For DIYers desiring a loftlike setting, a drab floor slab can be jazzed up with an acid-stain treatment. The acid reacts to the concrete, etching patterns and variations on its surface. You'll see it used most often on flooring in restaurants such as the Yard House in Waikiki or in trendy boutiques.

“;With stains in general, you can't control every aspect of it. It's kind of its own living beast,”; said Morgan Conger, an independent contractor. “;So what you'll end up with oftentimes is abstract art on a concrete canvas.”;

Jeff Rapozo, branch manager of Bonded Materials Co. on Puuhale Road, said although the word “;acid”; scares people, “;it's not as potent as muriatic acid used in swimming pools.”; You do need to wear gloves and protective eyewear, Rapozo cautions. “;It will stain your fingertips.”;

He describes the procedure as fairly simple, used by homeowners as much as contractors as an option to painting floors for a more natural look. “;The acid stain is probably one of the most popular products we sell here for the do-it-yourselfer.”;

As far as cost, it's comparable to painting a floor.

“;The acid stain, unlike paint, etches its way into the concrete, and (coupled with the sealer) it's more durable than paint,”; which is why it's popular for commercial spaces.

The stain is sold in gallon containers at Bonded, enough to cover about 200 square feet. “;Your typical home-improvement store would carry acid stain, however because Bonded is a supplier to contractors, the brand we carry, L.M. Scofield, is a commercial grade and more potent,”; Rapozo said.

It's sprayed onto the bare surface, taking 15 to 20 minutes to react - or as long as two hours. Acid left on the surface is rinsed off and neutralized with a mixture of baking soda and water. After that, Rapozo said, most customers put on a sealer, which enhances the color and protects the floor.

Often, it's the prep work that takes the most effort - tearing out existing tile, then grinding the surface to prepare it for the stain.

If the concrete is marred or gouged, microcoating might be in order, said Pat Erwin, an independent mason. He just completed such a procedure - in which cement with fine silica is applied, sometimes in triplicate, and then sanded - on the gazebo pads that surround the Royal Hawaiian Hotel's pool. “;It makes the floor look brand new,”; before it absorbs the stain, said Erwin.

“;It's a good idea for do-it-yourselfers to get some coaching beforehand, either from the folks at Bonded or other experts, because although it's easy to do, it can also be easy to mess up.”;

Otherwise, he said, try an instructional video by floor artist Gaye Goodman of Faux Real Floors (www. acidstainconcrete.com), which has step-by-step instructions.

Aside from a being a simple flooring option, it's also environmentally sound, said Conger. Other coverings such as carpets eventually need to be replaced, and that material just adds to landfills. Using the bare slab - treating it with stain or grinding it down and polishing it - “;you're actually building 'green,'”; said Conger.

“;I just saw a friend in Texas who ripped off all the tile and carpet in his house and stained the pre-existing slab. It had different stress marks, and cracks, but that just adds to the character of the house.”;