What is the Difference Between Interior and Exterior Paint?
Leftover paint. Every home has some. It takes up valuable space in the garage or storage shed. It can’t be poured down the drain and (in some areas) it costs to properly dispose of it. So, what to do with it? Is it okay to just use it on whatever needs painting?
Don’t Use the Wrong Specific Paint Types for Different Paint Projects
Not all paint is created equally. If the chemical formulation for interior and exterior paint products was the same, all paint would be labeled alike and the designation of interior and exterior wouldn’t exist. Understanding paint applications and paint types is key but most people don’t have the benefit of having worked in the paint industry to understand these differences.
Why Using Exterior Paint Indoors Won’t Work
Using paint for an indoor project that was intended for exterior use will cause several problems. Defining what the paint was originally intended for will bring these important differences to light.
Exterior paint requires:
- the ability to resist intense changes in temperature
- the ability to withstand heavy rain or wind damage from dirt, sand or debris
- the ability to repel insects and fungus
As exterior paint is formulated for those elements, it’s not designed for:
- splatter resistance
- washability and stain resistance
- high hiding and good flow for touch ups
To illustrate these differences, here’s a scenario. The leftover white paint from the deck isn’t appropriate for the wooden table and chairs in the kids’ playroom. Both surfaces are wood but the similarities end there. The furniture will be difficult to keep clean as the exterior paint does not contain any washability or stain resistance. Not possessing splatter resistance, it will be messier to use.
Worst of all, because of the fungicides present in exterior paints, any loose or flaking paint can and likely will cause illness in young children if ingested. Interior paints are formulated to be mercury/lead free by law and do not require fungicides in their formulations.
Why Using Interior Paint Outdoors Won’t Work
Just as exterior paints are formulated for their intended environment and exposures, so are interior paint products.
As stated, some of these properties include:
- good washability
- quicker drying times
- lower odor
Using interior paints outside produces several issues as they are not designed for:
- ultraviolet light resistance for color retention
- resistance to the elements
- severe changes in temperatures
- insect infestation
An example of this reverse situation would be leftover paint from the kitchen being used on something like a picnic table. Regular sunlight will cause the color to fade. Because the table is continuously exposed to changes in temperature, these paint types won’t have the flexibility to adapt and will easily crack. If the temperatures aren’t drastic enough to cause trouble, the first hard rain will and will cause the paint to lift and peel.
Any open wood will suffer from rot as there won’t be any moisture barrier to protect it. Interior paint doesn’t contain fungicides to repel insects so the exposed wood will be open to termites, ants, wood beetles or bud worms.
What is Being Painted is as Important as Where it is Being Painted
Virtually all paints and coatings are designed for a specific purpose. True, there are obvious differences between high and poor quality paint but even the most expensive kitchen and bath paint will fail if used for painting aluminum siding. Exterior painting or interior painting techniques start with making the right paint choices.
Read the labels, ask questions of the local paint store expert and make an informed decision on the correct paint applications for any paint waiting to be used. And, if still concerned about that leftover paint in the over-crowded garage or storage shed, the paint store can likely offer a practical, cost-effective and legal solution for that, too.