What happens next?

How to clean the exterior of your garage
Use a jet wash machine to clean the walls of the garage.
This will get rid of the build-up of dirt and make the brickwork look fresher. However, don't use the jet wash machine on the garage door or the windows as this may cause damage to these more fragile surfaces.
Remember that these machines can be extremely powerful, so you might take some of the cement away when cleaning the brickwork. Once the walls have been treated, use a cloth and a bucket of warm soapy water to clean the windows.