Exterior paints are generally tougher than interior paints. Therefore, it can be tempting to want to use them indoors. But that is a bad idea.

You should never use exterior paints inside because they contain high concentrations of VOCs and other dangerous chemicals. Using them indoors could lead to severe allergic reactions and health problems. There is also the fact that they are more expensive than interior paints. And they generally don’t have as great a finish as that of interior paints.

Here is what you should know about the reasons why it is a bad idea to use exterior paints inside.

What makes indoor paints ideal for use inside the home?

Indoor paints are more suitable for use inside your home mainly because they are safer.

Low on VOCs

VOC’s are Volatile Organic Compounds and indoor paints are intentionally made with lower concentrations of VOCs. This is because these compounds are potentially harmful. They can also trigger severe allergic reactions in loved ones.
Therefore, indoor paints are ideal for use inside your home because they are safer for your loved ones.

 

Have weaker smells

The combination of fungicides, high concentration of VOCs, and resins in outdoor paints give them a strong smell. This isn’t a problem that you will face when using indoor paints because they don’t need the buffering that these compounds provide — they aren’t constantly exposed to external weather elements

 

Are scratch resistant

Even though indoor paints are poor at withstanding external weather elements, they are pretty good at withstanding the physical abuse of constant traffic. They are thus less likely to scratch.

 

Are generally cheaper

While indoor paint costs vary widely, these paints are generally cheaper than outdoor paints. As a result, painting inside your home with the appropriate paint will be kinder to your bank account.

 

Have better finishes for interiors

Indoor paints have smoother finishes. They are perfect for painting surfaces that you will be in close contact with. Therefore, if you want your home to look great, they are the obvious choice.

What are the symptoms of VOC exposure?

VOCs are active chemicals contained in most paints. When breathed in, they are known to cause the following symptoms.

  1. Headaches
  2. Eye irritation
  3. Nausea
  4. Dizziness
  5. Coughing
  6. Wheezing
  7. Difficulty breathing
  8. Allergic reactions
  9. Respiratory complications

Therefore, if you use outdoor paints inside your home and you or your loved ones start experiencing any of the above symptoms, the paint is to blame.

What should you do if you have already used exterior paint inside?

If you have already used exterior paint in your home, there are things that you can do to mitigate the effects of these paints.

Here are the most effective tips for countering the negative effects of outdoor paints inside a home.

Improve ventilation in your home

Improving airflow inside your home will increase the rate at which the toxic fumes from the paint flow out of your home. This means opening doors and windows. Investing in a good fan will also help.

And with fresh air constantly flowing into the home, it will also decrease the concentration of VOCs in the air, and this will reduce their overall effect on anyone who breathes them.

Remove anyone who is affected from the home

Fungicides and other compounds that are added to exterior paints to improve their toughness can trigger allergic reactions in loved ones.

If anyone inside your home starts coughing, experiences lightheadedness or headaches, the best thing that you can do for them is to remove them from the home.

Taking them outside will reduce the number of allergens to which they are exposed. And this will help to alleviate their symptoms.

Cover by painting over the old paint

Exterior paints are not ideal for indoor use because they release VOCs into your home. You can reduce the rate at which they do this by simply applying an extra coat of paint over the existing paint.

While doing so won’t completely eliminate the toxic compounds from your home, it will reduce the rate at which they are released into your home. This is because the exterior paint will be covered and shielded from your home’s air, and so it won’t have a chance to easily release these compounds.

Remove and repaint

If the paint is already having a negative impact on the health of your loved ones, especially after improving the ventilation of your home, then you should consider removing the paint.

Removing the paint will reduce the concentration of allergens in your home. And repainting the surfaces with paints that are meant for indoor use will restore the aesthetic appeal of your interior walls and other surfaces.

What happens if you use exterior paint for the interior?

If you use exterior paint on your home’s interior, you will start noticing any of the following.

Painted surfaces will scratch easily

While exterior paints are built to withstand weather elements, they are not great at resisting scratching. This is because they are not designed to withstand the traffic and abuse that most painted surfaces inside a home are usually subjected to.

Therefore, surfaces that are painted with exterior paints are bound to have more scratch marks than those that were coated with interior paints.

Your painting costs will increase

Exterior paints are generally more expensive than interior paints. This is because they contain additives and compounds that are designed to make them less susceptible to getting damaged by weather elements.

Therefore, since interior paints are cheaper, you are bound to notice a spike in your painting costs once you switch to exterior paints.

Your loved ones will start experiencing headaches, lightheadedness, or breathing problems

Exterior paints contain levels of VOCs that are not suitable for indoor use. Using them inside your home will therefore expose your loved ones to unsafe levels of these compounds.

