Inorganic Silicate Concrete Densifier

Concrete densifiers are applied to concrete to penetrate and fill pores and voids through a process of crystalline growth. They react with calcium hydroxide in the concrete or carbon dioxide in the air to create a precipitate that prevents water penetration and prevents the formation of dust on the surface. This reaction differs from that of penetrating concrete sealers, because although it physically prevents water penetration it is not designed to make the substrate water-resistant. Furthermore, when concrete densifiers react with concrete they do not release volatile organic compounds (VOCs) like penetrating concrete sealers do. 

Concrete densifiers are based on several different inorganic silicate chemistries and include sodium silicate, potassium silicate, lithium silicate, magnesium silicate, magnesium fluorosilicate, and colloidal silica formulations. This Common Product describes a lithium silicate concrete densifier. Lithium silicate concrete densifiers are typically applied to concrete with a sprayer, and can be applied before a concrete sealer is applied. Coverage varies widely depending on the porosity of the concrete. These products are seen as advantageous over potassium and sodium silicate formulations because they can prevent alkali-silica reactions (ASR). ASR occurs in the presence of water in high pH environments where hydroxyl ions from hydraulic cement react with silica-based rocks and minerals present in some aggregates, which can lead to expansion and cracking of the concrete. 

Concrete densifier formulations are relatively simple, but they can contain additives in addition to water and the inorganic silicate. Some products add silicone-based water repellents, but these were not found to be common. Other products indicate that a wetting agent (also referred to as a surfactant) is used to allow for deeper penetration of the densifier into the pores of the concrete. There is very little disclosure on what type of surfactants are used, but patents for some product formulations indicate that fluorinated surfactants, silicone-based surfactants, and alkyl phosphates could be present in some products.