Lava rock is frequently used in fireplaces because of its aesthetic value and because the rock is fire resistant and will not require frequent replacement. The rock can help keep a fire contained and also retains heat to make it easier for the wood to stay burning. Because of the amount of small lava rock that normally fills the fireplace, the fireplace can take some time to clean. However, cleaning a lava rock fireplace is not difficult.
Remove the lava rock from your fireplace when the fireplace is cool and place it in either a bucket or a plastic bag. Use rubber gloves to help prevent soot build-up on your hands.
Remove any other loose articles from the fireplace and any fireplace tools and take them outside to scrub soot off of them with a scrub brush.
Scoop into a plastic bag any soot build-up from the bottom of the fireplace with a fireplace shovel.
Sweep any excess dust or ash debris out of the fireplace with a small broom and dustpan. You can also use an ash-vac if you have one, but a regular vacuum is not recommended.
Lay down newspaper so the bottom of the fireplace and the first few inches of the walls are covered. Scrub at the inside walls of the fireplace into the chimney with a wire brush. The newspaper will collect the dirt and soot that is scraped off.
Mix 6 tablespoons of trisodium phosphate with a cup of bleach in a gallon bucket of warm water. Wear rubber gloves, safety goggles and old clothes because the solution is corrosive. Place the bucket in the fireplace on top of fresh newspaper.
Dip your wire brush into the solution and scrub the inside of the fireplace until the fireplace is clean.
Scrub each piece of lava rock quickly with a scrub brush over newspaper to knock off soot and debris as you place the lava rock back into the fireplace after the cleaning supplies have been removed. You can also place the lava rocks in a grill, cover them in aluminium foil and turn the heat on high until smoke stops coming out of the grill. This will burn off debris from the rock.