You bought the wrong can of paint, or you have a leftover can that you don’t want to waste. Unfortunately, you have exterior paint but you need to paint your inner walls. Can you still use it?
Can you use exterior paint inside? While there are some cases when you can safely use exterior paint indoors, it is not recommended. It emits fumes that can cause allergies and respiratory problems, such as Volatile Organic Compounds (VOCs), pigments, binders, and additives.
What is the Difference Between Exterior and Interior Paint?
Exterior paint is designed to withstand harsh weather conditions and extreme changes in temperature. However, its materials take longer to cure, have a strong odor, and can cause side effects when inhaled.
Exterior paints will usually contain latex, binders, and additives. These ingredients like increase the durability and flexibility of the paint, so it doesn’t buckle, crack or fade despite being exposed to the heat of the sun.
These additives are also water-resistant, to protect it from rain and snow, and the natural moisture in the air.
Advanced formulas may also contain UV blockers and fungicides that prevent mold, rot and mildew from developing on the walls.
Unfortunately, exterior paint takes longer to dry or cure, and the paint emits fumes for several weeks after application. The strong odor can also linger for days. However, manufacturers assume that it will not be a safety issue because the paint will dry in open air—it does not pose a safety risk to construction workers and the homeowners.
Indoor paints are designed with safety in mind. Manufacturers anticipate that workers will apply this in an enclosed environment, and even homeowners may do periodic makeovers while they are living in the house.
With that in mind, indoor paints contain ingredients that do not emit toxic fumes and are low in odor. It is also formulated to dry faster, even if it means that it is less durable than exterior paints.
More premium indoor paint formulas are also designed to be easy to clean and resist stains, or have special finishes or colors that aren’t available in exterior paints. Again, this is a reflection of how manufacturers anticipate what buyers want and need from their paint.
What are the Dangers of Inhaling the Fumes of Exterior Paint?
Exposure and inhalation to exterior paint fumes can cause dizziness and lightheadedness, headaches, and nausea and side effects. If you are sensitive to the paint, have respiratory conditions like asthma, you may also have difficulty breathing.
Continuous, long-term exposure to toxic fumes can also damage the lungs, liver, kidney, and nervous system, and can increase the risk for some kinds of cancer.
That is why safety regulations require workers to wear protective masks, respirators, and gloves when handling exterior paint—even in outdoor spaces.
All cans of exterior paint also have the warning not to use it indoors, so if you choose to use it you are essentially accepting the responsibility for any possible health risks to you, your family, and your pets.
How Long Will it Take for Toxic Fumes and Strong Paint Smells to Go Away?
It can take 2 to 3 days for the paint smell to go away, but fumes can continue to disperse into the air for much longer than that. Stronger exterior paint formulas may even emit fumes for up to six months.
The fumes and toxicity levels increase enclosed indoor areas—reaching up to 10 times more than open, outdoor areas. So even if you use indoor paint, experts still recommending waiting about 2 or 3 days before using the room.
What Will Happen if You Use Exterior Paint for Interior Walls?
Aside from exposing your family to toxic fumes and the health risks involved, you may actually be unhappy with the results of your paint job.
Exterior paints are more flexible and stretchy in order to become weather-resistant. However, this quality also makes them softer and more prone to stains and scratches. So, you may end up repainting the walls sooner than expected, and spending more than if you bought indoor paint from the beginning.
What Situations Can You Consider Using Exterior Paint for Interior Walls?
It is always best to use interior paint for interior walls, but there are some situations when you can use exterior paint with a little less risk.
Painting an Outdoor Building
You may use exterior paint if the building is detached and rarely occupied for long periods of time. Examples include a storage shed, garden shed, pool-side cabanas, or a garage.
Room Will Not be Used for a Few Months
If you are willing to wait it out and leave the room unused for several months, then you can use exterior paint.
For example, you can repaint a vacation home at the end of your stay, knowing that the fumes would have long dissipated by the time you return the next year.
Room Has A Lot of Ventilation
Ventilation is critical so that anyone who is panting the room won’t be exposed to very high levels of toxic fumes.
There should be a lot of large windows and an exhaust fan. Be sure to wear respirators and masks, and take frequent breaks for fresh air. Stop painting if you notice signs of dizziness, lightheadedness or nausea.
Given this, anticipate that when you use exterior paint indoors, you will have to allot more time to complete the job. You can’t rush the process and compromise your safety and health.
If you want the paint job to be done as quickly as possible, it’s better to use interior paint—which not only emits less fumes, but also dries faster.
The Verdict: Can You Use Exterior Paint for Indoors
If possible, always choose the right paint formula for the project: exterior paint for exterior walls, interior paint for interior walls. You are guaranteed of the quality and safety, and can expect to get the best results.
You may use exterior paint indoors if you are willing to wait several months, if there is proper ventilation and safety precaution, and if the room is detached from the main area.
