Last week we looked at lava rocks imported into this volcanic island. This week we look at lava rock that is not lava at all, nor is it rock. It's a “;duplicate of what Mother Nature can create,”; explained Brian Joy, of Big Rock Manufacturing in Mapunapuna.

Established in 1983, Big Rock's rocks have a 50-year warranty. And why not? They're made of cement and designed to be used outside in whatever nastiness the weather system can throw at it. It lasts like ... rock.

How they're made is a bit of a trade secret, says Joy, but essentially they are a lightweight cement mixture, tinted for a consistent color and poured into molds. Then they're coated with a lithochrome stain, like an acid wash, that becomes an integral part of the rocks and gives it its rocky appearance.

Other people make fake rocks, and you can even buy molds to pour your own paving stones. Big Rock's expertise, however, is “;Hawaiian”; rocks in all their detail, from moss rock to coral blocks to Ulupalakua stones to blue-rock “;plantation”; stones.

Joy, who started the business with Bonnie Cooper and who originally hails from Manchester, England, admits he can't drive down the street without becoming fascinated by the rocks he sees. “;There are so many shades of gray and brown!”; he exclaimed. “;I'm addicted to rock!”;

Why cast rocks? For one thing, that makes them flat on the back, easier to mortar to an existing wall. Despite their heft, cast rock is also about half the weight of real rock. And real rock also must be mined—the sweet spot for gently rounded moss rock from Oahu is buried in Waianae mountainsides—which makes it expensive.

And real rock is also annoyingly shaped by Mother Nature, who likely didn't have your home in mind. An outfit like Big Rock can make the rock to fit your project, instead of the other way around.

Joy has noticed that in this blighted economy, the number of do-it-yourselfers has increased. If a homeowner wants to cover a cinder-block wall with a faux lava-scape, Big Rock provides enough bits to fit it all together like a jigsaw puzzle.

“;And we recommend a mortar mix—we provide the recipe and the dye—to attach the pieces. We don't recommend thin-set adhesive for a veneer. It doesn't hold up like a concrete product. And we tell everyone, look, if you get in trouble, we'll come help you out. In 27 years only one person has done that, and that's quite good,”; said Joy. “;It's a perfect weekend project if you have patience and don't mind getting your hands dirty.”;

Some customers have asked for specific hues to their rocks. Joy doesn't remember anything weird, however. They wouldn't be buying rock in the first place if they didn't want it to look like rock. The general request is to make coral a sandy-beige instead of the bright white it really is.

Best-sellers are generally large steppingstones for Japanese-style gardens, said Joy. It's a natural-looking way of dressing up a garden. Doing a driveway will cost you roughly $8 a square foot, still cheaper than a concrete pour.

Big Rock tries to keep everything in the catalog in stock. If things must be cast on demand, it takes about a week for the mix to harden properly. “;In eight days it's cured 80 percent,”; said Joy.

Another thing to watch out for is water contact. If the faux rock is exposed to chlorinated or salt water, a different formula stain is called for to prevent the surface from eventually changing hue.

Big Rock's expertise is such that Bishop Museum has called upon it to make exact duplicates of ancient Hawaiian pieces, like salt basins and game boulders.

By this point you've probably guessed the company motto. “;Not your average rock group!”; laughed Joy.