Tools & Materials
Which Wood Substitute Works Best?
Doing some exterior work on a house and trying to decide which material to use? Here’s a quick guide on why you probably shouldn’t use wood, as well as a look at some of the alternative materials you can use instead.
Make the Switch, Ditch Wood
When it comes to building a house’s exterior, it turns out that a lot of things are better than wood. Wood is a troublesome material for exterior work. It shrinks and swells, rots, warps and feeds insects. Years ago, builders used wood because that was their only option. But today, you have better choices. So ditch the real wood—and all the headaches—and go for something that looks just as good!
Why Wood Isn’t Worth the Worry
Wood trim expands and contracts with changes in humidity. Paint can flex with that movement for a while. But eventually, tiny cracks develop. Those cracks let in moisture, which causes more movement, which leads to larger cracks and peeling, rot … you get the idea.
One of the big advantages of manufactured products is that they remain stable when exposed to moisture. That means the paint lasts longer. Like all materials, they move with temperature changes, but that movement is less extreme and easier on the paint than moisture movement. A related advantage of manufactured products is that they don’t warp or split like wood so you don’t have to hunt for straight, good-looking boards
So What Are the Alternatives?
We soaked five types of trim in a bucket of water for about a month. That’s not a scientific simulation of real-world conditions, and most of these products aren’t intended for that kind of punishment. Still, we think the results are worth sharing:
Cellular PVC and poly ash: These two materials were completely unaffected—just what you’d expect from products rated for ground contact.
Fiber cement: This seemed unaffected by the water, which surprised us because it’s not approved for ground contact.
Composite and Engineered Wood: Both swelled near the edges but didn’t blister or blow apart.
Next we’ll go into a little more detail on what makes some of these wood alternatives unique.
Because it’s plastic, cellular PVC trim will probably last longer than the rest of your house. It’s rot-and-insect-proof and doesn’t absorb water, which makes it a great option for trim that’ll get wet a lot. It’s also the most expensive—about twice as much as other manufactured options.
Cellular PVC looks and cuts just like wood and comes in traditional widths and thicknesses. You can work it with regular power tools, blades and router bits. It expands quite a bit along its length when it’s hot out or the sun hits it, so it’s important to fasten it well with nails or screws, being sure to drive them through the sheathing and into framing members. You’ll need to leave 1/8 in. of space for heat expansion per 18 ft. of trim (skip this if it’s already hot outside).
This kind of trim looks like medium-density fiberboard (MDF), but it’s made to handle weather extremes. It’s basically wood fibers mixed with resins with chemicals added for insect and rot resistance. You can cut and rout it just like wood. It comes primed and holds paint very well.
Typically used as a flooring material, engineered wood can also be used as a trim or siding alternative that looks much like oriented strand board (OSB) on the back side but has far better weather resistance. It’s basically compressed wood fibers and resins with a textured shell, giving it the appearance of solid wood. It comes primed, and the boards stay nice and straight during and after installation. It’s treated for rot and termite resistance.
This is a masonry-like product containing mostly cement, cellulose fibers and sand. Unlike wood, it resists cracking, splitting, rotting and swelling. It doesn’t expand and contract a lot, so paint jobs can last for decades. You can’t rout it, however, and dust collection is highly recommended when cutting it. You can cut it with regular carbide blades, but they’ll dull quickly because fiber cement is very abrasive. Use blades made for fiber cement instead. Hot-dipped galvanized or stainless steel nails are recommended and must be set flush. Field-cut edges must be painted. You can get fiber cement trim primed or pre-finished in many colors.
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