Brush the shattered area of the brick wall lightly with a wire brush to remove loose pieces. The goal is to make as solid a base as you can to which the grout can bond.
Combine warm water and grout mix in a plastic bucket until it is the consistency of thick oatmeal.
Spread the grout mix over the damaged area of the brick using a small masonry trowel. Fill in depressions and holes using the top of the trowel to press in the mix. Use the side of the trowel at more of an angle to the surface to smooth the grout and remove excess. Don't leave chunks of grout on the wall. Allow the grout to dry for 24 hours.
Brush on a grout sealer to the repaired area using a paint brush. Completely cover the repair with sealer.