Q: The paint on the outside of my home and shed keeps peeling off, and I’m so darned frustrated! Both structures have wood siding. Every few years, I’m out there scraping and starting over. 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 in Iowa where I live? Please help me, because I don’t want to put up vinyl siding to eliminate the paint issue.
A: Peeling paint is a burr under the saddle of many homeowners, I’m afraid, and the causes are numerous.
The best way to understand why paint peels is to think about all of the things you have that do hold their paint without peeling. How about your car or truck, or your aluminum siding, gutters and downspouts? Even lawn mowers, snowblowers and other outdoor tools fall into that category. So does the outside of my 20-year-old house, which has fiber cement siding.
What do these items have in common? They’re not made of wood.
Unfortunately, wood doesn’t play well with most paints — unless, that is, you paint the wood correctly before it’s installed. More on that in a moment; first, some background.
Wood is hygroscopic, which means that water can enter easily, either as liquid or vapor. When most wood gets wet, it swells and expands in size, which can be a problem if it’s been painted.
Paint, for the most part, is just colored glue. Its chemical makeup is not too different from the common glue or caulk sold at a paint store or home center. Paint can have all sorts of other characteristics to minimize color fade, gloss and so forth, 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 beneath the paint moves too much — that is, it expands and contracts as it gets wet and dries — it can be more than the paint can handle. When the bond breaks between the wood and the paint film, the paint peels.
Paint can also be pushed off wood by vapor pressure that forms under the paint. If your house gets wet and the sun heats up the wood siding, the water in the wood can turn to vapor, creating a blister. The vapor pressure can easily pop the paint right off the siding.
To avoid peeling, it’s important to follow the instructions on the paint can’s label. Be sure to scrape off all of the loose paint that you can. Then wash the surface you’re going to paint with soapy water, rinse it off and allow it to dry.
If you want your paint to stick well to wood for many years, you basically need to shrink-wrap it in the paint. By that, I mean you should paint all sides and edges of the wood. You can cover wood siding and trim with primer and finish paint, and then install it.
In addition, if you cut your siding or trim to length, remember to paint the cut end. Some carpenters are reluctant to do this because it slows them down and it can be messy, but the cut end of siding and trim is the place where water enters wood the easiest. The cut end must be sealed if you want to prevent peeling.
Tim Carter has worked as a home-improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.