Can You Use Exterior Paint Inside? (A Warning!)

Buying paint can end up proving pretty costly, especially if you’re painting a large room.

Sometimes it can be tempting to use any leftover exterior paint for painting inside your house to cut down the costs.

Whilst there are no strict rules as to whether you should use exterior paint indoors, there are some reasons why you should definitely stick to using it outdoors in the future. 

Because in most cases interior paints and exterior paints are different and the chemicals contained in one can suit outdoors but be more harmful when used indoors. 

So, can you use exterior paint inside? Here's why it's probably not a good idea...

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The difference between exterior and interior paints?

You may think that there is not much difference between the two, however, both interior paint and exterior paint have different formulations to perform different jobs.

Exterior paints are formulated to withstand all weather conditions.

They are very water-resistant to keep away mold and they also contain flexible acrylic resins that change in size depending on fluctuating temperature outdoors.

They also contain ultraviolet blocking properties which will stop the paint from fading in the sunlight. 

You do not need these properties inside your home so indoor paint is formulated differently.

They are made to withstand all the bumps and scrapes that occur from furniture, people, and general day to day life.

Interior paint is often smoother in appearance and looks better on the walls.

Interior paints are also available in various finishes which can all differ in durability abilities. 

You may still be convinced that using exterior paint in rooms such as your bathroom will be more beneficial in the long run as it will prevent mildew or peeling that has been caused by moisture.

However, this is not the answer, bathrooms tend to be a lot smaller and will take a while to ventilate if you haven’t got a window.

An easier solution to prevent the build-up of moisture would be investing in a good bathroom fan that you should keep on during and 20 minutes after showering to make sure all moisture is gone.

If you’ve got the extra expenses, you could always get a window built-in to your bathroom. 

Exterior paint about to be used to paint inside

Health risks of using exterior paint inside

Modern-day indoor paint is made to produce very little or no paint fumes at all. However, paints that are made to be used outdoors contain lots of VOC (volatile organic compounds) or more commonly known as paint fumes.

VOCs are present in exterior paint because it holds the pigmentation of the paint and secures it to the walls outside.

These fumes can emit into the air and can be sometimes undisguisable to the human nose. VOC’s are bad for the environment as it plays a significant role in the ozone layer. 

Once you consider what it’s doing for the environment then you’ll be dead against using it within the compounds of your own home. 

Using the exterior paint indoors will make the air linger with VOCs and other harmful chemicals for a long time. It’s not just the odor that is the problem, but the health problems it can cause you for not only you but your pets as well.

The chemicals emitting from the paint can cause dry eyes and an itchy throat, especially if you are spending a lot of time in that room.

VOCs have been known to cause further issues for people who suffer from respiratory problems and can make it very difficult to breathe properly. 

The VOCs from exterior paint can also cause other side effects like light headedness, nausea, and even vomiting in some cases.

If you have very sensitive skin, then the chemicals from the paint can cause you to come out in a rash.

Heavy concentrations of VOCs or long term exposure can lead to very serious health implications like liver damage or even cancer.

If you plan on airing the room by windows and doors out after using exterior paint, it will still take a long time to completely get rid of the odor and eradicate harmful VOCs. 

Getting rid of an exterior paint job inside

If you’ve already gone and painted the inside of your house with exterior paint and now contemplating undoing it then it is possible but will take a bit of time. You’ll need to completely remove and scrape all the exterior paint off first.

Sand it down and then wash your walls with a sponge and warm soapy water or you could even specialized sugar soap to clean it thoroughly.  

You’ll have to make sure the wall is completely dry before moving on to the next part.

Use a primer all over the walls and wait for it to dry before painting, this could take from 30 minutes to 3 hours depending on the humidity levels in your home.

The primer will now act as a barrier to the fumes from the exterior paint (see also: What Kind Of Paint Is Used In Hydro Dipping?). You’ll now be able to start with your indoor paint.

Just painting over exterior paint with paint intended for indoor use will not eliminate the odor or VOCs in the air. 

Ventilating a room when using exterior paint indoors

As exterior paint does hold more durability and moisture-resistant properties than indoor paint, we do understand that sometimes it just makes sense to use it inside.

If you plan on going ahead with using it inside then make sure you ventilate your room throughout.

Whilst you are painting you should keep all your windows and doors open to let the fumes out, you’ll need to buy or hire out heavy-duty fans that will be able to increase airflow and push the chemicals out through open windows or doors.

You’ll want to use the appropriate breathing apparatus whilst you are painting like a respirator you can wear to cover your nose and mouth or even a full face mask to stop you from inhaling the chemicals. 

When you’re not painting, leave any open tins of paint outside and not in the room or keep the lid firmly sealed.

If the room you’re painting has doors leading to other rooms, keep them closed overnight, open up the windows and keep the fans on as long as possible to completely ventilate the room. 

You’ll probably need to wait 2-3 days, however, if you’re not ventilating the room with fans you may need to wait longer before you can use the room again. 

We hope this answered any questions surrounding using exterior paints indoors. Whilst we do not recommend you using it, it is not totally impossible to do so.

If you are going to use exterior paint inside your home, you should do as at your discretion and follow our health and safety recommendations.