Flickr image courtesy of lavenderstreak.

Q: I have a bathroom vanity I no longer use. It has a glass top and two glass shelves. The glass is tempered. The top is 6 millimeters thick and the shelves are slightly less than 5 millimeters thick.

Can I safely use the glass as shelving on my deck? I’ve found stainless steel cable devices with which to hang the shelving from the house wall. The devices will support up to 150 pounds. I’d like to put some plants in pots and some decorative items on the shelves.

A: Your tempered-glass shelving project is totally doable — providing you don’t want to change the size of the glass.

Tempered glass is one of two kinds of safety glass used in places where standard glass could be dangerous. The other type of safety glass is laminated glass. Laminated glass is a sheet of clear plastic sandwiched between two pieces of glass. It’s most commonly used in car windshields.

Tempered glass is manufactured using a thermal process, where ordinary glass is superheated and then cooled. The curing process strengthens the glass and makes it heat resistant. It’s required for use in windows close to the floor, skylights, door windows, shower doors — in short, wherever breaking glass might cause injury.

Tempered glass is four to five times stronger than standard glass. It does not break into sharp shards like ordinary glass. Rather, it shatters into small oval-shaped pebble-like pellets if it fails.

Tempered glass must be cut to size or pressed to shape before the curing process. It cannot be reworked once cured. (It is possible to “uncure” tempered glass, but the process requires special lasers or a 900-degree oven, tools we’re willing to bet you don’t have.

Kevin learned the hard way that tempered glass couldn’t be cut many years ago. He was working on a kitchen with floor-to-ceiling windows. He needed to replace one of the panels with a smaller one, and being a rookie, he decided to cut the panel. He scored the glass with a glasscutter and tried to break it along the line.

When that didn’t work, he placed a broom handle under the line and pressed down with his hands. Nothing. Finally, he stomped on the edge. It broke into a million tiny pieces.

The edges of a typical piece of tempered glass are very weak. This is caused, in part, by the rapid release of heat during the cooling phase of the tempering process. To help compensate for this weaker area, the glass is ground and polished on the edges.

The stainless steel cable system you mention sounds as if it will work just fine. Another option is to screw a couple of 1-by-2 boards, cut to the length of the shelves, into the wall. Leave a groove that’s the thickness of the glass between the wood in which to slide the glass.

Support the outside edge of the shelves by metal cables clamped to the edge of the glass and anchored into the walls with stout hooks.

Make sure the shelves are level, both side to side and front to back. Also, be sure the cable hangers are solidly attached to the house as well as the glass. Spread the load over as much of the surface as you can. Use several smaller plants and knickknacks rather than placing one large container in the center.

A final word of warning: Be very careful not to give the edge of the glass a serious rap. If you do, you’ll be sweeping up thousands of little glass pebbles.