Plastic wood. Sounds like an oxymoron. But recently a homeowner asked me to replace rotting entrance door kickboards with a material that looks like wood but won't soak up moisture. And it had to hold paint. Forever.

What it is

My search led me to the world of synthetic wood -- products made from plastic. I'm not a chemist, so I can't begin to explain the chemical properties of these products. But most start with plastic and tweak it to produce workable densities. A critical component is a UV inhibitor, which manufacturers claim is added to reduce yellowing.

One process uses a hot-water shower as the extrusion is formed, which hardens the board. The more common process lets the extrusion cool as it rolls down the manufacturing line, the result being a softer finish. Products made using the first process are less vulnerable to hammer marks than those made by the second process. Remodelers should evaluate each product's performance to determine which will work best for them.

Using the product

In general, when cutting these products, all tools should be carbide tipped. Still, be careful of residue build-up on the tool from heat. Ring- or spiral-shanked galvanized or stainless steel nails are needed, and the nail must be held flush with the surface. Some manufacturers recommend nailing from the middle out, not from the ends in. Because the material typically expands and contracts in length, you must leave a gap between boards when fastening, or, with some of these products, you can use 45-degree or 22-degree cuts. Always check with the manufacturer for spacing recommendations. Recommended spacing can be as much as 1/4 inch. Use 100% acrylic caulk; avoid silicone-based caulks, because they do not adhere well to these products.

If you like white, you'll like the factory finish coat common to these products. If you're thinking of dark colors, they'll absorb heat and cause expansion, although Precision Composites' Royal Wood uses an acrylic cap that is heat resistant, allowing for darker colors. Check with the manufacturer to learn if special primers are needed.

Product choices

I learned of three particular products through research for my customer, as well as through article research for the Journal of Light Construction: Royal Wood from Precision Composites, SynBoard, and AZEK Trimboards. The three are attractive products to me because they have the weight and feel of wood.

Royal Wood sports an acrylic exterior wrapped around a core of wood fiber and ABS (Acrylonitrile Butadiene Styrene) plastic. It's available in several patterns, including a reversible tongue and groove with a V-groove on the back. There's also a one-piece outside cornerboard.

SynBoard is a solid PVC product and comes with a 10-year warranty. The manufacturer claims it can come in direct contact with the ground and can be bonded to itself with PVC adhesives. SynBoard is extruded by the hot shower process (meaning fewer hammer dings), and it also comes with a factory-applied latex primer to help prevent yellowing. SynBoard is based in Texas, but your local lumberyard's sales rep should know how to get the product from the distributor.

Bill Posey, owner of W.E. Posey in Shelburne, Vt., reports good results with AZEK Trimboards. He's been using them for two years. They have the same weight and density as wood. He says their uniform composition and high UV resistance allows him to install trim with no additional painting -- except around the main entrance, where he fills nail holes and applies fresh paint. AZEK recently added AZEK Cornerboards to the existing product line, which includes AZEK Beadboard and AZEK Sheet.

An accountant by education, Posey pays close attention to the bottom line. While AZEK is more expensive than wood, the lack of waste -- AZEK comes in 18- and 20-foot knot-free lengths -- and the fact that it's pre-painted makes it a break-even decision. Reduced water absorption of synthetic wood also means fewer callbacks because of product failure, especially in high-moisture areas.

So now, you have two choices: real wood or plastic. --Lee McGinley, CR, a Big 50 remodeler, has written for the Journal of Light Construction. He lives in Addison, Vt.