Are you wondering if you can use leftover interior paint on an exterior surface?
Or maybe you have a surplus of exterior paint and are curious whether it’s safe to use indoors?
In this comparison of interior vs. exterior paint, you’ll learn:
- The key differences between interior and exterior paint
- The risks of using interior paint outside and exterior paint inside
- And what to do if you already used the wrong paint type.
By the end, you’ll have all the knowledge needed to decide whether to use the paint you have or pick up an alternative option.
Use the links below to navigate:
- Interior Paint: A Quick Overview
- Exterior Paint: A Quick Overview
- Can You Use Interior Paint Outside?
- Can You Use Exterior Paint Inside?
- What to Do If You Already Used Interior Paint Outside
- What to Do If You Already Used Exterior Paint Inside
- Hybrid Paints Can Be Used Inside and Outside
- Final Thoughts
Interior Paint: A Quick Overview
Interior paint is designed to withstand pets, furniture, vacuums, and everything else that rubs against it on a daily basis. It resists staining, fading, and yellowing, and can be wiped and scrubbed when it gets dirty.
It’s usually water-based (also referred to as latex) rather than oil-based, and made up of four basic compounds: pigments, solvents, additives, and resins.
Compared to exterior paint, interior paint uses more rigid resins, which leads to easier cleanup and stain resistance.
It also contains specific additives to reduce drying time and distribute pigment evenly.
Unlike exterior paint, interior paint doesn’t have weather-proofing additives.
Another key characteristic of interior paint is that it produces less odor due to a smaller amount of VOCs (volatile organic compounds) than exterior paint.
What are VOCs?
VOCs are chemical gases that release into the air as the paint dries.
Have you ever got a headache or dizziness after being near paint for long periods? That’s a result of extended exposure to VOCs.
Since interior paint is designed for indoor use where the air circulation is limited, most have low VOCs, and you can even find no-VOC interior paint.
Exterior Paint: A Quick Overview
In the past, most exterior paints were oil-based because it provided a more durable finish. But, thanks to advances in technology, the trend has switched. Now, most exterior paint is water-based with acrylic resins to aid in binding.
The most significant difference between interior paint and exterior paint is that exterior paint has more additives to withstand the outdoor elements.
Exterior paint has to be able to resist moisture from rain, snow, and wind. It needs to tolerate both temperature drops and quick increases and maintain its color hue even after hours in the sun.
Exterior paint contains softer and more flexible resins, which help it resist mildew, peeling, and chipping. That flexibility allows it to contract when exposed to moisture.
Can You Use Interior Paint Outside?
The short answer is no. Interior paints should not be used outside because they lack the additives necessary to withstand the outdoor elements.
But, besides the durability concerns, interior paint is thinner than exterior paint, so it doesn’t adhere well to exterior surfaces, and you’d need apply additional coats to achieve the same coverage. Even with multiple coats, it won’t look as even as it would with exterior paint.
Lastly, it takes longer for interior paint to dry since it’s not designed to dry in outdoor elements.
Even if you manage to get decent coverage with interior paint, the job is not done. Over time, you’ll notice that interior paint on outdoor surfaces will fade and crack, forcing you to do touch-ups more frequently.
Can You Use Exterior Paint Inside?
No, you should never use exterior paint inside. Due to its chemical makeup, it’s extremely dangerous to use exterior paint inside your home.
When you use exterior paint indoors, you expose yourself to chemical fumes, VOCs, mildewcides, and other potentially hazardous ingredients in an enclosed space.
In poorly ventilated rooms, these chemicals hang in the air and irritate your skin and respiratory system.
Even after the paint has cured, it continues to release VOCs. In fact, you may be able to smell the mildewcides and fungicides in the paint weeks or months later if the weather is humid, which can trigger allergies and cause irritation.
Alternatively, interior paint has the fewest amount of VOCs. You can even find interior paint with no VOCs at all. Typically, the VOCs should vaporize at room temperature and can be ventilated via open windows.
There are some exemptions to the rule. Though this shouldn’t be your first choice, you can use exterior paint in sheds, detached garages, or other detached areas where nobody sleeps or spends long periods of time.
What to Do If You Already Used Interior Paint Outside
If you’ve already used interior paint outside, there’s no need to panic. Just know that it won’t last very long. The reality is, interior paint isn’t made to withstand harsh weather elements, and you’ll soon notice fading, peeling, and flaking.
Once it starts to wear away, you’ll most likely have to sand, re-prime, and repaint the whole surface. This is a big job and one you want to avoid.
Therefore, if you’ve already painted an outdoor surface with interior paint, brush a quick layer of exterior paint over it.
You may need to sand off any cracked or peeled bits and prime these areas before applying exterior paint. While this is annoying, it’s the best way to ensure the surface looks pristine.
The truth is, using interior paint outside can end up being a costly mistake. To fix it, you need to take time out of your day and buy new products to rectify the error.
What to Do If You Already Used Exterior Paint Inside
If you already used exterior paint inside, it’s a much more problematic situation, given the health hazards.
First, ventilate the room by opening windows, especially while the paint is drying. Stay out of the room as much as possible for a few weeks while the paint cures. If it’s cold outside, this may take a few months.
If you’ve used an oil-based paint and want to repaint the area, sand the wall down first before applying a new coat of interior paint.
Hybrid Paints Can Be Used Inside and Outside
If you’re looking for flexibility, consider purchasing hybrid paints (like this one on Amazon), which can be used indoors and outdoors.
However, these are convenient paints and aren’t as effective as interior or exterior paints. They lack some of the necessary ingredients and additives, especially for outdoor usage.
Don’t expect the same kind of mildew, moisture, and cracking protection of traditional exterior paint.
Overall, hybrid paints are best for smaller projects, and they perform better inside than outside.
Here’s the takeaway: each paint type is meant for a specific purpose. Adhere to that guidance. Using interior paint outdoors will require frequent touch-ups since it can’t withstand harsh weather elements.
And using exterior paint indoors is a big no-no. The paint fumes, chemical makeup, and VOCs are a health hazard, often leading to skin and respiratory irritation.
If you’re stuck in a situation where you have leftover paint, there are fun and easy ways to put it to use, so you don’t waste it. For leftover interior paint, try using it for crafts, upcycling an old piece of furniture, or touching up previous paint jobs.
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