Can You Use Exterior Paint Inside? – Interior vs. Exterior Paint

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Whenever you want to repaint your house inside and outside, you always try to save money wherever you can. Maybe you have used some exterior paint on a section of your house outside and you still have almost a full tin leftover, and you have a few things to paint inside. So, can you use exterior paint inside? Read further to discover the answer and more.

Interior vs. Exterior Paints

It is very important to first understand the difference between exterior and interior paints before we can answer the questions like can exterior paints be used inside or can interior paints be used outside? Although both types of paint appear to be very similar, each one has its specific use. The primary difference between exterior as well as interior paints is in the composition, particularly the resin used during manufacturing.

Paints are made up of components like solvents, pigments, resins, and additives. The solvent in latex paints is water, while the solvent for oil-based paints is usually mineral spirits. The solvent causes the wet state of the paint and as it dries the solvent evaporates, leaving behind the resin, pigments, and additives that remain in the paint. The pigment provides the paint color, and the resin makes sure the paint adheres to the surface. The resins can also be made using acrylic, epoxy, or silicone. The additives give the paint its properties like resistance to mildew or growth, making the paint easy to apply as well as easy to clean up afterward. In both the interior and exterior paints, the solvents and pigments are much alike.

The choice of resin is what sets interior and exterior paints apart. The resin is what is used to bind the pigment to the surface, so with exterior paints, the important thing to consider is the weather, moisture, and temperature variations. Exterior paints also need to be resistant to sunlight, chipping, peeling, and fading. So, the resins used in exterior paints make them more flexible to be able to deal with temperature changes.

Interior paint does not have to be flexible to contend with weather, temperature, or fading from the sunlight. The resin used in this type of paint must instead be more rigid, making it able to resist scuffing, cutting, staining, smearing, and easier to clean.  

Interior Paints

Different paints all have different properties, and their formulation reveals the purpose for that type of paint. This is the reason why interior paints are specially designed to resist staining, fading, and yellowing. The paint should hold up to knocks from vacuum cleaners, furniture, kids, and pets every day. Therefore, interior paints are formulated with additives and resins that give them a smooth finish, which enables them to hold up to scrubbing, dusting, washing, and cleaning daily.

One other main characteristic of interior paints is that they produce a lot less odor since they have fewer VOCs (Volatile Organic Compounds). This is a very important aspect of interior paints, as you do not want strong odors indoors, which can cause severe health issues. Interior paints, unlike exterior paints, do not have any weather-proofing additives as they do not need this type of protection.  

Exterior Paints

In the early days, exterior paints were all oil-based as this property was able to give a durable and strong finish. However, today technology has advanced so that exterior paints are mostly water-based, and the acrylic resins help to do what the oil did in the early days.

Exterior paints contain more additives, which enable the paint to resist harsh outdoor elements. This means that the exterior paints have to be able to resist rain, wind, moisture, and even snow. The paint also needs to endure temperature variations and still maintain its color, even after many years in the sun. 

Exterior paints contain more flexible and softer resins that aid in resisting mildew, chipping, and peeling. The flexibility of the paint means it can contract and expand with temperature changes. These paints are also highly water-resistant. Exterior paints also contain a great deal more toxic chemicals called VOCs (Volatile Organic Compounds), which include mildewcides, fungicides, and UV blockers, which is one good reason not to use exterior paints indoors. Let us condense all of these factors into a table for interior vs. exterior paint.

Can You Use Exterior Paint Inside?

Can exterior paint be used inside? Technically you can use exterior paint indoors, but there are many valid reasons why you should not, as there are many more acceptable options available. Exterior paints contain resins and additives that help the paint resist mildew, staining, and fading from the sun’s rays. They can also stand up against any adverse weather conditions like rain, snow, and varying temperatures.

Due to the durability of exterior paints, it may seem that these paints should hold up indoors as well. Especially in the bathroom, where you can reduce the mold and mildew on the walls. However, there are some risks attached and certain reasons why you should not use exterior paint on your inside walls.

