Remove and sort any loose bricks. Clean bricks with a stiff-bristled, but not metal, brush. The powdery white coating might be residue from salts that rise to the surface. It can be removed by scrubbing. Allow bricks to dry before applying mortar because water encourages more residue. Discard crumbling bricks.
Replace missing and discarded bricks with matching kiln-fired bricks. Find old bricks in good condition at salvage yards or demolition sites
Reset the missing bricks. Kaile Warren, of CBS’s Early Show, suggests mixing mortar to the creamy consistency of soft serve ice cream. Drop mortar along rows of brick and make a V-shaped trough to set bricks in. Slather the ends of bricks with more mortar. Wiggle bricks down into the mortar until they are level with the old bricks. Strike the new mortar with a tuckpointing tool or mason’s trowel to match the old mortar.
Clean out old mortar that has fractured with a caulk remover, paint scraper or narrow metal brush. Brush out the dust and spray the crevice with water. Squeeze new mortar into the spaces and strike to match the old mortar. Scrape away excess mortar.
Set three-eighths to half inch bolts or pieces of reinforcement bar into loose mortar to hold the grates. If the barbecue does not have grate supports to use as models, insert two supports halfway up the inside barbecue wall and two from 12 to 16 inches higher. Do this on both sides of the cavity.
Remove mortar drips with your trowel or brush. Allow them to dry slightly before scraping to avoid leaving cement smears.