Every waterproofing method discussed so far is applied after the concrete has cured — a coating on the surface, a membrane laid over it. Integral, or crystalline, admixtures take a different approach entirely: they're dosed directly into the concrete mix at batching, so the waterproofing becomes part of the structure rather than a layer sitting on top of it.

Crystalline admixtures work by reacting chemically with the water and unhydrated cement particles already present in the mix. That reaction grows needle-like crystals that fill the capillary pores throughout the concrete's depth, not just at the surface. Because the reaction is triggered by moisture, some crystalline products retain the ability to 'reactivate' and grow new crystals if a fresh crack later lets water in — a genuinely useful form of self-healing for structures that are hard to access for repair, like buried tanks or foundation walls.

The obvious appeal for new-build work is that there's no separate waterproofing trade, no membrane to protect during subsequent construction, and no exposed layer that can be punctured by rebar fixing or formwork strikes. The trade-off is that it only protects the concrete itself — construction joints, pipe penetrations, and cracks beyond a certain width still need a waterstop or separate joint sealant, since an admixture can't do the job of a physical barrier at a joint that was never continuous concrete in the first place.