Exterior paints, including acrylic latex paint, are formulated with a much higher percentage of VOCs and release strong toxic odors that are potential health risks to people who have allergies and breathing problems. Even when the paint has cured, it can still emit those harmful odors, which may prove to be dangerous in confined spaces, causing headaches, nausea, and lightheadedness.

All the resins and additives that are contained in exterior paints are essential to make the paints resilient to outdoor conditions and can age and cure outside having no effect on the quality of air inside your home. Apart from the durability of exterior paints, they are still prone to scratching and scuffing when you apply them indoors. Since exterior paints have solvents in their formulation, they are a lot more flammable than interior paints. So, you should avoid potential risks and dangers and use paint inside that is safe and keeps your family healthy.

So, can you use exterior paint inside? Yes, you can, but only if it is in an outside shed, garage, or building where nobody sleeps. Also, make sure when you have to go into those outside buildings, you ensure all the windows are open and there is a good cross-flow of air. 

Can You Use Interior Paint Outside?

Using the interior paint outside can be done and is not in any way hazardous to you or your family’s health. However, even though you can, there are quite a few reasons why you should not use interior paints on outside walls.

• Interior paints do not contain resins and additives that make exterior paints durable, so they will not stand up to the elements.
• Interior paints are not formulated to contract and expand with temperature variations, so they will be prone to form hairline cracks.
• Interior paints are not designed to face direct sunlight, so they will fade very quickly.
• Since interior paints are thinner in consistency, they require more coats, which is an added expense.
• Because interior paints are not designed for outdoor use, they will take longer to dry outside.

What if You Accidentally Used Exterior Paint Inside?

What must you do if you discover that you accidentally used exterior paint inside? The very first thing you must do is open all the windows, especially when the paint is still wet, as this will help with the fumes that the exterior paint emits. This is vital as the fumes that are emitted from the paint can be hazardous to you and your family’s health. You need to stay out of that room until the paint dries, which could be a few weeks or under cold conditions a few months.

You must remove most of the old exterior paint by scraping or sanding. Then you can wash the surface down and allow it to dry. Once that is done, you can apply a stain-blocking primer on the wall, which will put a barrier between the old exterior paint and the new interior paint, this will eliminate all the fumes that remain from the exterior paint.

After the primer has dried properly, you can apply the interior paint. The best-recommended type to use is a semi-gloss as it will make cleaning the walls a lot easier. However, you can paint with a satin or flat finish, but it becomes more difficult to scrub the walls clean at a later date.   

What if You Use Interior Paint Outside?

What must you do if you discover that you accidentally used interior paint on an outside wall? First, there is no need to panic, but you need to understand the paint will not be able to withstand the harsh elements and will start to crack, peel and fade. There are three options you can try.

Remove the Interior Paint and Repaint Using Exterior Paint

This can be challenging; however, it is the best option if you want a good and lasting job done. To remove paint that has been freshly applied is not easy, and you will probably have to use some paint stripper and a lot of hard elbow grease. Then you must prepare the surface, you can do this by first sanding and painting over a primer. Finally, you can go ahead and apply the correct outdoor paint to the surface.

Leaving the Old Paint On

If you do not have the time or are not prepared to make the effort of removing the old paint, you can just leave it alone and let nature take its course. This will mean that the paint will start to crack and peel off. However, the problem is you do not know how long this will take; depending on the quality of the paint and how you applied it, this could happen within weeks or take a few years.

When your painted surface starts to deteriorate, you will have no other option but to remove the old interior paint, prepare the surface by sanding and scraping and then apply a primer. Lastly, apply the correct outdoor paint to the surface.

Paint Over the Interior Paint

The last option available is to simply paint over the interior paint using your exterior paint, which may sound like the best option, but you need to consider some things before you attempt this. You need to ensure that the exterior paint you are going to apply is compatible with the interior paint you have already applied to the surface, as some paints do not react well with others. This will result in your new coat of paint not sticking well to the surface. You may also experience the interior paint beginning to break down over time, and if the base coat of paint starts to show signs of mildew or breaking down, then the top layer of paint will just follow suit and begin to chip.

This option of applying the exterior paint over the interior paint is a temporary fix rather than a proper repair job. You must first understand what will happen before you make your decision. One thing is for sure, you will be careful to never make this same mistake again.

