I painted the outside of the house, and it faded in a couple of months. I also observed there were some places where the paint was chipped. The paint I used was fresh and nowhere close to expiry. However, upon researching and found out that I used the wrong type of paint outside. Different kinds of paints vary in properties. That is when I discovered that labeling the paint cans as interior and exterior paint is not a business strategy but an actual paint classification.
Different kinds of paints are synthesized to cater to different needs. Interior paints are adapted to stain resistance and ease of regular cleaning. Interior paints are different from exterior paints mainly due to their chemical makeup. On the other hand, exterior paints are designed to withstand weather changes.
Can I use interior and exterior paints interchangeably? Will it save me cost or become a spilled glass of wine on a white dress? Let’s take a deep look at how the two types of paint vary as I answer all questions you may have in mind.
Compositional difference between Interior and Exterior Paints
The four main paint components are binders, pigments, additives, and bases. Variations in these lead to the differences in properties of Interior and Exterior paints.
Binders or Resins
Resins are commonly known as binders. They are the substances that hold the paint pigments with the base and make the paint adhere to the wall.
Exterior paints are manufactured using soft resins, which can expand or contract based on weather conditions. The flexibility in exterior paints is essential to prevent cracking during the winter season.
However, the resins used in making interior paints are inflexible and rigid. Since interior paints are not exposed to such drastic temperature changes throughout the day, the resins used here do not possess flexibility.
Exterior paints use acrylic binders, whereas silicon or epoxy binders are found in interior paints.
Modern paints incorporate various additives in the paint formula to enhance the outlook and improve the efficiency of paint. Additives can be any additional element added to the paint that is not part of the general paint formula and the dye or pigment.
Interior paints contain leveling agents, antimicrobials, glitters, and conditioners as additives.
Some examples of additives found in exterior paints are UV blockers and thickening agents to improve the functionality of the paint.
Pigments are substances that give the paint its color.
The nature of pigments in interior paints is purely organic. Due to the smaller size of organic pigments, we notice a much smoother blend in interior paints. Moreover, they are taken from plants and animal extract, thus safe to be used inside.
Exterior paints incorporate pigments derived from earthly minerals. Due to their larger size, these inorganic pigments provide a highly durable finish to the exterior walls.
The base is the solvent used to dissolve the resins, additives, and pigments. It is the key component that gives the paint its texture and allows mixing all the components to create a blend that can be applied to the walls.
There are two main kinds of bases; water base and oil base.
Most interior paints are water-based, which allows easy cleaning and stain resistance inside the house. They also dry out more quickly than oil bases.
Exterior paints are oil-based. Oil-based paints provide water and temperature resistance; however, they take much longer to dry.
Learn more details about the composition of interior paint in our blogs.
Differences in Paint Properties
Due to the differences in composition of the paints, you can notice a difference in their properties as well. These can be measured as differences in weatherproofing abilities, durability, VOC levels etc.
On the exterior of your house, you experience stress, such as twigs falling off the trees, footballs hitting the walls, often kids running into it with their skateboards, and years of climatic distress. This demands higher durability, which is precisely how exterior paints are manufactured.
Even though interior paints can withstand a specific amount of stress, they are not as tough and durable as exterior paints.
Adhesion is the ability of the paint to stick to the wall surface. Interior paints require adequate priming before painting as they display excellent adherence to the primer.
You can learn about this in detail by reading our blog on the primer requirement before painting your interior.
However, exterior paints adhere strongly to walls without primer as well. Most exterior paints will also adhere to brick or wooden surfaces; however, there will be differences in finishing when you’re not using a primer. Read more on this topic and learn whether you need a primer for your exterior walls.
Exterior paints have various additives to keep the paint weatherproof, temperature, moisture, and UV resistant. While exterior paints dry out, they release toxins that one must not inhale. Usually, the wind carries them away, which is not an issue while painting the exteriors.
Since interior paints have lesser additives added to the formula, they do not outgas harmful fumes.
Interior paints are stain resistant to keep up with the aesthetics of a clean house. Nonetheless, there can still be tough stains on the walls, perhaps your kid’s doodles. This may require heavy scrubbing, peeling off that area’s interior paint.
Exterior paints are more rigid and can resist scuffing and scrubbing better without affecting the paint.
Exterior paints have high VOCs compared to interior paints. These are harmful to health, and despite being highly durable, VOC emission is the main reason exterior paints cannot be used indoors.
An average house experiences sunlight for almost 12 hours a day. The rays shine bright, hitting your house at least 6 hours daily. That is a lot of saturated energy coming in contact with your house. Exterior paints incorporate additives that can withstand such strong beams of light and contain intense pigments that don’t fade away under the sun.
The interior temperature of the house hardly fluctuates. Thus temperature resistance is not a characteristic we find in interior paints.
