How Concrete Absorbs Moisture

And how to Stop It

Moisture is one of the most important factors behind the deterioration of concrete. Without it, most damage mechanisms simply don’t occur. Yet concrete’s porous structure readily absorbs water through microcracks and capillaries – allowing frost, chlorides, and contaminants to penetrate deep into the material. Understanding how this happens is key to understanding why concrete needs protection. This section explains how water travels through concrete and how Komsol’s mineral-based technology reduces that transport.

The Capillary Structure of Concrete

Concrete is primarily composed of cement, gravel or crushed stone, sand, water, and air. During the curing process, water is removed from the mix, forming a fine-meshed network of interconnected channels and pores – known as the capillary system. Once fully cured, typical structural concrete has a total porosity of roughly 10–15% (higher in air-entrained mixes). The higher the water-to-cement ratio (w/c) in the mix, the more porous the hardened concrete becomes – resulting in increased porosity and reduced density.

Shrinkage and the Formation of Cracks

Cracking occurs in all concrete, though to varying degrees and extents. One common cause is plastic shrinkage, which results from two simultaneous movements of water within the concrete mass: internal water migration toward the surface (dewatering), and surface evaporation. When evaporation outpaces internal water transport, the surface dries too quickly, increasing the risk of cracking. Some cracks are visible to the naked eye, while others require a microscope to detect. Spraying a fine mist of water over the surface often reveals microcracks clearly during the drying process.

Capillary Absorption and Liquid Transport

When concrete is exposed to water or other liquids, the fluid is drawn into the material through its capillaries, microcracks, and larger cracks by means of capillary action. The narrower the capillaries, the stronger the capillary pull. This transport occurs both horizontally and vertically – and can penetrate deep into the structure.

Silicate-Based Densification (C-S-H Formation)

Komsol Seal penetrates into the concrete’s capillaries, microcracks, and pores. Inside the structure, it reacts with calcium-bearing phases to form additional calcium silicate hydrate (C-S-H) gel (predominantly amorphous/semi-crystalline). This densifies the pore structure and reduces liquid water transport while remaining vapor-permeable – allowing internal moisture to escape by diffusion. Because the protection forms within the concrete rather than on the surface, it is inherently resistant to external influences such as abrasion, freeze–thaw cycles, and mechanical wear.

Demonstrated Penetration and Crack-Sealing Performance

Laboratory demonstrations show that silicate impregnation can penetrate capillaries and tight cracks. In tests where one concrete cube was treated from the top (simulating a floor) and another from below (simulating a ceiling), the treatment reduced liquid transport and sealed microcracks along their exposed length. In highly porous concrete (w/c ≈ 0.7), penetration depths up to ~30 mm have been measured. Actual penetration and sealing performance depend on mix design, porosity, moisture state, and application conditions.