Crystallisation

The mechanism

Crystalline products contain active ingredients that react with the moisture and with the free lime present in the cementitious matrix. The reaction generates insoluble crystals that progressively occupy pores and capillaries, reducing capillary absorption and the permeability of the mass.

The distinctive property is that the reaction is dormant. In the absence of water the active ingredients stay inert; when water reappears — even years later, even at a different point — crystallisation resumes. This is what produces the self-healing of cracks, declared by manufacturers up to 0.4 mm for straight cracks and 0.5 mm for branched ones.

In the mass or on the surface

The admixture is dosed at the batching plant, as a percentage of cement weight, and waterproofs the entire volume of the pour. This is the route for new structures: no layer to apply, no surface to prepare, no risk of site damage.

The penetrating slurry, instead, is applied to the surface of concrete already in place: the active ingredients migrate into the matrix by diffusion. This is the renovation route, and it also works against negative pressure.

The variants available

Commercial products combine crystallisation with a second function. The version with an integrated corrosion inhibitor actively protects the reinforcement, useful in aggressive or marine environments. The hydrophobic version adds an immediate reduction in water absorption, which precedes crystal formation. The plasticising version, classified under EN 934-2:T2, allows a reduction of mixing water and therefore a direct improvement in durability.

They come in powder form, including water-soluble bags that go whole into the mixer, and in liquid form for automatic dosing at the plant.

What it does not do

Crystallisation makes the mass of the concrete waterproof. It does not seal construction joints, which are interfaces between two pours and must be treated with waterstops; it does not close cracks wider than the declared value; it does not replace structural design aimed at limiting cracking. A complete system uses crystallisation as the base and waterstops as the complement.