Exterior paints encounter harsh temperatures, fluctuating throughout the day; thus, additional additives are added to exterior paints that make the paint temperature resistant and prevent cracking. The temperature-resistant additives are absent in interior paints, making interior paints unfit to be used on the exterior.
Exterior paints contain moisture-resistant additives to protect your house against severely fluctuating humidity, rainfall, hail, and melting snow.
Interior paints hardly undergo washing once or twice a year; therefore, moisture resistance component is absent in interior paints.
Since the interior undergoes cleaning and disinfection regularly, molds and mildew do not build up on interior paints. Additional mildew protection is not required in the formula. Moreover, mildew preventive chemicals fume out for years and thus are unsafe to be used in interior paints.
On the other hand, mildew is a severe risk on the exterior, and thus exterior paints contain mildew-prevention additives.
The sun carries heat, light, and harmful radiation, known as UV radiation. UV radiations can bleach out pigments in your paint, causing it to fade and appear dull. Since the outer walls are exposed to the sun directly, exterior paints require UV protection.
Interior paints do not require UV protection additives as sunlight doesn’t hit the inside walls directly.
Every time you purchase an exterior paint bucket, you’ll see a sticker that says weatherproof. Because it is the exterior that faces rain, snow, hail, dust storm, falling leaves, and harsh sunlight, they contain weatherproofing. The exterior secures the interior; thus, it does not require weatherproofing. This is why interior paints are not weatherproof.
Exterior colors are in contrast to the surroundings. The most common exterior colors are gray, white, blue, autumn red, dull yellow, etc. thus, most exterior paints revolve around these shades. Interior color schemes differ as people choose colors like olive green, pastel pink, lavender, and teal, so you will find interior paints revolving around these shades.
You can also learn more about interior paint colors and how they affect temperature.
The cost of interior and exterior paints is quite similar; however, the difference still exists. Interior paints are more on the affordable side, whereas exterior paints tend to be a bit expensive due to the additional additives added to them.
If you want to know the amount of interior paint you need for your house, you can go through this detailed blog.
Similarities Between Interior And Exterior Paints
Interior paints and exterior paints are both used to paint your house. They are both made up of four essential components; resin, also known as binders, additives, color pigments, and a water- or oil-based base.
Both these paints are available in various finishes such as matte, gloss, semi-gloss, mild shine, satin, etc., with a vast range of colors to choose from. Whether you’re painting indoors or outdoors, you need paint maintenance every 5 – 7 years.
Are interior and exterior paints interchangeable?
Since the basic makeup of interior and exterior paint is quite similar, the two most obvious questions arise. Can I use interior paint outside? Or can exterior paint be used inside? After all, they are just paints.
No, interior and exterior paints are not interchangeable. Interior paints must strictly be used inside the house, whereas exterior paints should be used on the outer walls. Not only will their efficiency as a paint be affected when used alternatively, but they can also cause serious health hazards.
For example, interior paints outside will decrease the paint’s lifespan, as interior paints aren’t weather, temperature, or UV resistant. They will fade away faster when exposed to the sun, calling for a yearly touch-up.
Similarly, when exterior paints are used inside the house, they outgas harmful fumes that irritate the eyes, throat, and nose. Headaches, nausea, and fatigue have also been reported after exposure to the volatile compounds in exterior paints.
To avoid surpassing your yearly home maintenance budget, ensure a healthy environment, and guarantee the longevity of paint, interior and exterior paints must not be interchanged.
Frequently Asked Questions
Is exterior paint thicker than interior paint?
Exterior paint is thicker than interior paint as exterior paints contain rigid binders and additives, increasing the paint’s density. Since exterior paint is supposed to withstand harsh conditions, it requires a thicker coat supported by the thick formula of exterior paints.
Should exterior and interior colors match?
There is no defined rule on whether exterior and interior colors should match. Your exterior color is chosen in contrast to the surroundings, whereas your interior color is chosen following the furniture. However, having similar tones will allow a smoother transition from the house’s exterior to the interior setting.
Can you DIY exterior paint?
Of course, you can! DIY painting is trending all over the world. People are taking up the responsibility to paint their own house with their families, which also leads to quality family time. However, painting requires time, patience, and expert advice to enhance your skill set and achieve a professional finish.
Can I mix interior and exterior paint?
If both the interior and exterior paints are water-based or oil-based, they can be mixed. However, water doesn’t dissolve in oil. If the bases used in the paints are different, they should not be mixed.
Moreover, exterior paints have higher VOCs than interior paints. If paints are chemically compatible for mixing, you must be careful of the ratio while mixing both the paints.
Summing it up
Exterior and interior paints are not merely labeled on a paint can but are actual representations of the product. Interior paints differ significantly from exterior paints based on their chemical nature and usage. Exterior paints are designed to bear the harsh UV radiation and combat wear and tear due to weather changes. On the other hand, interior paint is meant to give a smooth and aesthetic finish and resist stains. They must not be used interchangeably for optimal finish, durability, and longevity.