2SiO3 (in water- free state). It is a colorless to white, hygroscopic solid (water attracting!), quite soluble in water.
Water glass is made by melting sand with sodium carbonate at 1,400°C, a process that is very similar to the production of glass, hence the name.
The melt product is then added to water and the soluble parts go into solution.

waterglasWater glass is a viscous, liquid agent that makes various objects watertight. It is water repellent, pores narrowing, vapor diffusion and interrupts capillary action.

It is used in the soil where it the rising ground water effectively stops.
Water glass is also used to make floors, walls, basements and / or concrete walls waterproof. You can apply it with a brush or roller. With new work by mixing it in concrete or grout and so it creates a watertight finishing product.
One can also use it to close (pottery) vases or stone that leaks.
You find it in cleaning products, where it is listed as sodium (or sodium silicate) on the packaging.
It is also used in adhesives and binders, cardboard.
Upon acidification is silica gel created, a form of silica that is mainly used in packaging to reduce the relative humidity.

The solution in water is a strong base. So it reacts violently with acid and is corrosive to aluminum and zinc. In contact with these materials, hydrogen gas is formed. Sodium silicate reacts with halogens, creating the potential for fire.