[amayze]

The father of one of my customers, left his battery charger on his car and set both the garage & the car on fire, before he was admitted to an OAP home.

The garage is completely empty, but she has asked if I can jet wash the walls - is this possible ? 

[concept]

If you answered your phone, I'd tell you 

[BDCS]

Yes but you'll need a pre spray to degrease the area first, hot will also help

[jessicasmith]

Yes you can clean it by using chemical dry sponge. Wipe the stain with the dry sponge and no moisture is needed. A chemical dry cleaning sponge is a perfect way for removing soot from wall.

[John Kelly]

Yes you can clean it by using chemical dry sponge. Wipe the stain with the dry sponge and no moisture is needed. A chemical dry cleaning sponge is a perfect way for removing soot from wall.

Not from this kind of fire its not. Fire residues come in two forms, wet & dry. Dry residues are created when materials such as wood or paper burn. They give off a light dry soot. This can easily be removed by using a Latex Sponge (don't why they are called chemical sponge as there is no chemical in them).
Wet residues are caused when plastics, oils, paint, manamade fabrics, electricals etc are burnt. These are a different kettle of fish and latex sponges may take some of the residues off but the only way to fully remove the excess residue is to spray with a high alkaline detergent, preferably with a deodouriser mixed in, then wipe with a cloth. White terry towel peices are the best for this. You need to use a clean cloth as soon as it becomes dirty otherwise you are just spreading the contamination.

[Blast Away]

Sponges? The OP hasn't even mentioned what type of surface the walls are and already the answer is a sponge?

No wonder people stop coming on here.