Combine 1 part hydraulic cement with 3 parts of masonry sand in a bucket. Mix together with a trowel until well-blended.
Pour water from a jug into the bucket, moistening the dry mixture. Stir the mixture with the trowel until it reaches a pancake batter consistency.
Wipe the crack or hole in the basement wall with clean, dry rags until dry or nearly dry. Spread the mixture into the hole or crack with the trowel.
Allow the cement mixture to dry for about 24 hours, then apply a coat of concrete sealer over the patch with a paintbrush, overlapping the patch a few inches on each side and let dry to finish the repair.