Before I tell you how to clean soot stains from your brick, you need to know that you should never see soot if the fireplace is drafting properly. Soot outside of the fireplace indicates a dangerous situation that needs to be addressed!
Soot is CARBON; when you see carbon it means that associated fume - CARBON MONOXIDE - has been in your living space. A properly drafting chimney will take all soot and fumes up the chimney.
There are 2 basic reasons most fireplaces don't draft properly:
* A fireplace opening that's too large for the chimney
* Negative pressure in the house
FIREPLACE OPENING IS TOO LARGE
The area of the chimney needs to be at least 10% of the fireplace opening size. If the fireplace opening (height x width) is more than 10 times the area of the chimney (length x width) then it's likely to smoke and spill fumes back into the room. Since it's not possible to make the chimney larger, the only option is to reduce the fireplace opening size. This can be done with a smoke guard or by installing glass doors. The frame on the glass doors overlaps the opening on all sides to reduce the opening.
Any device in your home that removes air - dryers, smoke hoods, bathroom fans, central vacs, etc. - MUST get that air from somewhere. They pull air into the house via cracks around doors and windows and, too often, down the chimney. This can create a real problem when trying to burn the fireplace as these appliances can pull smoke and fumes down the chimney.
Negative pressure is a greater problem in newer, more air-tight homes. Since a fire requires air to burn, think of it as another device in your home that needs fresh air to operate so it can also pull air DOWN the chimney at the same time the chimney is trying to VENT SMOKE UPWARDS.
Try turning off other appliances while you're burning your fireplace. If this isn't sufficient to cure the problem then crack the window that's closest to your fireplace so it can provide air to your fire.
If all else fails, consider installing a direct vent gas insert. These are installed with a dual chimney liner system; one liner brings combustion air down from the outdoors while the other vents the gas fumes.
HOW TO CLEAN SOOT STAINS
Once you've addressed the cause of soot, it's time to clean up those soot stains.
First, put down a drop cloth to help keep drips from landing on your hearth and creating more stains and creating an even bigger mess to clean up. You'll also want to don some gloves for this project.
If the facing on your fireplace is a smooth material like marble or granite then a mixture of vinegar and water and a cotton rag may do the trick.
A porous material like brick or stone is more difficult to clean. Step one is to rub with a dry cotton rag to clean any loose surface stains. If you have a shop vac then see what you can clean off using the brush attachment. (We put the vac outside and bring the hose in through a nearby window when possible to keep soot from exhausting out of the back of the vaccuum). Next comes the heavy duty cleaning. The best product for the job is Spic & Span, which contains trisodium phosphate (TSP). Mix according to directions and use a heavy duty bristle brush and scrub away, working in small areas. Wipe off excess moisture with a dry rag as you go. Because TSP is a very heavy duty cleaner, wear long sleeves and goggles when working with it. If any gets on your skin then clean it off immediately. Make sure the room is well ventilated. TSP will stain metal, rugs, tile or anything it touches so tape off and protect your entire work area. Work slow and clean any spills immediately.
Allow the bricks or stone to dry and see how well this worked. Severe stains may require repeating the cleaning process.