You need to excavate your stem walls to at least one-foot below finish grade (ground level). You will get best results if you excavate all the way to the top of the footing. Next, power wash your stem-walls clean. This step is crucial to the preservation of your wall; the better you clean your wall for this project, the better your wall will withstand future moisture and erosion. Then, purchase a product called Thoro-Seal Foundation Coating. Following the manufacturer’s directions, apply Thoro-Seal with a thick mortar wash brush and then smooth it out with a trowel, or apply directly with a trowel.