We have mold in our basement and garage.  The nold is attached to the
interior walls.  There is not any pools of water- there is just poor
ventilation.  The house is 50 years old and the walls are cinder
block.  We are going to dig upt the dirt on the exterior walls, and
dig down about 8-10 feet across the exterior wall.  We are then going
to seal  the wall with a sealant.

What would be the best sealant to apply to help prevent the moisture
from seeping through the cinder block walls.  Also, what is the best
way to prepare the exterior wall and to apply the sealant.

Hi!  You should make sure that the side of the block wall that you are
treating is clean (use a brush and water), let it dry, and then use a
foundation sealer.  You can buy this from a concrete block suppy
company, or from a home improvement store.
Once you get it sealed, you need to find some way of ventilating your
affected area to prevent mold from returning.
Good luck!

thank you very much, appreciate your comment