Can I Use Interior Paint on Exterior Surfaces? (& Why Not)

Interior paint is designed to provide a protective layer to walls and other indoor surfaces. Exterior paint is designed to protect and enhance outdoor surfaces like walls, fences, and siding. While it may be tempting to use interior paint on exterior surfaces, you should understand the differences between the two and why it is not recommended.

Common issues if you use interior paint on exterior surfaces are the paint is not weather resistant, it will appear patchy, and it is not heat or sun-resistant. Common issues if you use external paint on interior surfaces are the paint can be easily scuffed, hard to clean, and have harmful fumes.

Using the right paint in your home is important so that your walls look great and last long. Paint can keep out water, resist the sun, and help your home’s resale value. You should try to always use exterior paint outside and interior paint inside. Let’s get into why this is so important.

Key Differences Between Interior and Exterior Paint

In terms of their physical properties, exterior paint is usually thicker and more durable than interior paint. It is also designed to be more resistant to moisture, UV rays, and other harsh weather conditions. In terms of color, exterior paint is almost always made with a higher pigment level. This way it can provide a more vibrant and long-lasting color. 

Exterior Paint

When it comes to application, exterior paint needs to be applied in multiple coats. The exterior paint will need a primer coat and two or more finish coats. Unlike interior paint usually only needs one or two coats.

Exterior paint has to be applied around a temperature of 50 degrees Fahrenheit or higher. Interior paint can be applied at a much lower temperature. The cost of exterior paint is also usually higher than interior paint. This is because it is designed to withstand more wear and tear over time. 

Interior PaintExterior Paint
Thinner and less durableThicker and more durable
Pigment Level LowHigh Number of Coats
Lower CostApplication Temperature Lower temperature 50°F

Water-Based Paint

Water-based paint is a type of paint made with water as the base. It is also made with synthetic resins and acrylic. It can come in a variety of sheens and finishes. 

Water-Based Paint

Water-based paint is usually a better interior paint because it is easier for you to apply, dries quickly, and is less likely to emit VOCs. It is also easier for you to clean and is more environmentally friendly than oil-based paints. 

Oil-Based Paint 

Oil-based paint is a type of paint made with oil as the main ingredient. It is typically made with alkyd resin and mineral spirits and can come in a variety of sheens and finishes

Oil-Based Paint 

Oil-based paint is usually better for the outdoors because it is more durable and offers better protection against moisture and UV damage. It also has better adhesion than water-based paint and can be used on a variety of surfaces.

What Happens If I Use Interior Paints on an External Surface?

Using interior paints on an external surface can cause a variety of issues. The paint may not adhere to the surface properly, leading to peeling and chipping. It may not be able to stand up to the elements, leading to fading, cracking, and discoloration. The paint may also not be designed to resist mildew, mold, or other environmental factors, leading to more rapid deterioration.

Not Weather Resistant

Interior paint is not weather resistant, which can be a big problem. When exposed to the elements, such as rain, snow, or extreme heat, the paint will wear away more quickly than if it were made for outdoor use. This can create a need for more frequent repainting. This can be inconvenient and costly for you. 

The paint can be more easily damaged by scratches, fading, and other signs of wear. This can detract from the appearance of the house, and make it look older and less well-maintained. 

In the long run, this can cause higher maintenance costs for you and a shorter life for the paint job. Without proper protection, the paint will not last as long and will need to be replaced more often. 

This can make it difficult to keep the exterior of the house looking nice and can be a burden on the homeowner. The paint may not be able to withstand changing weather conditions. Which will cause more damage.

Appear Patchy 

When interior paint appears patchy, it is usually due to improper application or poor surface preparation prior to painting. If you apply a new layer of paint over a dirty, wax-covered, or glossy surface can prevent the paint from adhering properly, resulting in a patchy finish. Paint that is applied too thickly may also dry unevenly, leaving behind a patchy appearance

To fix a patchy paint job, you should try to find the problem at hand. If the surface was not properly prepared, it should be cleaned and sanded before any new paint is applied. 

If the paint was applied too thickly, you should wipe it off with a damp cloth. Then let the area dry before you add any new paint. If you used the wrong type of paint, you should try to remove it and the area should be primed before applying a new layer of paint. 

Once you have prepared the wall for new paint then a new layer of paint can be applied.

Not Heat or Sun Resistant

Interior paint that is not heat or sun resistant will wear easily. It will begin to fade, crack, and blister as it is exposed to the intense heat and light of the sun. The paint will become brittle and start to peel and flake off. This will make your paint job look unattractive. 

This is a problem because the paint will need to be replaced more frequently. You’ll have to put in additional time, effort, and money on repairs. The fading of the paint can cause an overall loss of aesthetic appeal in a room or home. This can reduce the value of the property.

If the fading of the paint is severe, it can lead to structural damage to the interior of the home. This can be costly and time-consuming to repair. It may also reduce the life expectancy of the building.

What Happens if I Use External Paints Inside?

Using external paint on interior walls can have serious consequences. The paint can contain chemicals and toxins that are not suitable for indoor use. Meaning it could be dangerous for people and pets living in the home. These toxins can contaminate the air, leading to respiratory problems, skin irritation, and even long-term health problems. The paint also may not adhere properly to the walls, resulting in peeling and cracking. This can lead to expensive repairs.

Easily Scuffed

External paints can easily scuff due to various factors. The most common cause is abrasion. This happens when something rubs against the painted surface and causes the paint to wear away. This can be caused by things such as wind-blown debris, dirt, and sand. 

Acidic substances such as sap, bird droppings, and certain types of cleaners can cause the paint to soften and scuff. 

Exposure to sunlight can cause the paint to break down and become more susceptible to scuffing. All of these factors can contribute to the paint becoming easily scuffed, leading to a need for regular maintenance and touch-ups.

Hard To Clean

External paints can be difficult to clean due to the longevity and durability of the paint. The paint is designed to last for many years, so it has a high resistance to scrubbing and cleaning materials. 

The paint is also applied in multiple layers and can be a combination of different materials. This means it can be difficult to remove all of the paint without damaging the underlying surface. 

You should use a soft cloth and gentle detergent to clean external paint. Try to avoid using abrasive materials or harsh chemicals. For tougher stains, a pressure washer may be used, but it should be used with caution as it can cause damage to the surface. 

You should wash the area multiple times with mild detergent and warm water to ensure a thorough clean. After each wash, the area should be dried with a soft cloth to remove any remaining residue.

Harmful Fumes

External paints can emit a variety of harmful fumes, such as volatile organic compounds (VOCs). VOCs are released into the atmosphere as the paint dries and can cause a number of health problems, including respiratory irritation, headaches, nausea, and dizziness. 

Long-term exposure to VOCs has been linked to more serious issues such as cancer and liver damage. External paints emit hazardous air pollutants. These pollutants can cause irritation to the eyes, nose, and throat, as well as an increase in asthma attacks and other respiratory issues. 

The dangers of external paint fumes can be severe for children, the elderly, and those with existing health conditions. You should take all safety precautions when painting, such as using a respirator, opening windows, limiting exposure time, and wearing protective clothing.

Conclusion

Overall, you should not use interior paint on exterior surfaces. Exterior paint is specifically designed to withstand harsh weather conditions and is formulated with certain ingredients that interior paint does not have Exterior paint is typically thicker and more durable than interior paint, making it more suitable for outdoor surfaces.

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