Last winter's heavy rains seeped into my garage through a retaining wall of concrete and cinder block, which is also the exterior wall of the garage. Water also seeps in where the adjoining stucco wall and the ceiling meet. Roof coating does not stop this latter leak. I wish to waterproof the retaining wall first and then reroof, if necessary. I hve been advised to first coat the retaining wall with cement plaster; then, after it has dried, to apply a water seal. Is this what you would do? Richard Sinclair Ventura, California
The leak where the ceiing joins the wall sounds like a flashing problem, if not in the roofing itself. A competent roofer should inspect the leak up there and, after locating the cause, advise you as to remedial measures.
A new roof may not be necessary, Depending on its age and condition.
As to waterproofing the retaining wall, applying a thick coat of cement plaster on the outside of the masonry below grade will help. After the coating is thoroughly dry, apply a waterproofing agent or sealer. However, remember that coatings of the ordinary kind may last only a few years and then cease to be water-resistant, or they may simply disappear.
One coating that the manufacturer says will last indefinitely is made by Sealwall Products, 36300 Lakeland Boulevard, Eastlake, OH 44094.
Note: The cement plaster should be troweled on the retaining wall, ideally to the depth of the footing -- or at least below floor level. Footing drains may need to be installed to carry off the rainwater that might collect below the floor level outside.
Do what you can to prevent the water from migrating or standing in the earth adjacent to the retaining wall.