To someone attempting their first paint job, all paints will essentially appear to be the same. There are finishes, like gloss, matte, eggshell and flat that you may more or less understand, but paint is just paint, right? As long as you get the colour right, what could go wrong?
You may be considering using exterior paint indoors. After all, it’s probably more durable, and it may come in the exact colour you are looking for. Can you paint indoors with an exterior paint though? What’s the difference between them?
Can You Use Exterior Paint Inside?
While you can in theory use exterior paint inside, it is definitely not recommended. Exterior paints contain VOCs that are unsafe for indoor use, as well as various binders and pigments that can make them especially toxic inside.
Exterior paints are meant to protect the outside of your home and last for a very long time, exposed to all kinds of elements, humidity and varied temperatures. The same is not true of indoor paints, which aren’t exposed to such harsh conditions.
These two types of paints are thus made differently. Exterior paints produce toxic fumes even after they have dried. They will keep off-gassing VOCs (volatile organic compounds, dangerous to inhale) until they are cured, which can take several weeks, or even months.
When used outside, the VOCs present no threat, as they don’t collect in a single room, and there is plenty of air to thin them out. They would be much more concentrated in a closed space, leaving you exposed to toxicity for an extended period of time, causing both short- and long-term issues.
Why Can’t You Use Exterior Paint Inside?
There are several reasons why you should never use exterior paint inside.
Off-Gassing While Drying and Curing
Paint has a specific, strong smell, caused by the VOCs it contains, among other things. A lot of modern indoor paints are VOC-free, and thus come without this smell.
Outdoor paints usually have a longer off-gassing period, meaning they will continue to smell and emit fumes for a week or even much longer.
While there is sufficient airflow outside not to make this an issue, the same can not be said for inside your home. Without sufficient ventilation, the VOCs can cause serious harm to your health.
Long-Term VOC Emission
While VOC emission is at its highest while a paint is drying and curing, it does not magically stop at the moment the paint is finally cured. It will still emit low levels of toxic fumes for a long time to come.
This is no problem outside, as there is more than sufficient airflow to prevent these compounds from causing any harm. Indoors, there is no reliable and easy way to ensure the VOC level is so low that it is rendered harmless.
Even if you were to move back into a room you’ve used exterior paint in several weeks after the paint job, there would still be some low-level VOC emission in it, which can be harmful in the long term.
Requires Sunlight to Cure
A lot of exterior paints require sunlight to cure properly. Even then, they may require several months.
If used indoors, exterior paints wouldn’t get the required amount of sunlight, the lack of which would make them cure even longer. During all of that time, they would keep emitting their toxic VOCs into your lungs.
Harmful Effects on Your Health
Exposure to the VOCs and other emissions from paint, especially exterior paint, can cause or worsen existing health problems. When used properly, these fumes are left outside where there is plenty of fresh air to counteract their negative effect.
When used indoors however, they will accumulate, and can cause issues ranging from headaches, eye, nose and throat irritation, loss of coordination and nausea. Long-term exposure can cause kidney and liver damage, potentially certain types of cancer and damage to your nervous system
Not Meant for Indoor Use
Exterior paint was not meant to be used indoors, and will adhere differently to drywall than to exterior brick or wood. It also comes in different finishes and textures, so you probably won’t be able to find the kinds that would fit your indoor needs.
Exterior paints contract and expand more easily, as they are supposed to withstand large temperature fluctuations. You don’t need this kind of flexibility indoors.
Exterior paints are also more prone to scrapes and stains, believe it or not. Their aim is to stand up to the weather, and not to a large amount of hands touching it, or extensive scratching.
Differences Between Exterior and Interior Paint
Exterior paint and interior paint are vastly different. Here’s how:
Interior Paints Don’t Actually Contain Latex
Even though a lot of interior paints are called latex paints, they don’t actually contain any of it. Exterior paints on the other hand do contain it, making it more weather-resistant and flexible, able to adapt to temperature changes.
Exterior Paints Take Longer to Cure
Exterior paints will take much longer to cure, sometimes weeks or even months. While they are doing so, they will be emitting VOCs and other gases, which are harmful to humans and pets.
These compounds are what makes exterior paint so durable and resilient. However, they aren’t required in interior paints.
Interior Paints Don’t Smell as Strongly
Interior paints are low-odour, and they can also be low- or zero-VOC. This will make them much more pleasant in the scent department, and they will not be as nausea-inducing.
Exterior Paints are High in VOCs
The VOCs used in exterior paint are what makes them so durable. However, they are toxic in an inclosed space. Indoor paints contain much fewer, if any harmful compounds, and will cure much faster, usually in a matter of days.
Interior Paints are Easier to Clean
Interior paints can easily be cleaned once dried, as manufacturers expect you to lean against your walls and touch them. Exterior paints will show marks and stains much quicker.
