Painting is a demanding job. You have to find the correct color of paint, clean up the area, and usually put several coats on before you’re satisfied. However, to get it right, you have to pick the right kind of paint as well. Interior paint was labeled that way for a reason.
You can use interior paint outside, but it’s not recommended. Interior paint has different additives and resins, which help it stick to interior walls. Interior paint was not meant for typical exterior weather conditions and will, therefore, wear out several years before exterior paint does.
In this article, I’m going to discuss the differences between interior and exterior paints and why you shouldn’t use interior paint on the exterior of your house or vice versa. I’ll also discuss what to do if you accidentally use the wrong paint.
What Is Interior Paint?
Interior paint is either water or oil-based and has various pigments added to create the proper color. Most interior paints are water-based, as this has a faster drying time and is better for the environment. It then has various binders and additives to make it stay on the wall and remain smooth.
Paint, in general, is made up of four components: a liquid base, pigments, binders, and additives. The strengths of these ingredients vary between interior and exterior paints.
Different Types of Interior Paint
There are several different types of interior paint. These paints vary in their finish and final appearance in the home. The common types of indoor paint are:
- Flat finish
- Matte finish
- Eggshell finish
- Semi-gloss finish
- High gloss finish
- Satin finish
What Is Exterior Paint?
Exterior paint has the same base as interior paint: either water or oil. Additionally, exterior paint has more pigment to withstand fading, stronger additives, and a stiffer binding agent, or resin.
These are the main differences between interior and exterior paints.
What is Difference Between Interior and Exterior Paint?
There are some critical differences between interior and exterior paint ingredients, mainly in the resin and the pigment. These differences make interior paint fall apart when it’s outside and exterior paint dangerous inside the house.
Solvents
Solvents are the base in both of them, making the paint stay liquid. Generally, this is either water or paint thinner made from oils and chemicals. Whichever it happens to be, the solvents are the main ingredients and give paint the properties that make it paint.
Binders (Resins)
The binding solution in paint is a resin made from oil. Resins make the most significant difference in exterior or interior performance in binding the color together. They determine how much harsh weather the paint can take.
Exterior paint has more resins, but they are looser. When the weather becomes extremely cold or hot, the resins expand and contract to keep their form. This prevents the paint from peeling off when it rains or snows or fading in the sunshine.
Interior paint, on the other hand, has thicker, stiffer resins. These binding agents will not stand up to more intense weather conditions but will become too brittle and break, causing the paint to chip and crack.
However, more rigid resins are perfect for interior rooms; they hold up better against scuffs, scratches, and regular cleaning without losing their structural integrity.
Pigment
Pigments are the coloring agent in paint. They are made from a variety of ingredients, both organic and inorganic. In outdoor paint, there are stronger pigments to increase the durability of the paint. Indoor colors have fewer pigments because they won’t be in direct sunlight.
Additives
The additives in the paint make it into more specific types of paints. Additives differ between the types of paint, both interior and exterior. Interior paints have additives for a smoother application to drywall. Exterior paints have additives to resist mildew and weather.
Common paint additives include:
- Fillers
- Enamel for a smooth finish
- Glitter for reflective qualities
- Leveling agents
- Bonding additives to increase durability
- Conditioners
- Thickening agents
- Scents to cover the fumes
Can You Use Interior Paint Outside?
You can technically use interior paint on the outside of your house, but it’s not advisable because it has a different chemical composition compared to exterior paint and won’t last as long on the outside walls of your home. Using it outside will result in a paint that will wear more quickly.
Manufacturers made interior paint to withstand daily wear and tear and cleanings but in a controlled climate. It’s not strong enough to take on the heat of summer sun, a winter storm, or any of the weather extremes in between. This is because the resin in interior paint is thinner than the resin on exterior paint.
Interior paint is healthier to breathe than exterior paint and made to reflect light. This finish is helpful when it’s painted on an inside wall and doesn’t get direct natural sunlight. The light-reflecting qualities help brighten up a room on the inside of the house. Interior paint is also formulated to stick to drywall and struggles to stay on any rougher surfaces.
If you paint the exterior of your house with interior paint, you might think you’re saving money. After all, interior paint is much less expensive than exterior paint. However, you won’t need to touch up exterior paint for another ten to fifteen years, whereas interior paint will need to be recoated entirely in just two or three years.
What Happens If I Use Interior Paint Outside By Mistake?
Mistakes do happen, and it’s possible to accidentally buy (and use) the wrong kind of paint. If you do that, it’s okay.
If you use interior paint outside by mistake, it’s not going to hurt the outside of your house or ruin the look. The downside is that it won’t last as long, and it might be more challenging to recoat with exterior paint.
The paint on your house will fade sooner than you’d like and will likely start to chip or peel away in the places that get the most rainfall. Interior paint wasn’t created for such conditions.
NOTE: You can repaint with exterior paint if you like or wait until it’s chipped. If you’ve only painted a little of your house before realizing your mistake, you can purchase exterior paint and cover the parts you’ve already painted before painting the rest of the house.
Do not leave the interior paint uncovered, even if it’s the same color. That paint will chip and fade faster, and your home will look uneven.
Can You Use Exterior Paint Inside?
You should avoid using exterior paint inside your house for similar reasons as using interior paint outdoors. Exterior paint is hardier and is meant for extreme temperatures and natural conditions. It may seem like it would make an indoor paint job last longer, but it has some health hazards.
The additives that keep the paint from solidifying in the paint can are called volatile organic compounds (VOCs). VOCs are in the color while it’s wet but evaporate as soon as the paint is on the walls. They become fumes that eventually clear out of a room when aired out and over time.
Exterior paints have more VOCs than interior paints to help the paint last longer in any weather. However, this also means that there are more fumes, and they don’t evaporate as quickly. The added chemicals in exterior paint make the paint last longer but could be dangerous to humans in enclosed spaces. It can cause lightheadedness and headaches.
NOTE: Even when rooms are adequately aired out, it’s vital to ensure safety and get a professional to check.
Also, exterior paint is more expensive, so it is much more practical to use interior paint for anything indoors.
What Happens if I Use Exterior Paint for Interior Use?
If you used exterior paint in an indoor space, the most important thing is to make sure the room airs out well enough. Because of the extra chemicals, the fumes will last longer and be more dangerous.
Once you’ve aired out the room and are sure there are no more fumes, you can use the room as usual.
The room that you painted with exterior paint will also not have the same clean, smooth finish as it would have with interior paint, though. It might also not do as well with regular wall cleanings and will have more scratches.
KEEP IN MIND: The room should handle the exterior paint, and you won’t have to repaint for quite some time.
Final Thoughts
Homeowners shouldn’t use interior paint outside or exterior paint inside. The chemical makeup of the paints does the best in the environment they were created for and shouldn’t be switched. For the best results when painting the interior or exterior of your house, use the proper kind of paint.
