Can you use exterior paint inside?

Paints are divided into two types based on their end-use: exterior paints and interior paints. People who are into home decoration and remodeling may wonder if they can use exterior paint inside the house. This thought can cross their mind due to multiple reasons. Either they want to recycle old paint lying around the house or they could be tired of the paint job getting spoiled now and then.

The urge to make use of old paint and being tired of constant repainting can lead you to speculate if you can use exterior paint inside. However, before taking this decision you have to check whether it’s in your best interest and well-being to do it or not. As you might’ve already guessed there’s a stark difference between both types of paint and how they perform.

What are these differences? What is exterior house paint and what is interior paint? What are the advantages and disadvantages of using exterior paint indoors? Most importantly, is it safe?

We will discuss all of these questions below. But first, let’s understand the difference between interior and exterior paint.

Difference between interior and exterior paint

Exterior house paint is used in painting exterior walls, buildings, and areas prone to sunlight, wind, and other outdoor conditions, whereas, interior paint is used to paint the inside: living spaces, bathrooms, and furniture that are not susceptible to exterior elements.

If we examine the chemistry; there are four major differences between the two paint types:

1. Paint composition
2. Type of solvent used
3. Odor quality
4. Quality of finish

Paints consist of four primary ingredients; solvent, resin, additives, and pigments. The solvent is a medium that carries the additives, resins, and pigments. It transfers the paint to the surface and evaporates off at room temperature.

The pigment imparts color, while additives give specific characteristics to the paint, such as UV resistance, protection against mildewcides, premature breakdown, etc. Once the paint dries off, the resin adheres the pigment and additives to the surface.

Paint composition

Interior and exterior paints usually have similar solvents and pigments. Some pigments fade away quickly so, they are not used in exterior paint. The main difference between the two is the addition of different resins and additives.

In contrast to interior paints, exterior paints have to withstand extreme weather fluctuations – from heavy winds to salty breezes. The resins used in exterior paint are flexible compared to interior paint – which is rigid. The flexible resins expand and contract with the surface when subjected to different conditions. Thus, they keep the paint intact.

Additives improve the overall performance of the paint by providing specific properties like water resistance, UV blocking, fire resistance, etc. They are mainly added to exterior paint to compensate for the effect of harsh weather. By incorporating these additives in the recipe, the exterior paint can survive for an extended period.

Interior paints have to perform inside the house; thus, they are made of resins that can sustain indoor traffic, bumps, and scrapes on the painted surface. Special additives are added to interior paint to minimize splatter and give a smooth application.

Interior paints are manufactured from organic pigments, which give brighter and vibrant shades. Their organic nature makes them less durable and susceptible to the outdoor environment. However, they can withstand light scrubbing and cleaning.

Type of solvent

Generally, water-based paints are used to paint the interior, and oil-based paints are used to paint exterior surfaces. Latex paint, which is water-based paint is also used for outdoor painting jobs.

Oil-based paints contain a high level of VOCs and mineral oil as a solvent. The purpose of these compounds is to carry complex additives and resins. They aid in transferring the paint from the can to the surface. Water-based paints contain water as a solvent and little to no VOCs.

After the application of exterior paints, the VOCs evaporate into the air leaving behind pigments and resins as freshly coated paint on the surface. However, during this evaporation toxic fumes are emitted into the environment that harms health. These fumes are more evident in enclosed spaces.

Quality of odor

Exterior paints have a strong odor that lingers on for some time. The smell is produced by the high quantity of acrylics, VOCs, and additives like fungicides. Proper ventilation is essential to wave off the smell and its harmful effect on an individual’s health.

If exterior paint is used indoors, the particles remain dispersed in the air and irritate the eyes and skin. That is why interior paints are manufactured to give as little smell as possible, that can vanish after a while.

Quality of finish

Interior finishes have many options to choose from, whereas exterior finishes comprise a narrower range. Interior finishes include matte, eggshell, gloss, semi-gloss finish, etc. This makes it convenient for interior decorators as they can choose a suitable finish depending on the requirement of the surface.

E.g., flat finishes hide imperfections but are harder to clean. Low luster finishes give a shiny appearance. and gloss finishes give a tough and durable coating. They are mostly used to paint window sills, ceilings, and doorcases.

The resins and additives present in the exterior paint allow it to withstand extreme weather. However, these heavy-duty additives make the coating thick and less attractive.

An interior latex paint that lacks weatherproofing additives cannot be used to paint outer walls as it wouldn’t last long. Similarly, a bathroom or a kitchen cannot be painted with exterior latex paint because of an unattractive finished surface.

Using exterior paints indoor

People are drawn towards using exterior paints in their homes because they provide an edge over interior paints. However, the disadvantages outweigh the benefits they offer. Before painting indoors with exterior paint, compare the advantages and disadvantages to make an informed decision.

