To give brick work of any kind a pressure wash requires a lot more attention to detail than normal. The nature of brick, porous and fragile, means that a great deal more care has to be taken in the selection of the spray strength. More time needs to be spent examining the job before work can start.
Step 1 – Check the External Brickwork
If the external brickwork has been exposed to weather as well as heat from the inside there is a good chance that many bricks will be cracked. A soft brush should be used to sweep the bricks down to remove any surface dust. The dust might also disclose mortar joints that are in danger of failing.
Step 2 – Check the Internal Brickwork
The internal brickwork will have been affected by extremes of heat and you could find, once again, that there are cracked bricks and decaying or crumbling mortar. If the fire has been dirty there may well be layers of soot to clean off some of the brick chimney. You will have to decide to which point the chimney is going to be cleaned with the pressure washer.
Step 3 – Clean the Chimney
Before you start any pressure washing you will need to clean the chimney with rods and a brush. The removal of soot at the base of the chimney and the vibrations set up by the pressure sprayer could loosen the soot in the chimney and cause it to fall.
Prepare to mop up the water as it comes down the chimney from the pressure washer. You could use the soot to create a barrier to stop the water flowing from the chimney front.
Step 4 – Clean the Inside of the Chimney
Once you have decided how much of the chimney is to be pressure washed you can make a start. Don’t use high pressure – no more than 400psi – and use a fan spray. This will remove most of the loose dirt and soot without breaking into the brickwork and washing out parts of bricks that have cracked but not yet fallen. Start at the top and work your way down spraying from side to side.
The fire box should be cleaner than the rest of the chimney but clean the cheeks well and any fire bricks. If there is a small flue it would be best to clean that at another time with a flue brush - not risk washing any soot into a collection that could dry and block the flue.
Step 5 – Clean the Outside of the Chimney
The outside of the chimney should be in reasonable condition but start to spray clean at the top of the area and work your way down. Again, do not use high pressure. Use the side to side motion and keep the jet moving down the wall.
Once the chimney has been cleaned it may need a little re-pointing and the odd brick replacing to fill any gaps caused by the pressure wash.