For those of us working in the real world, where almost nothing is level or plumb, shims frequently come to the rescue. While tapered shims – often taken from a bundle of cedar shingles – are useful, they don’t offer much compressive strength, and, for many jobs, I need shims that won’t crush under a load and that have a consistent thickness. On exterior jobs, of course, the shims also need to be waterproof and rot-resistant.
One alternative to conventional shims that has come in handy in my work is scraps of vinyl flooring. Home centers are a great place to pick up material samples, which usually measure about 3 inches square and vary in thickness from 1/16 inch to over 1/4 inch thick.
Every once in a while, though, I need something thicker and capable of carrying some load. That's when I break out the high-density polyethylene (HDPE) box of scraps I keep in my truck. This material is tough, with a compressive strength of 4,600 psi and a melting point of 260 degrees F (according to gplastics.com), and is water- and rot-proof. HDPE is easy to cut; it doesn't split when you're driving fasteners through it; and it comes in many colors and thicknesses. Shim-sized pieces of HDPE are available as scraps from many sign maker’s shops, or can be purchased from a plastics retailer; in a pinch, you can buy an HDPE kitchen cutting board and run it through the saw for the size you need.
Need convincing? About 10 years ago, I made standoffs from ½-inch-thick HDPE shims for the 4x4 posts supporting the roof over my backyard patio. The posts are still in perfect shape, and so are the shims.