Advantages

1. Exterior house paints are preferred for painting bathrooms. This reason because some bathrooms don’t have a proper ventilation system. Hence, moisture builds inside and causes mildew. Painting the bathroom with exterior paints – which contain additives like fungicide and mildewcides – prevents organism growth. Thus, the paint lasts for a long time without the need for repainting.
2. Interior house paints wear off after a year or two. This is because they are not manufactured to be as durable as outdoor house paints. Using exterior paints in the garage or kitchen; areas exposed to heat and environment can make them last for as long as 10 years.
3. Exterior paints consist of inorganic pigments which give higher covering capacity owing to their large particle size. They can easily hide imperfections of a wall and

Disadvantages

1. One of the biggest drawbacks of using exterior house paint indoors is the toxic fumes that cause health problems. The fumes are released as VOCs evaporate during curing. As a result, dizziness and breathing issues become common in the spaces painted with exterior paint.
2. Interior paints are formulated while keeping indoor complications in mind. Exterior paints on the other hand are prone to scuffing and scratches – which is a common indoor problem. They are also hard to clean. Walls painted with interior paint can be easily cleaned by scrubbing.
3. Exterior paints have limited options to choose from in case of finishes, whereas interior paints have as many as six choices of finishes available. Interior paints also have an easier application process compared to exterior paints.
4. The odor of exterior paint sometimes becomes unbearable. Proper ventilation through windows and exhaust fans is required to minimize this issue.

The most serious risk factor in using outdoor house paint is fumes

Paint fumes are volatile compounds that evaporate after the application of exterior paint. Due to their toxicity, these fumes pose a serious risk to human and animal health.

Exterior paints tend to outgas high levels of VOCs when they evaporate. The outgassing can go on for several months to years, which aggravates health issues like headaches, nausea, respiratory disorders, and even damage the central nervous system.

According to Environmental Protection Agency (EPA), the concentration of VOC is about 10 times higher indoors than it is outdoors. This exposes the people to inhale dangerous pollutants which remain suspended in the air for a long time.

Research explains that these chemicals get absorbed in an individual’s blood through inhalation or skin contact and penetrate the organs. These fumes are potentially toxic for young children, pregnant women, and the elderly. Maternal exposure to paint fumes induces the risk of lower birth weight which is related to delayed development and learning disabilities

Hence, exterior paints are used to paint buildings and areas where the effect is minimal and less apparent. In contrast, interior paints emit little to no toxic fumes and also cure relatively faster than outdoor paints.

Interior paints are best suited for painting living spaces. However, if you still want to try painting the walls of your house with exterior paint you will have to keep certain precautions in check to lessen the harmful effects it brings forth.

Tips on how to use exterior paints inside

If you have already painted your walls with exterior paints or thinking about painting them, take the following measures to be least affected by its consequences.

1. The area to be painted with exterior paint should have a proper ventilation system. Multiple windows, doors, and fans should be present to aerate paint fumes. This process should be carried out for a while since exterior paint tends to outgas even after curing.
2. Always use exterior paints with the minimum level of VOCs if you want to protect your lungs. Latex water-based paints have low VOC than many oil-based paints. Consult with an expert on the toxin level beforehand.
3. Some plants absorb a low level of toxins. If you have painted a room with low VOC exterior paint, place these plants over there to absorb the pollutants and freshen up the air.
4. Install a VOC air purifier if the air becomes too unbearable to breathe in. These filters are a good investment to clear the air of toxins and protect your health, albeit being a bit expensive. However, nothing is more precious than your life.
5. Stay away from the room freshly painted with exterior paint for as long as possible. Most importantly keep the kids, elderly, and sick away until the paint cures.

FAQ

• Can I use exterior latex paint inside?

Exterior latex paint is made up of heavy additives and resin that give the paint a thicker consistency and an unattractive finish. Interior painting requires a precise and clean finish that cannot be achieved by using exterior latex paint.

The exterior latex paint also contains high levels of VOCs compared to interior latex paint which is harmful to health.

• Can I mix interior and exterior paint?

Mixing different types of paint means compromising on their individual properties. If you mix interior paint with exterior paint and use it to paint outer walls, the durability will be visibly reduced.

Similarly using it inside means that the paint will crack and start flaking; because the paint will not collude as interior paint is not as flexible as exterior paint

• Can I use exterior paint in my bathroom?

No, it is not recommended to use exterior paint in bathrooms because the paint contains fungicides and mildewcides. These additives are not approved by EPA for indoor living capacity.

If your interior paint gets ruined by moisture buildup, consider installing an exhaust fan. It makes a difference. Also priming the wall with mold prevention primer and painting it with mold prevention paint afterward also resists biotic growth (assuming that the previous mold has been killed before applying the primer and paint).

• Should I use interior or exterior paint in my garage?

If your garage is an open area, you can use latex paint with low VOCs. However, just to be on the safe side, experts recommend using interior paints since a garage also comes under interior living capacity.

• Can I use interior paint outside?

Interior house paint can be used outside, e.g., to paint a fence or an old brick wall, but you should be aware that they do not last long. Interior paints are not resistant to sunlight and other natural conditions thus they deteriorate on exposure.

If you apply interior paint on the exterior surface, be prepared to repaint it more often.

So, can you use exterior paint inside?

Paints are formulated keeping in mind the requirements of their intended use. Although it may seem otherwise, interior paint should be the foremost choice for painting indoors. Using exterior paint inside comes with a plethora of cons. Although they have certain advantages over interior paints like durability etc., their adverse effect on health cannot be disregarded.

These effects are, however, not as visible outdoors. In short, it is best and safe to use interior paint indoors and exterior paint outdoors.