When applied correctly, the best caulk for waterproofing concrete will effectively seal gaps in the foundation and between the foundation and wall to stop water infiltrations. Moisture in the foundation can widen existing cracks, causing expensive damage that, in extreme cases, could threaten the structure's integrity. To avoid these potential issues, here is a list of common sealant application errors and how to avoid them, as well as considerations to guide your concrete sealant selection.