How Do I Stop Peeling Exterior House Paint?

QUESTION: Help me, Tim! I’m so darned frustrated! The paint on the outside of my home and a shed keeps peeling. Both have wood siding on them.

Every few years I’m out there scraping and starting over. What am I doing wrong? I follow the directions on the label of the paint can to the letter. Is it the paint? Is it something I’m doing wrong? Is it just the weather where I live?

I’m beginning to think an evil hex was cast upon my house by an enemy of a former owner. Please help me because I don’t want to put up vinyl siding to eliminate the paint issue. Debbie S., Waterloo, IA

Do you have chronic peeling paint issues at your home or business? A friend of mine has it here in New Hampshire on some cottages he owns. Peeling paint is a burr under the saddle of many I’m afraid and the causes are numerous. I don’t know that I can cover all of them in the small amount of space provided for this column. Let’s get started.

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Why Doesn't Paint Peel From Cars?

I feel the best way to understand why paint peels is to step back and think about all the things you know of that are painted but you almost never see them peel. How about your car or truck? What about street signs? What about painted aluminum siding, gutters, and downspouts? How about lawnmowers, snowblowers, and many garden tools you might own?

Do you know someone who has a house covered with fiber cement siding? My house has it. There’s not one place where my paint is peeling. My neighbor’s house has the same siding. Both houses are twenty years old, and there’s not a speck of peeling paint in our harsh New Hampshire weather!

The one thing in common with everything above is the paint is applied to things that are not wood. Wood is a very interesting material but it doesn’t play well with most paints unless you paint it correctly before it’s installed.

Why Does Paint Peel From Wood?

Paint peels from wood because wood shrinks and swells. Wood is hygroscopic. This means that water can easily enter wood either as a liquid or a vapor. The issue is when most wood gets wet, it swells and expands in size. Metal and fiber cement siding don’t change shape when they get wet. This is very important.

Now let’s think about paint. What is paint in its most basic form? Paint, for the most part, is just colored glue. The chemistry of most paints is not too far from common white and yellow glue or caulk that you might purchase at a paint store or home center. My original business partner and I used to paint homes in the summer in college. He went on to get a Ph.D. in chemistry where he worked for 30+ years for the largest paint company in the USA. Over the years, he’s taught me much about paint.

What About Lead Paint Danger?

Lead paint danger is real. You can get very sick removing lead paint. Read all about lead paint danger here.

Is Paint Just Colored Glue?

Yes, I realize I’m oversimplifying it, but think about paint. It’s made to stick to things just as glue adheres to things. Paint can have all sorts of other characteristics to minimize color fade, gloss, etc. but when the dust settles, its main job is to stay stuck to the things it covers.

Here’s the rub. If the wood that’s under paint moves too much, that is expands and contracts as it gets wet and dries, this movement can be more than the paint can handle. When the bond breaks between the wood and the paint film, the paint peels.

Will Water Vapor Cause Paint Peeling?

Paint can also be pushed off wood by the vapor pressure under the paint. If wood gets wet and the sun heats up the wood siding, the water in the wood can turn to vapor creating a blister. This vapor pressure can easily pop the paint right off the siding. You can demonstrate this by coating a balloon with a thin coating of flour and water. Let it dry, blow up the balloon and the flour pops off.

Debbie did all she was supposed to by following the paint label instructions. Do you? Do you actually wash the surface you’re going to paint like you wash your car or dishes? You need to rub the surface with soapy water, rinse and allow to dry. Do you scrape off all other loose paint? You wouldn’t put on fresh clothes to go out to dinner after sweating all day working in dirt and grime, right? You’d take a shower. So make sure your surface is squeaky clean.

When is the Best Time of Day to Paint?

Painting at the right time of day can play a part. It’s best to follow the sun. This means to paint in the shade, not in direct sunlight. It’s best if the paint dries slowly. Painting on hot breezy days is perhaps the worst time to paint in my opinion.

Should Wood Trim and Siding be Pre-Painted?

If you want the paint to stick well to wood for many years, you need to shrink wrap it in the paint. This means you need to paint the wood on all sides and edges. You can pre-paint wood siding and trim with primer and finish paint and then install it.

Should Cut Ends of Wood Be Painted?

However, if you cut siding or trim to length, you then need to paint the cut end. Most carpenters are reluctant to do this because it really slows them down and it can be a mess. But the cut end of siding and trim is the place where water enters wood the easiest! These cut ends must be sealed if you want to prevent peeling.

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