Question 1

When is interior cementitious tanking enough on its own?

Accepted Answer

It is enough when the hydrostatic pressure is moderate, the substrate is sound masonry or concrete, and we can hack back to a clean profile that the tanking will bond to. A Wynberg basement storeroom with intermittent winter damp through a single wall is a textbook case — three coats of Sika 1 or Drizoro Maxseal Foundation on a properly prepared substrate will hold for fifteen to twenty years. The minute the wall is structurally cracked, the pressure is high enough to spall the coating, or there is visible standing water during winter, tanking alone is the wrong call and we move to a managed-water solution.

Question 2

When do you need a cavity drain membrane plus a pump instead?

Accepted Answer

When the floor cannot be raised, the water table is genuinely above the slab, or the building has live structural movement. We see this constantly in Green Point and Sea Point converted-basement garages where the original 1960s construction sits below the modern water table — there is no realistic way to block that volume of water, so we install Delta MS or Newton CDM membrane on the walls and floor, lay a perimeter drainage channel, and pipe everything to a twin-pump sump with battery backup. The space stays dry, the water is managed, and any future seepage simply runs into the channel instead of into your finishes.

Question 3

I have seepage on a Bantry Bay cliff-side retaining wall — what do I do?

Accepted Answer

Cliff-side retaining walls in Bantry Bay almost always need a two-part fix. First, on the inside face, we apply a crystalline system like Xypex Concentrate so the concrete itself becomes waterproof and any new hairline cracks self-seal with future moisture exposure. Second, we install a horizontal weep system and a vertical drainage layer behind the wall where access permits — usually possible on the upper terrace, rarely possible against the slope. Where the slope side cannot be reached, we accept that we are managing rather than blocking the water and add a discreet perimeter channel at the wall base to catch anything that finds a path through.

Question 4

Why is exterior excavation so rarely the answer on an existing home?

Accepted Answer

Because the cost-benefit collapses the moment you account for landscaping, paving, boundary walls, neighbour interfaces, and the risk of undermining the existing footing during the dig. On a Constantia valley cellar with mature gardens above it, exterior excavation might mean tearing out a R200,000 landscaping scheme to install a R60,000 membrane — and you still need engineering input to shore the excavation safely. We reserve positive-side exterior work for new builds, full structural basement conversions where the slab is being recut anyway, or the rare case where a single accessible elevation has failed and the rest of the house is fine.

Question 5

How does a crystalline system like Xypex or Penetron actually work?

Accepted Answer

Crystalline products are cement-based slurries (or concrete admixtures, for new pours) that contain reactive chemicals which migrate into the capillary network of the concrete, react with calcium hydroxide and moisture, and grow insoluble crystals deep inside the pore structure. Those crystals physically block water passage but allow water vapour to pass, so the concrete still breathes. The reaction is dormant until moisture appears, then reactivates — which means hairline cracks up to about 0.4mm self-heal over time as new water arrives. It is the only system we use that becomes part of the concrete rather than sitting as a coating on top of it, which is why it tends to last the life of the structure.

Question 6

What about a Constantia cellar with garden-level damp — can it be fixed without disturbing the garden?

Accepted Answer

Yes, almost always. The standard solution for a Constantia valley garden-level cellar is interior cementitious tanking on the affected walls, plus a discreet perimeter french drain installed inside the cellar at the wall-floor junction to relieve hydrostatic pressure. Where the cellar has a finished floor we want to preserve, we substitute a cavity drain membrane and sump to keep the existing floor intact. The garden above stays untouched. Done correctly with the right substrate prep and a proper drainage discharge, this lasts fifteen to twenty years without recoating.

Question 7

How long does this work actually last?

Accepted Answer

Crystalline systems last for the life of the concrete because they are integral to the matrix, not a surface coating. Cavity drain membranes carry 25 to 30-year manufacturer warranties when paired with serviced sump pumps. Cementitious tanking realistically gives you 15 to 20 years before any recoating is needed. Bentonite membranes installed externally last 25+ years when correctly backfilled. We back every installation with our 10-year workmanship guarantee, and on habitable basement conversions we provide engineer-signed certification for council sign-off and insurance purposes.

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