I had some paint left over after painting my living room walls. Awakening the artist inside of me, I decided to give the front wall of my house a new look.It turned out excellent and I was so glad that my paint didn’t go wasted. However, what happened a few weeks later was disappointing.
You cannot use interior paint outside because of the difference in chemical compositions of both paints. Interior paint cannot bear the exterior environmental effect. Even though interior paint does not cause any damage to the exterior walls, it will fade away and chip off faster. You will have to repaint your walls soon, adding to the overall painting cost.
The color started fading and the paint started chipping off. I had to repaint my front wall. If you also want to save time, effort, and money, you must know how interior paints are different from exterior paints, so you do not end up making the same mistake as myself.
Difference Between Interior and Exterior Paint
They have different names for a reason. Interior paints are different from exterior paints mainly because of their chemical composition. Even though all kinds of paints are made up of binders, additives, and pigments in a base, each component has different properties for different purposes.
1. Binders
Paint binders or resins are chemicals that hold the pigment together to create a durable film. The paint’s adhesion, durability, and stain resistance depend on the binder type. Paints contain different kinds of binders depending on their use.
Exterior paints use acrylic as the binding resin. Acrylic binders are soft and ideal for outdoor environments. These resins can expand or contract in different temperatures while maintaining their form. They also prevent the paint from cracking and peeling off under sunlight or heavy rainfall.
On the other hand, interior paints contain thick, rigid resins. They are neither flexible nor able to withstand the harsh outdoor environment but can hold up against regular cleaning and scratches. Interior paints use silicone or epoxy binders, unlike acrylic ones, which do not have a harsh odor.
2. Additives
Modern paints contain additives to enhance the paint’s appearance and function. Additives are added in the form of thickeners, emulsifiers, leveling agents, and antimicrobials. Additives used in interior and exterior paints vary because they serve different purposes.
Interior paint additives include levelers, conditioners, glitters, and scents since they are used for decorative purposes. They give extra gloss and shine to your interior to make it look fresh and smooth. Interior paints do not contain harmful chemicals, making them safe to use indoors.
Exterior paints, on the other hand, have numerous additives in them. They contain antimicrobials, UV blockers, and many VOCs (Volatile Organic Compounds) that help the paint toughen and protect against harsh climatic conditions.
3. Pigments
The finely ground particles that provide paint its color are the pigments. Paint pigments are of two types; organic and inorganic. Organic pigments are transparent and derived from animals or plants, while inorganic pigments are obtained from mineral rocks. The durability of the paint depends on the type of pigment used.
Exterior paints contain inorganic pigments. Since they are based on metallic compounds, their particle size is big and provides high coverage. Inorganic pigments are resistant to UV lightening and temperature changes, making them suitable for outdoor usage. They are more durable and long-lasting than organic pigments.
Interior paints have organic pigments because the house’s interior is not exposed to direct sunlight. Organic pigments are not UV light resistant and offer much less covering capacity. Due to their small particle size, they blend easily into the solvent and give off a cleaner look when applied.
4. Bases
The base is an essential component of paint. It is the solvent into which all other ingredients are mixed and applied. It evaporates after some time, leaving the binders, additives, and pigments attached to the surface. Regarding bases, there are two kinds of paints; water-based and oil-based.
- Water Based Paints
Water-based paints, also known as latex paints, use water as their solvent. All the pigments, resins, and additives are dissolved in a water solution. This kind of paint is used for interior painting because it is easier to clean and scrub. If you’re wondering, “can I use interior latex paint outside” you probably can.
The water molecules evaporate at room temperature and are not adapted to direct sunlight, so it is better to keep them for indoor use only. Water-based paints do not give off any harsh odors and are suitable to be used indoors.
- Oil Based Paints
In oil-based paints, mineral spirit or turpentine is used as the solvent. Oil-based paints make the pigments appear brighter and smoother than water-based paints but take longer to dry. They also have a strong smell and require sunlight to be cured.
