Before you use outside paints inside of interior spaces, read this article first! Learn which paints may be applied where and why, as well as how and why not.
Deciding which paint to use when you paint the walls inside your home can be overwhelming with the number of colors, finishes, and brands to choose from. If the can of paint you settle on has the label “exterior paint” rather than “interior paint”, can you still use exterior paint inside?
As a general rule, exterior paint should not be used to paint the inside of your house. Using exterior paint indoors would allow the chemical fumes used in exterior paint to resist UV rays, harmful volatile organic compounds or VOCs, and other toxic fumes to build up in the closed space.
I hate to disrupt anyone’s DIY project with unfortunate news, and I’m sure you’re asking yourself “But can I really not use exterior paint inside, no matter what I try? Not even my kitchen cabinets?” If you’re still wondering what exactly makes exterior paint dangerous, you are about to find out.
Can I Use Exterior Paint Inside My House?
It honestly doesn’t matter what you try to do to paint the interior of your home with paints intended to be used outside only. Using exterior paint in the interior or confined spaces will only promote the accumulation of dangerous, toxic fumes that have the potential to make you and anyone else in the building sick.
Exterior paint has different additives from interior paint, and the chemical mixture’s intended purpose is to be weather resistant, damaging UV rays caused by direct sunlight, and harmful VOCs. VOCs, volatile organic compounds, are not always dangerous but they ones that have the potential to cause cancer. This is why it’s important to pay attention to the paints you’re putting on your walls, especially interior walls.
“If exterior paint contains harmful VOCs and other chemicals, why do we use it at all?”
The reason we can use exterior paint outdoors is because of the open air. As you can imagine, rooms in our homes or other buildings suffer from poor ventilation. Most of the air that we breathe sits around in the buildings, unable to refresh without proper ventilation. The toxic fumes don’t have the opportunity to accumulate or build up in a way that affects anyone’s health in any way.
Don’t bother trying to open windows and set up fans to get good ventilation after using exterior paint indoors because exterior paint can still give off dangerous fumes even after it dries! Even paints made with a water-based formula, an oil-based formula, and acrylic latex paints contain those potentially dangerous paint fumes that get into the air that we breathe.
You shouldn’t even use exterior paint inside a covered porch. Your windows, if you have enough, won’t be open all year round to provide the proper ventilation needed to outweigh the risk factor.
To give you a definite answer you can’t ignore: you should never use exterior paint indoors! If you use exterior paint in paint sprayers that you later plan to use to paint inside, wash them thoroughly! Once you use exterior paint indoors, the damage is done.
What is the Difference Between Interior and Exterior Paint?
You’ve learned a little bit about the different ingredients in interior paint and exterior paint, but what exactly are those ingredients? Why do exterior paints use them?
Exterior paints for homes and other buildings are mixed differently than paint designed for the interior of buildings. They have extra compounds and additives to last longer and resist natural elements that cause paint to deteriorate and fade on outdoor surfaces. Exterior paint is highly water resistant to prevent damage from rain, resistant to UV rays that come from direct sunlight (ultraviolet radiation that penetrates the atmosphere and reaches the earth), and even to dirt!
We already talked about VOCs, and how some volatile organic compounds have the potential to be very dangerous. This is especially true for people with sensitivities, allergies, or issues breathing – whether or not you’re aware you have them or not. To know more about them, check out an article published by brewers.co.uk, “What are VOCs and what are they used for?”
Exterior oil-based paints contain something called alkyd. Alkyds are synthetic polyester resins that are used in not only paints but varnishes and adhesives as well. They’re made from acids and alcohol and have a thicker finish than the average acrylic latex paint. This is the exterior paint ingredient that makes it easier to clean things like dirt or other messes off the side of your house.
Fungicides and mildewcides are pesticides used to fight off fungi and mildew. It’s a lot of ‘cides’, I know, but it is important to know that these chemicals are used in exterior paint to resist any damage fungi and mildew can cause. You’ve probably already come to the conclusion that these pesticides aren’t the best thing for us to inhale.
Can Interior Paint Be Used As Outdoor Paint?
Although exterior paint can’t be used inside, both interior and exterior paint can be used as outdoor paint. That doesn’t particularly mean you should always use indoor paint as exterior paint, but you won’t have the same concerns about paint fumes. Professionals created a paint designed to resist the elements that people previously battled with when it came to exterior paint, and interior paint lacks those respective compounds.
When applied indoors, interior paint is not subject to weather damage or sun rays and it certainly isn’t equipped to handle them. Interior paint is definitely okay for outdoor use but, if you do use interior paint outdoors, expect to be touching up in as little as one year after application. However, if you’re in a tight spot and don’t have many choices, interior paint is a good option for a quick but temporary fix.
Can Exterior Paint Primer Be Coated Over Interior Paint?
Like with exterior paint, exterior paint primer should not be used to prime interior paint. Unlike siding, shingles, and other materials used on outdoor surfaces, interior walls are made of drywall, which is a very porous surface that will absorb whatever you put on it. However, it doesn’t absorb substances evenly, making the end product of paint and primer applications appear uneven and sloppy.
Exterior paint primer is also made with a different mixture than interior paints and primers that will give off paint fumes significantly more dangerous than what you’ll find in a normal paint primer, meaning it is not permitted for indoor use.
What is the Difference Between Interior and Exterior Paint Primer?
Other than the quality of interior walls and chemicals that make using exterior paint primer inside a bad idea, interior and exterior paint primers were created with specific intentions and attributes so that they excel in their reserved areas. If we know the main difference between interior paint and exterior paint is the chemical compounds, what makes interior paint primer different from exterior paint primer?
Primers are generally made out of the same base but further customized to fit the needs of interior use and exterior use, just like with interior and exterior paints. The main intention with interior primer is to create a consistent and smooth surface, as well as seal the paint underneath to prevent scrapes and scratches, and increase the adhesiveness. Do check homedepot.com for a list of primers to use.
When it comes to exterior paint primers, the purpose is a bit different. Indoor surfaces are not subject to the same factors as outdoor surfaces, therefore the primers and paints intended for outside use need to be much stronger and more resilient – there are even three specific categories of paint types to choose from. The general qualities of exterior paint primer are resistance to mildew, like with exterior paints, and cracking.
Both primers are meant to protect the surfaces they are painted over, but exterior paint primers do double the job on surfaces like wood, metal, and masonry because they are particularly susceptible to alkaline effects.
Outdoor paint is meant for outdoor use only, never indoor use, so do not use exterior paint indoors, whether you’re talking regular paint or paint primer. Visit lowes.com for a paint guide on exteriors.