Textbook waterproofing says treat the exterior. Real Bay Area properties often say otherwise — a shared wall in San Francisco, a protected oak in Atherton, or a hardscaped courtyard can each make excavation impractical or genuinely impossible. In those situations, interior methods are not a shortcut. They are the correct engineering response to a constrained site.
Crack and joint injection
Injection fills a crack through the full depth of the wall rather than sealing its surface. Ports are set along the crack and resin is pumped in under pressure until it travels the wall thickness and seals the entire path.
Polyurethane resin is used for actively leaking cracks — it reacts with water and expands to fill the void, which is exactly what you want in a wet crack. Epoxy is used where the crack is dry and structural bonding is the goal, since cured epoxy is stronger than the concrete around it.
Curtain grouting
Curtain grouting goes a step further: grout is injected through the wall so it forms a barrier in the soil on the outside face. In effect it creates a section of exterior waterproofing without anyone digging to reach it.
It is well suited to walls where water is entering across a broad area rather than through one identifiable crack, and to situations where the outside face is genuinely unreachable.
Interior drainage systems
Where water volume is high, blocking it entirely from inside is fighting physics. Interior drainage takes the opposite approach: intercept water at the cove joint, route it through a channel around the perimeter, and discharge it via a sump.
This does not keep the wall dry, and it is not meant to. It keeps the occupied space dry and relieves the hydrostatic pressure that would otherwise push coatings off the wall — which is why drainage and negative-side coatings are so often specified together.
- Perimeter channel installed at the floor-wall cove joint
- Sump basin and pump sized to the expected water volume
- Battery backup for storm-season reliability
- Discharge routed well away from the foundation
Negative-side coatings
Cementitious and crystalline coatings applied to the interior face resist moisture moving through the wall. Crystalline products are the more interesting option — they react with moisture in the concrete and grow crystals that block the capillary pathways within the slab itself.
Their limit is hydrostatic pressure. Under sustained pressure with no drainage relief, any negative-side coating can be pushed off the substrate. Pairing them with drainage is what makes them durable.
Knowing when interior work is the wrong answer
Interior methods manage water that has already entered the wall. They do not protect the concrete or its reinforcement from long-term saturation. Where excavation is genuinely feasible and water volume is significant, exterior work remains the better long-term investment.
An honest assessment says so. We would rather tell you the exterior is worth the disruption than sell an interior system that manages a symptom you will be revisiting.