So, you have been painting your house and find yourself at an impasse – you realize you don’t have enough paint to finish the master bedroom. Then, a brilliant idea pops into your head. You have a half-gallon of the same color paint, but it’s exterior paint, so you ask yourself: Can I mix interior and exterior house paint?
The answer is yes; you could mix interior and exterior paints. However, the exterior paint has a much higher amount of VOCs in its mixture, which could harm you when used indoors.
While it is possible to use exterior paint indoors, you need to be mindful of where and how you apply it. In the sections below, I’ll share what you need to know about mixing interior and exterior paint.
Let’s dive into the details.
What are the Differences Between Interior and Exterior Paint?
In the past, if you wanted your paint to be resistant to mildew, you needed to buy exterior paint. Thankfully, most interior and exterior paints now contain a degree of mildewcide – this is why your bathroom doesn’t grow mold or mildew all over the walls.
Mildewcide concerns people when mixing paints, but Federal regulations keep this additive well under potentially harmful amounts.
What is problematic about using a mix of exterior and interior paint inside the house is a VOC (Volatile Organic Compounds) component. The solvents are responsible for keeping paint in its liquid solution until application. Unfortunately, VOCs can cause serious health effects in both the short and long term.
The regulations for this paint component are different between interior and exterior paint. In most cases, the exterior paint has a much higher concentration of VOCs in its mixture than interior paint.
These solvents off-gas fumes that are particularly problematic for the respiratory system. While you can get away using exterior paint inside a room or hallway, it will smell to high heaven, give you a headache, and potentially damage the lungs.
So if you must use exterior paint or a homemade mix of interior or exterior paint inside, keep it well ventilated, with fans and open windows.
While latex paints will dry within a few hours, it can take up to a whole month for exterior paint to fully cure. Unfortunately, this means it will be off-gassing harmful fumes the entire time it’s curing.
If you have anyone in your household with respiratory issues or children, be aware that this can potentially harm them.
Can you Mix Paints with Different Finishes?
When mixing two different paints, be very mindful of the type of paint you’re using. Since there are many different types of paint, take some time to get to know your paint.
You have, in order from least reflective to most reflective:
- Matte Paints: These paints have almost no shine to them, allowing them to hide dimples and imperfections in walls and ceilings effectively. However, avoid using this type of paint in the bathroom or kitchen, where high humidity and splattering can ruin the finish.
- Eggshell Paints: Similar to matte paints, eggshell has just a tidge more shine to them, also perfect for the same uses.
- Satin Paints: Think satin sheets. Imagine that luxurious shine because that’s how this paint will finish. This paint is more suitable for higher-traffic areas of the house, such as hallways or children’s rooms.
- Semi-Gloss Paints: Shiny and durable, semi-gloss paints are suitable for places like the bathroom, laundry room, and kitchen.
- High-Gloss Paints: Think the high-arts of the paint world. With solid prepping, you can turn the walls of your bathroom mirror black with the right high-gloss paint. Perfect for accent and furniture work.
Okay, so now you know whether you can mix your paints and come out with something similar to the original color and finish. You can mix two paints with different finishes, but it will dull the reflectiveness and shine.
For instance, you can mix a semi-gloss and satin paint and notice a small drop in the shine of the mixed product. Depending on what you are using the paint for, this may not be a problem. The same goes for mixing eggshell and matte or satin and eggshell.
Mixing the extremes like a matte and a high-gloss will not have great results; it’s just best to save those paints for smaller projects.
Can you Mix Water and Oil-Based Paint?
Another thing to consider before mixing paints is what type of base.
Generally, there are two types of paints:
- Oil-Based paints are the traditional long-lasting paints that stand up to years of abuse before needing repainting. However, they off-gas much longer than water-based paints and take longer to dry.
- Water-Based paints or latex paints are more modern, quick-drying, and less prone to show brush strokes and overlapping when fully cured.
You don’t want to mix these two types of bases regardless of the color or finish. Water and oil don’t like to mix.
Can you Mix Different Brands of Paint?
You should always feel encouraged to try new things and make happy little mistakes. Sometimes the best way to learn is to give something a try and see how it goes.
Yes, you can mix different brands of paint.
But, you should know that paints are comprised of 4 different components:
- Pigments – which are the crushed minerals that give the paint its color.
- Solvents – the chemicals responsible for keeping paint in a solution.
- Additives – the component of paint that controls dry time and contains the mildewcide mentioned earlier.
- Binders – the part of the paint that helps form a layer.
Different brands have different recipes for their colorful concoctions. When trying to mix two different paint brands, beware that even if the paints seem similar, they may not mix. Why? Each brand can have a unique process to create its paint.
However, you may be pleasantly surprised and find that two different brands go together like peanut butter and jelly.
My advice: if two different paint brands are just setting around with no use, go ahead and try to mix them. See what happens. It might be great.
Note: Exterior paints generally have more acrylic pigment. The differing chemical compositions make it hard to paint over exterior paint with interior paint. While you can mix the two, trying to layer them will often come with unseemly results.
Is Exterior Paint More Durable than Interior?
Yes, exterior paint is generally considered more durable than interior paint.
People design exterior paint to withstand wind, rain, snow, ice, and hurricanes. However, it’s important to understand what we mean when we say durable.
When comparing interior and exterior paint, think about interior paint like glass and exterior paint like rubber.
Let me explain.
Interior paint has a higher degree of hardness than exterior paint. Hardness helps prevent the paint from scuffing. It also allows people to clean their paint easily.
On the other hand, exterior paint is not as hard as interior paint, but it is more durable.
In the next section, we’ll go over an example.
Interior and Exterior Paint Hardness vs. Durability
Would you want to drive a car with glass tires? No. The glass tires would crack and eventually shatter. However, if you try to stab a window with a knife, it’s very difficult to break the glass. Why is this? Because the glass has a low degree of durability but a high degree of hardness.
Most would rather drive a vehicle with rubber tires; however, you can easily pierce the tire with a sharp knife.
What’s the point? There is a difference between durability and hardness.
Hopefully, this analogy helps you understand the difference between interior and exterior paint.
Exterior paint is not as hard as interior paint. Exterior paint can bend and move as the temperature changes. However, if you use exterior paint indoors, it may be more prone to scratches – just like the rubber tire is more prone to stabs than a glass window.
Likewise, if you used indoor paint outside, it is much more likely to chip and crack under the changing forces of nature. We discuss this more in the next section.
Can I Use Interior Paint Outside?
Interior paint is not as durable as exterior paint. If you try to use interior paint outside, several things will happen.
First, your paint is more likely to fade. The sun is brutal on interior paint. For this reason, if you want outdoor paint to stay true to color, it’s a good idea to use exterior paint.
Second, interior paint is not as flexible or durable as exterior paint. We explained this principle in-depth in the last section. Exterior paint does not dry as hard as interior paint. It helps to imagine exterior paint as being more like rubber while interior paint is more like glass.
However, if you just have a touch-up project on an old fence, or you want to use up some indoor paint before winter, there’s no problem with placing some indoor paint in an inconspicuous outdoor area.
Just know that indoor paint won’t last as long as exterior paint when it is used outside. Also, using indoor paint outside could create a hassle in the future when you need to repaint, as the flaky indoor paint won’t provide a good surface for a new coat.