CMU wall waterproofing

A homeowner building a house in New Mexico with a concrete block (CMU) crawl space foundation asked where to put waterproofing on the garage wall. The wall height varies from 3 to 7 rows of block because the lot slopes, and the garage side will be backfilled with soil to within 6 inches of the top of the wall. The homeowner had gotten conflicting advice: waterproof the inside only, the outside only, both sides, or the inside plus a drainage mat on the outside.

Two people who answered pointed to the same answer: waterproof the outside of the wall, not the inside. One recommended pairing a waterproofing membrane or liquid coating (not a cheaper "damp-proofing" product, which does less) with a drainage board or mat, plus footing drains that carry water away from the base of the wall to daylight. Once the outside is sealed against water, whatever finish goes on the inside is mostly cosmetic.

The other point raised was structural, not just about moisture. With almost 6 feet of soil pushing against one side of the wall and nothing but a slab on the other, that kind of unbalanced backfill height often requires reinforcement inside the block — steel rebar and grout in the hollow cores, horizontal wire reinforcement, or thicker block. Standard 8-inch block without reinforcement is likely not strong enough on its own. This is the kind of detail a project's architect or engineer needs to specify, since the right reinforcement depends on soil type and local seismic requirements, not just the waterproofing method.