Advertising Krystol or Xypex as an "internal membrane" is deceptive. They work to seal porosity and cracks in much the same way as normal concrete pipes sometimes stop leaking over a period of time by autogeneous healing. There has to be moisture present, and thus leakage, for the products to even start to work. I have several times been asked to investigate why slabs over basement carparks, cast with Xypex admixture, are leaking. The slabs leak because they have restraint shrinkage cracks, have not been built as water retaining structures, and do not have a membrane. Not a good thing to have alkaline leakage onto a lot of BMW and Mercedes automobiles in a residential highrise carpark.
When these products originally came on the market, the companies insisted on strict adherence to minimum reinforcement, minimum cement content and maximum w/c ratio, and wet curing...all to be supervised by their own personnel. In other words, they required quality in construction which would largely make their admixture redundant. These specifications appear to have disappeared from the current manufacturers' literature.
