water-based or oil-based paints outdoors. However, oil-based paints are typically never used indoors since the odor and fumes can be hazardous, and there can be a lot of clean-up.
Organic pigments are found in interior paints, though certain organic pigments are susceptible to fading from prolonged exposure to sunlight and high heat.
Because of this, you’ll find exterior paints usually come formulated using synthetic pigments for longer color retention.
Acrylic or alkyd binders are most often found in residential paints and can be formulated to react differently. Most interior paints offer higher levels of abrasive resistance, thus making them easier to clean.
Resins in exterior paint are formulated to resist cracking and binding pigments for longer color retention. While having lower levels of VOCs, interior paint doesn’t have the compounds included for fighting against certain elements.
Is Exterior Paint More Durable than Interior Paint?
All paint is comprised of the same basic ingredients: solvent, resin, additives, and pigments.
When you have different paints, you’ll have solvents such as water for latex paint and mineral spirits for oil paint.
With both paints, solvents evaporate as paint dries, and leaving resin, pigment, and additives. You can find interior paints and exterior paints in different finishes, from gloss to matte.
The two types of paint have similar solvents and pigments; however, some pigments fade faster than others and are thus used for interior formulations.
Exterior paint can also contain more pigment; however, the additives and the resin make the actual difference. It is here you find the durability of one paint over the other. However, each is more durable than its counterpart in certain areas.
Exterior paints have to stand up to harsh weather conditions, from fluctuating temperatures, UV rays, and salty sea breezes in some locations.
To compensate for all this, paint on exterior walls will contain flexible resins to keep the paint looking good as the underlying surface expands and contracts. Exterior paint has additives to help prevent fading, mildew, and resist stains.
While interior paint doesn’t face the rain or sit in freezing temperatures, it is made with more rigid resins. Such resins make interior paint durable against scuffing and bangs.
Because exterior paint needs to stand up to physical abuse from the weather, it will be a better option for indoor use. (Learn How to Get Rid of Lead Paint)
That’s not actually true. Exterior paint can be more prone to scuffing and scratches. Also, it will release more VOCs (volatile organic compounds) as it dries and hardens. Even when cured, it still isn’t the best option for indoor use.
Exterior paints can contain mildewcides and fungicides, which can also expel an odor indoors. Besides, it could be possible for such compounds to trigger allergies!
When painting at home, it is far better and safer to use the project’s right paint. Professional painters use certain paints on a certain job, so why differ from their experience when you want the best finish?