Your loved ones are thus likely to experience common symptoms of VOC exposure that include headaches, nausea, breathing difficulties, and respiratory complications.

Visible allergic reactions in some of your loved ones

Exterior paints contain additives and other chemicals that are designed to make them resistant to mold and mildew. Unfortunately, these chemicals and additives can trigger allergic reactions in some people. And so it is not unusual for some people to experience skin irritation, eye irritation, and other common signs of allergies.

What is the difference between outside and inside paint?

The main difference between outside and inside paints lies in the type and concentrations of chemicals that they contain. The following is a table detailing the major differences between the two types of paints.

Exterior PaintsInterior Paints
Contain higher concentrations of VOCsContain lower concentrations of VOCs
Contain softer binding resinsContain rigid binding resins
They catch stains easily and are not as easy to cleanStain-resistant and easy to clean
More susceptible to scratching Has better resistance to scratching
Relatively pricierIt is cheaper than exterior paints
It is better at withstanding weather elements Don’t hold up as effectively when exposed to moisture, direct sunlight, and other environmental elements
Has an inferior finishHas a smoother finish

Is exterior paint more durable than interior?

Yes, exterior paints are generally more durable than interior paints. This is because they contain softer resins and higher concentrations of VOCs. As a result, they tend to be better at resisting moisture, withstanding extreme temperature changes, and fading.

The extra additives that these paints contain also make them less likely to fade. They also give them the ability to resist mildew and mold. And as far as chipping and peeling resistance is concerned, they are way better than interior paints.

However, when it comes to scratch resistance, interior paints have an edge over exterior paints.

Can you use exterior paint for interior trim?

It is inadvisable to use exterior paint on inside trim simply because doing so will compromise your home’s indoor air quality.
While exterior paints have better binders, they tend to have high concentrations of VOCs.

Therefore, using them inside your home will expose your loved ones to these chemicals.

Can I use interior paint outside if I seal it?

Even though sealing can help to prolong the lifespan of interior paints, it is still inadvisable to use them outside. This is because these paints don’t have the binders, resins, and other chemical concentrations that are necessary to allow them to withstand extreme temperature changes, constant moisture exposure, and sunlight.

Furthermore, these paints lack mildewcides and other compounds that give them a longer lifespan.

Therefore, even with a sealant, interior paint is still likely to chalk, fade or peel prematurely — when compared to exterior paints.

Should I use interior or exterior paint in my garage?

You should always use interior paint in your garage. Most garages are enclosed, and so using interior paints is safer since these paints contain lower levels of VOCs. And given that they are also easy to clean, more resistant to scratching, and dry up quickly, interior paints are perfect for garages.

You should never use exterior paints in your garage because they will compromise the air quality in the garage. And since most garages are enclosed — and thus shielded from environmental elements –, any benefits that exterior paints might have will be of little to no benefit.

Is exterior paint more expensive than interior paint?

Yes, exterior paints are generally more expensive than interior paints. This is mainly because they contain extra compounds and additives that are designed to make them better at withstanding extreme temperatures, constant moisture exposure, mildew growth, and sunlight.

FAQ's

Yes, there is a big difference between interior and exterior paints.

While exterior paints are designed to withstand the external environment, interior paints are designed to be both scratch-resistant and easy to clean. As a result, they differ in terms of their chemical makeup.

For example, exterior paints contain higher concentrations of VOCs. They also contain chemicals like mildewcides. And they tend to be more resistant to fading, chipping, peeling, and chalking.

On the other hand, to make them safe for indoor use, interior paints contain lower levels of VOCs. And since they aren’t exposed to the external environment, they don’t need mildewcides and other compounds that are usually designed to make paints suited to withstand environmental elements like UV rays and mildew.

Yes, you can mix exterior and interior paints. However, this will only work if you mix paints that contain the same type of base.

For example, you can mix water-based interior paints with water-based exterior paints. You can mix them even if they are of different brands.

However, mixing oil-based paint with water-based paint won’t work. This is even if they are of the same brand.

It is important to keep in mind that interior paints and exterior paints are made up of different chemicals. And even though you can mix them, you may end up with less-than-desirable results.

For example, if you use the mixture indoors, you can still end up compromising your home’s indoor air quality. And in case you use them outside, the resulting mixture won’t be great at withstanding the elements.

It is inadvisable to use an interior primer under exterior paint because these primers aren’t designed to withstand the outside environment.

As a result, when used outside, the primer won’t hold up as well as an exterior primer. This will then lead to paintwork that won’t last as long as it would have had you used an exterior primer.

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Ben McInerney
Author: Ben McInerney - is a qualified arborist with 15 plus years of industry experience in Arboriculture. He ran a successful tree service before turning to writing and publishing. Ben is dedicated to providing users with the most accurate up-to-date information on everything trees.