Sodium silicate has emerged as a popular compound that enjoys widespread usage. It is produced by melting high purity sand with soda ash (sodium carbonate) in high temperature furnaces. The mix proportions may vary.
The resulting silicate powder contains oxygen-silicon polymer with water lodged in molecular matrix pores. It is readily soluble in water to form an alkaline solution. In fact, the water-dissolved powder forms sodium silicate solution or what is popularly known as water glass.
Sodium silicate carries many useful properties that are not shared by other alkaline salts. Accordingly, it enjoys a wide range of applications in different industries – detergent manufacturing, construction products, petroleum processing, waterproofing, binders for concrete and plaster, metal mold making, unique coatings and antique finishes, deflocculant for clay slip and so on.
The high silica polymer content delivers excellent physical and chemical properties that make sodium silicate function very well as a high temperature adhesive. The polymers remove small amounts of water when converting from liquid to solid. Moreover, the solution can expand and make contact which gives the compound a superior advantage in bonding applications.
In fact, water glass is the only inorganic adhesive that offers high strength and sets rapidly. This combined with the low cost of water glass makes it a common adhesive in many industrial and consumer applications.
How to use?
The solution comes as ready to use. For special applications, certain additives such as clay, casein and other inorganic materials can always be added to the water glass.
All you have to do is apply a thin, continuous layer on or between surfaces of materials to be bonded. It can effectively bind various materials such as metals, glass, wood, ceramics, fibrous materials such as paper and fiberglass and even particles such as refractory materials. However, it does not work well on plastics, per se.
What happens?
The sodium silicate solution will dry quickly to form a tough, tightly adhering inorganic bond or film. The rigid layer is the last word in optimum adhesion as it stays strong, permanent and is highly resistant to tearing. To add to this, the sodium silicate is also odorless, non-toxic, environment-friendly, non-inflammable as well as resistant to moisture and temperatures up to 3000 F.
The same water glass can also seal concrete, plaster and stucco surfaces as well. A thin coat applied on unpainted plaster or concrete will dry out to effectively bind the silicate to the surface. The silicate film reduces the porosity, thus making the material water-repellant and resistant to wear. However, the silicate treatment should be done only after the concrete or plaster has completely cured.
Little wonder then that water glass enjoys great patronage in the arts. Mold makers and casting artists also use water glass to make sand molds and cores, to thin their clay slips, to seal plaster casts and also to lend an antique finish on ceramic artworks. The adhesive properties also prove particularly useful for artists!
