For the cleaning process, you can use simple water, or in the case, the dirt is more resilient soap water. Use a wire brush or stiff-bristled brush and soak it in the water/ soap water before using it. If the soap water isn’t enough you can take something stronger like trisodium phosphate (TSP). For that mix half a cup (120ml) and one gallon of water (3.8 l). Then dip your brush into the solution before scrubbing the brick. Always make sure to use safety goggles as well as gloves when using TSP.