Oil-based paints provide a thicker and harder coat but are challenging to clean. They can resist moisture and sunlight and last longer than their water-based counterparts.
| Interior Paint | Exterior Paint |
| Contains silicon or epoxy binders | Contains acrylic binders |
| Less or no VOCs. UV blockers and antimicrobials are absent. | VOCs, UV blockers, and antimicrobials are present. |
| Bleaches out under direct sunlight | Can withstand direct sunlight |
| Pigments are organic | Inorganic pigments are used |
| Water-based paints | Oil-based paints |
| Bearable odor | Unpleasant odor |
What happens if you accidentally use interior paint outside?
Using interior paint outside is a common mistake many people make. However, this does not cause any damage. The only drawback you will face is that your paint will chip off faster. This is because interior paints do not contain additives used in exterior paints to make them last longer.
The Interior paint is thin and does not adhere well on outdoor surfaces. It cannot withstand the harsh outdoor environment; as a result, cracks appear faster, and the paint peels off quicker.
If you have accidentally used interior paint outside, you can seal it by applying a coat of exterior paint sealer. This will provide some resistance, and the paint will not come off too soon.
Using interior paint over exterior paint
If you had your house painted by a professional before you decided to take up this job, you are most likely to have exterior paint outside.
Technically it is possible to use interior paint over exterior paint. Still, it is essential to remember that different kinds of paints vary significantly in formulas and should not be used interchangeably.
Interior paint does not adhere well to exterior surfaces or paints. It is recommended not to use interior paint over exterior paint because it will peel off quickly. However, if you have no alternative, you can use a primer. Priming the surface will help the paint bond properly and make the paint last some time.
Remember that interior paint cannot withstand temperature changes, UV radiations, mildew, or humidity. And despite using a primer, the paint will not last very long.
Hybrid or Universal Paints
A particular type of paint, commonly known as hybrid or universal paint, bridges the two kinds of paints; interior and exterior. These have been designed specifically for people who wish to give their houses a fresh look without professional help.
Hybrid paints are a unique combination of oil and water-based paints that provide excellent adhesion and durability on indoor and outdoor surfaces.
While these paints are suitable to be used on the interior and exterior of your house, they do not provide heavy-duty resistance on the exterior. Hybrid paints lack the additives necessary to protect against mildew, moisture, and temperature fluctuations. They are ideal for use indoors and in small outdoor projects like doors, window frames, and even garages.
Hybrid paints last longer than usual interior paints but are not as tough as actual exterior paints.
FAQs
Can you mix interior and exterior paint?
Interior paints and exterior paints should not be mixed. Combining the two shortens the paint’s lifespan, affects its consistency and makes application difficult.
In addition to that, the mixed interior and exterior paint cannot be used indoors due to the high amount of VOCs present in exterior paint. And when it is used outdoors, it increases the chances of mildew and paints peeling faster.
Is exterior paint thicker than interior paint?
Yes, exterior paints are thicker than interior paints. This is because most exterior paints are oil-based. Oil-based paints are thicker than their latex or water-based counterparts, which is why they appear thicker in consistency.
Another reason is the addition of heavy-duty additives and binders. These are added to exterior paints to provide resistance against extreme weather changes and prevent it from cracking or peeling off.
Is exterior paint more expensive than interior paint?
Exterior paints are comparatively more expensive than interior paints. This is because exterior paints have additional chemicals and compounds that make them resistant to the outdoor environment. They are formulated to last longer and provide extra protection from moisture, mildew, and UV radiation.
In contrast, interior paints are more basic in their formula and are cheaper than exterior paints.
How long will the interior paint last outside?
Interior paint is not designed to withstand the outdoor environment and does not have the adhesive qualities of exterior paint. Using interior paint outside does not last long and starts to crack and peel off very soon.
Depending on the weather conditions, interior paint lasts only about a year or two maximum when used outside.
Using interior paints outside – Know the consequences
If you think of using the leftover interior paint outside like I did, you might have second thoughts. Interior paints differ significantly from exterior paints. They cannot survive the rough conditions the exterior walls are exposed to and fade away rapidly. There are paints specialized for the exterior walls; you should use them if you wish to paint outside.
I also realized that I painted the house wall at the wrong time of the year, if you do not want to do the same mistake then check out our post which tell you details about the best time of the year to paint.