Published
Most waterproofing products place a barrier on top of the concrete. Capillary crystalline products do not; they go into the concrete and work there. That difference also defines where they help and where they do not.
The chemistry
Concrete is far more porous than it looks. Even after hydration completes, interconnected capillary voids remain in the section and water travels through them.
Capillary crystalline products carry active chemicals that react with the free lime and moisture in the concrete. In the presence of water they form needle-like crystals inside those voids. As the crystals grow they block the voids and close the path water would take.
The key point is that the reaction needs water. The product lies dormant in dry concrete and reactivates when water arrives — which is why it can still work in a hairline crack that forms years later.
Where it leads
Its clearest advantage is working from the negative side. Because the waterproofing is not a film on the surface, water pressure cannot peel it away. That makes it almost the only option on basement and retaining walls whose outer face cannot be reached.
Its second advantage is durability: a membrane on the surface can be damaged by impact, UV or subsequent trades; a crystalline structure inside the concrete sits outside those risks.
Its limits
Capillary crystalline products do not bridge moving joints or widening cracks. The crystalline structure is not flexible; where there is structural movement you need a flexible joint tape or membrane.
The substrate also has to be porous. Applied over dense screed, tile or paint the product never reaches the concrete and does nothing at all. Opening up the surface is essential.