Can You Mix Interior and Exterior Paints?

You can mix exterior with interior paints as long as they both have the same base, which means that you can mix oil-based exterior paint with oil-based interior paint, or a water-based exterior with an oil-based interior. If you are mixing the paints to use inside, then you must ensure you use more interior than exterior paint, to keep your family safe from dangerous fumes.

Similarly, when you are mixing the paints for use outdoors, then you need to use more of the exterior paint than the interior paint, which will ensure you get the best results possible. If you mix more interior paint with less exterior paint for outdoor use, you may discover that the paint will not adhere to the surface properly and will fade quickly and start to crack.

Whenever you are mixing different kinds of paint you should use a primer before you apply the paint. However, we do recommend that when painting outside, you use only exterior paint and when painting inside you use only interior paint to avoid any problems.

Can You Mix Paints That Have a Different Finish?

When you want to mix paints that have a different finish, you must understand a little about paint. For example, what kind of paint are you using? Let us have a look at what different types of finishes there are and what they can do.

Matte and Eggshell Finishes

Matte finish paints have no shine or gloss, so they allow you to hide any imperfections in your walls or ceilings. So, it is not a good idea to use this type of paint finish in your kitchen or bathroom, where you have high humidity, which can ruin your paint finish. This type of paint finish is very similar to that of the matte finish paints, but they are slightly glossier when comparing them to the matte finish. The same applies to this paint as with the matte finish.

Satin Finish Paints

The satin finish paints remind you of satin bed sheets with a luxurious shine, which is what the satin finish paint will give you. This type of paint finish is ideal for use where there is a high-traffic flow, like in a children’s room or the hallway or passage area.

Semi-Gloss and High-Gloss Finishes

The semi-gloss finish paints give you a lovely shiny and very durable finish, which is suitable for use in areas like the laundry, kitchen, or bathroom areas. The high-gloss finish paints are similar to the paints used by the artist, and with the proper preparation, you will be able to turn the walls in your house into a mirror effect. This particular finish is better suited for furniture.

Now that we understand a bit more about the type of finish in the paint and what it can do, is it possible to mix the different finishes? When mixing paints with different finishes, like semi-gloss with satin, all that it does is lower the shine of the semi-gloss paint. The same applies when mixing matte and eggshell or eggshell and satin. However, it is not advisable to mix the extremes like a high-gloss with a matte finish, as you will not end up with a good result.

Can You Mix Paints of Different Brands?

Nothing is stopping you from mixing paints from different brands, but you need to understand that different brand paints are manufactured using different formulas. This includes the pigments, solvents, binders, and additives as well as color mixtures. When you mix these different brands, they may not mix very well as each brand is unique and no paint brand is the same. So, it is always best to use a single brand when painting.

Can exterior paint be used inside? This has been our main discussion and we have discovered that each type of paint is designed for a specific purpose. Exterior paint is specially designed to withstand the harsh weather conditions outside, while interior paints are designed for indoor environments. Ultimately, the best option is to keep the exterior paints for outdoor use and interior paints for indoor use.

Frequently Asked Questions 

Are There Differences Between Exterior and Interior Paint?

Exterior paints are specially designed to combat mildew, mold, chipping, fading, and cracking. On the other hand, interior paints are specially designed to be stain-resistant and are easy to clean. Interior paints are also more environmentally friendly than exterior paint.

Can You Apply Interior Paint Over Exterior Paint?

Technically, it is possible, but you will find great difficulty in getting the interior paint to bind properly unless you first apply a primer and then apply the interior paint. However, if the paint is to go outside then you will need paint that can withstand the elements.

Can You Use Interior Paint for Your Front Door?

You can paint your front door with interior paint but only on the inside, if you want to paint the outside you need to ensure that the door is protected, otherwise the paint will start to chip, crack, fade and peel off.

Can You Use Water-Based Exterior Paint Inside?

Even though it is water-based, it is still exterior paint and is, therefore, not suitable for interior surfaces. The finish is softer and more flexible, and it also emits toxic fumes, even after it cures. So, other options are recommended.