Converting a gas grill to cook using lava rocks involves simply adding lava rocks below the grilling surface while ensuring they do not touch the gas burner elements. The grill must have a grate over the burners that is strong enough to hold the lava rocks and is no wider than needed to prevent the rocks from falling through.
Some manufacturers pre-install lava rock grates over the gas burner elements, and others offer lava rock grates as optional add-on parts. If a manufacturer grate is not available, steel mesh, also known as expanded steel, serves well as a lava rock grate. Steel wire mesh is another option, as long as the wire is thick enough to support the lava rocks. Wider grill openings require thicker material. The grate must hold the rocks at least one inch above the burners to avoid interfering with the combustion of the gas.
Once the protective grate is in place, pour in a bag of lava rocks, which is available at most hardware and landscaping supply stores. Arrange the lava rocks close together in a single layer, leaving enough room for some heat from the flame to pass between the rocks. The lava rocks absorb heat from the gas flame and distribute it evenly across a broader surface to improve flavor and heating efficiency. Smoke from drippings that fall on the lava rock provides characteristic barbecue flavor and aroma.