Can You Use Exterior Paint Inside? (Why You Shouldn’t)

All paints are made from the same four kinds of ingredients. The different colors come from pigments, which are created from plants, animal matter, minerals, or synthetic material.  

Additives like thickeners or chemicals will give it a shiny or matte finish and may add extra protection against things like fungus. Flexible acrylic resins bind up the pigments and make the paint stick where it is painted. 

Solvents like water, turpentine, or mineral spirits bring these components together and dissolve them into a liquid. As the paint dries, this solvent evaporates. 

When it comes to interior vs exterior paint, exterior paints may contain different kinds of additives than interior paint, as it will need to deal with different indoor environments factors. 

Outside areas will encounter rain, snow, direct sunlight, high winds, mildew, fungus, and more. Changes in temperature or direct sunlight may make the paint expand or contract, so the acrylic resins in exterior paint are flexible enough to cope with this.  

The additives can combat UV damage and fading, mildew, and fungus. There is often less range with exterior paint finishes. It's usual to only find gloss enamel, semi-gloss, or flat exterior paint. 

Exterior paint resilient outdoors may also emit more volatile organic compounds (VOCs) due to the harsher additives needed. This is one reason why exterior paints should not be used indoors. Most exterior paints tend to be water rather than oil-based. 

Oil-based paints can release VOCs that are harmful to the environment, and some states have banned their use by law.  

Interior paints or paint designed to be easy to clean and more weather resistant to scuffs and marks. Interior paint can sometimes contain plastic to give them a smoother finish, which also helps make interior paint easy to clean and resist dust.  

It’s not usual for interior paints to need additives such as fungicide, and they should also emit less VOCs than most exterior paint. Their range of finishes is much wider, with interior paints such as eggshell, gloss, satin, and even some faux-finish interior paints.  

It's tempting to want to use exterior paint inside, especially if you're in the middle of a big project. You may think it will save time and money, but to use exterior paint inside is not a good idea.  

The ingredients that help most exterior paint do a great job in keeping the outside of your house looking bright are the very reason you shouldn’t risk using this paint indoors.

The chemicals in these exterior paints can be harmful to people, especially if you’re regularly in a poorly ventilated room with them.

Exterior paint gives off more VOCs due to the chemicals in them. Therefore, any areas where these exterior paints are used should be well ventilated - ideally completely outdoors! 

Being exposed to VOCs can lead to lightheadedness and nausea and should be avoided especially by pregnant women, children, and pets. 

If use exterior paint inside also has a stronger smell (another side effect of the VOCs) which may linger long after it has dried. Places with poor ventilation will be affected more.

Any exterior paints that are oil-based may be flammable, which is not a desirable feature for any paint used inside the house. 

Because of its more specialist ingredients, exterior paint costs more. You may think it will save money to use up all the paint, but it’s better saved for an area that will actually benefit.

Indoor spaces or confined spaces don’t need protection from the extreme weather fluctuations or changing temperatures and challenging outdoor conditions. 

You can use exterior paint indoors, but you really shouldn't. As the reasons above explain, it's not safe due to the ingredients of exterior paint, and it's not recommended by experts.   

However, if you are determined to do so, follow these tips to be as safe as possible. 

Open all windows and doors, use fans and any other indoor air quality filtration equipment you have available to reduce the effects of the paint fumes or toxic fumes and VOCs. The room should be ventilated while painting and for at least two or three days afterward. 

This is standard even when using interior paints, so it may be wise to leave it longer when using exterior paint, as the odor can linger in less ventilated areas for months.

Again, when working with acrylic latex, masks should always be used, as should outerwear to protect your clothes and gloves to protect your hands. 

If possible, leaving the house well-ventilated and empty for several days while it dries could be a good way to prevent yourself from inhaling too many VOCs.

The biggest reason not to use exterior paint indoors is the volatile organic compounds that can be emitted.

In outdoor paint areas, there is enough ventilation that there shouldn’t be too much risk to health, but in a more concentrated indoor paint area, especially a room you use often, the health risks are increased.  

Over-exposure to VOCs could cause symptoms such as headache, breathlessness, fatigue, nausea, skin problems, and dizziness. You can have eye, nose, and throat irritations, and even lung irritations.

Extreme cases can see damage to the central nervous system, liver, or kidney. Saving a few extra dollars is really not worth the risk! 

If this warning is coming a little too late, here are some tips for making your house as safe as possible if you already use exterior paint inside. 

Garages may feel like the exception to the interior/exterior debate. They can be enclosed on four sides, but one of these sides can typically be completely opened, exposing it to the outside and its weather changes.

It may seem tempting to opt for an exterior paint that will withstand all the activities you may use your garage for.  

Exterior paint is still not recommended for garages as they are still interior spaces, but due to the large garage doors, it is safer to use exterior paint here. Exterior acrylic latex paint is a great option for a garage, as premium latex exterior paint is easier to clean, dries quickly, and works better on rugged walls.  

Interior and exterior paints have the same basic components and could, in theory, be combined, but still should never be mixed. Strong VOCs make exterior paint unsuitable for use indoors, and combining interior paint and exterior paint would increase the amount of VOCs the acrylic latex might emit.  

Using interior paint outdoors or interior paint on the exterior of the house won't work as it isn’t created to deal with weather, mildew, and aging like exterior paint, so mixing the two would make the exterior and interior paint useless both inside and out.

It may also not be a good idea as exterior paints indoors can be oil paints, whereas interior paints are usually water based, as these two types don’t mix well.  

It’s important to follow the correct guidelines when applying exterior paints indoors on your house. If done improperly, you may damage your home, yourself, and your bank account.

For many of us, the best solution may be to hire a professional. But should you be attempting it yourself, always buy the best materials possible. The better quality primer and exterior paints, the longer they will last.  

Prepare the exterior surfaces before painting by cleaning it and ensuring exterior paints or outdoor paints dry and not flaking. Old paint may need to be scraped or sanded first.

Avoid any paint containing lead, cover any nearby areas or furniture that may be sprayed or splattered with paint, and be sure to apply the paint with the most appropriate tools, whether that’s a sprayer or a roller. It’s always best to paint outside when you have good weather! 

A fresh coat of masonry paint brightens up any home, both exterior and interior paint, but always ensure the materials you choose are the right ones for your project!

Interior and exterior paints are intended for very different purposes.