Is it Dangerous to Use Exterior Paint Indoors?
Yes, using exterior paint indoors can be dangerous due to the high VOC content of these paints. Don’t use exterior paint inside your home, as it can cause significant health issues.
Using exterior paint indoors will expose you and your family to the VOCs this paint is high in. It may take as much as six months for them to evaporate completely, during which time they will be slowly damaging your health.
The first symptom you will usually notice is dizziness or lightheadedness. You may also feel nausea, irritation in your nose and throat, and a worsening headache.
Respiratory disease and a weakened immune system will be the next side effect of using exterior paints indoors. Over the long term, there may be allergic reactions, kidney and liver issues, and even cancer.
When to Use Exterior Paint Indoors
Exterior paint shouldn’t be used indoors, unless you are painting a room that won’t be in use for several months, or if you are painting the inside of an outdoor building: garage, shed, cabana.
Due to the high emissions of exterior paints, you can safely use them indoors only if you want to paint a room that is never or very rarely occupied. This is unlikely to be a space in your actual home, but it may be a garage or a tool shed.
If you decide to use exterior paint in any indoor space, you must make sure it is extremely well ventilated for at least several weeks, and always open the windows when you enter it for the next several months.
Make sure no children or pets are able to get into this space, as they may not feel any discomfort once the majority of the fumes have evaporated, but the emission will remain high.
Can You Mix Interior and Exterior Paint?
While you can theoretically mix interior and exterior paints that have the same base, you should refrain from doing so, as you may end up wasting both of them.
These two types of paints have been formulated to work very differently, and they are a mixture of very different compounds. Mixing two oil-based or two latex-based paints is an option, but there is simply no reason to mix interior and exterior paint.
If you dilute exterior paint with interior paint, it may lose some of its durability and flexibility. The exterior paint will on the other hand add harmful VOCs to the interior paint, so you would end up with a mixture that doesn’t work well either indoors or outdoors.
Can You Use Exterior Paint In a Bathroom?
You shouldn’t use exterior paint in your bathroom as the high VOCs will be impossible to air out, meaning you will be exposed to toxic fumes for months.
You may be tempted to use an exterior paint in your bathroom as it works so well against fungus and mildew. However, the mere fact that your bathroom will smell like paint practically forever (in reality several months) and that you will be inhaling dangerous compounds as you shower should be reason enough to deter you.
Can You Use Exterior Paint on Kitchen Cabinets?
Exterior paints shouldn’t be used on kitchen cabinets, as they are high in VOCs that will keep off-gassing for months. This can cause long-term health issues, as well as immediate discomfort.
While exterior paints may appear the more durable solution, they are in fact not meant to be used indoors, under practically any circumstances. You can find a much safer, equally durable option for your cabinets.
Can You Use Exterior Latex Paint Inside?
You shouldn’t use exterior latex paints inside, as they produce harmful fumes that are toxic in the long-term.
Can You Use Exterior Paint on Furniture?
You can use exterior paint on exterior furniture. You shouldn’t use it on any indoor furniture, as the fumes will take months to evaporate, damaging your health all the time.
Can You Store Exterior Paint Indoors?
You can store exterior paint indoors, as long as you seal the container properly, and wipe away any smears and splatter from it. An improperly sealed container will still emit harmful VOCs.
Aim to store all of your paint in a room you don’t spend any time in: a garage, utility closet or basement.
Also make sure to mark the can to know when you’ve opened it, and what type of paint it is, if you’ve removed the label.
What Happens If You Use Exterior Paint Inside?
Using exterior paint inside may trigger allergic reactions, cause dizziness, lightheadedness and vomiting, and negatively affect you and your family’s health in the long term.
Breathing in the VOCs that exterior paint emits is not healthy for humans or pets. If you spend time in a room where exterior paint has been used, you will soon start to feel the negative effects, and can over time start to get seriously ill.
Exterior paints will also not be as durable indoors, so you may start to see scratches and stains much sooner than you would like.
What to Do If You Use Exterior Paint Inside?
If you have used exterior paint indoors, make sure to keep the space well ventilated and to spend as little time in it as possible.
It will take months for all the VOCs from exterior paint to completely evaporate. While this is happening, you are advised to spend as little time in that room as possible, and to cover your mouth and nose if you have to be there.
Keep the windows open as often as possible, especially during the night, and install ventilators to get the air moving. While this will help reduce the fumes and the smell, it won’t solve the VOC problem overnight.
Wrapping It Up
Don’t use exterior paint indoors if you can help it, unless you are painting a garage or basement. Even then, only use these paints if you can easily air the space and ensure that the toxic fumes evaporate as quickly as possible.