Waterglass is a common name for sodium silicate, a compound made from sodium, silicon, and oxygen that dissolves in water to form a thick, syrupy liquid. It has been used for over a century in applications ranging from preserving eggs to sealing concrete, fireproofing buildings, and even patching cracked engine blocks. The name “waterglass” comes from its glassy appearance when it dries into a hard, transparent solid.
What Waterglass Actually Is
At its core, waterglass is sodium and silica (the main component of sand) dissolved in water. In dry form, it looks like a white powder or flakes. When mixed with water, it becomes a viscous, alkaline solution that can range from thin and watery to thick and gel-like depending on concentration. As the water evaporates, it hardens into a rigid, glass-like material.
This transformation from liquid to solid glass is what makes waterglass so versatile. It bonds strongly to porous surfaces, resists heat and flames, and creates an airtight seal. You can buy it at hardware stores, chemical suppliers, or online, typically as a liquid solution ready to use.
Egg Preservation: The Classic Use
The most well-known traditional use of waterglass is preserving fresh eggs. Before refrigeration was widespread, people would submerge unwashed eggs in a diluted waterglass solution (roughly one part waterglass to nine or ten parts water). The solution seals the tiny pores in the eggshell, preventing air and bacteria from getting in and moisture from getting out. Eggs stored this way can last six months to a year at cool room temperature.
This method works only with unwashed eggs that still have their natural protective coating, called the bloom, intact. Store-bought eggs in the United States have already been washed and won’t seal as effectively. If you keep backyard chickens or can source farm-fresh unwashed eggs, waterglass preservation is straightforward: mix the solution, pour it into a food-safe container, and gently lower the eggs in. They need to stay fully submerged. Sodium silicate does have FDA recognition as a food-contact substance, listed under multiple food additive and GRAS (Generally Recognized as Safe) regulations.
How It Works in Construction
Waterglass is widely used as a concrete sealer. When applied to a concrete surface, the sodium silicate soaks into the pores and reacts with the calcium compounds naturally present in the concrete. This reaction produces a dense gel that fills microscopic gaps, hardens the surface, and makes it far more resistant to water penetration. The treated surface becomes denser and more durable without changing the concrete’s appearance.
In building construction more broadly, waterglass serves as a fireproofing agent. Because it’s completely inorganic, it doesn’t burn. Coatings and adhesives made from sodium silicate are inherently flame resistant and also resist mold, bacteria, and pest damage. This makes it valuable for insulation bonding, refractory cements (materials designed to withstand extreme heat), and acid-proof construction where chemical resistance matters.
Industrial and Manufacturing Uses
The biggest industrial use of waterglass is as an adhesive, particularly for paper and cardboard. Corrugated cardboard boxes are frequently bonded with sodium silicate adhesives because they’re cheap, fast-setting, and strong on porous materials. Beyond packaging, waterglass adhesives bond wood, metal foils, and glass to porous surfaces.
In metalworking, sodium silicate is used to make foundry molds and cores for casting metal parts. The waterglass binds sand into a rigid shape that can withstand molten metal, then breaks down for easy removal after the casting cools. It also seals porosity in sand castings, filling tiny voids that would otherwise weaken the finished part. Abrasive wheels, like grinding discs, use waterglass as a binder to hold abrasive particles together.
The “Liquid Glass” Engine Fix
You may have seen products marketed as “liquid glass” engine sealers at auto parts stores. These contain dilute sodium silicate, sometimes mixed with fine copper particles. The idea is simple: you pour the solution into your cooling system, and it circulates with the coolant. When it reaches a crack or leak in the radiator, engine block, head gasket, or heater core, the particles bridge the narrowest point of the gap and slow the flow.
Once the sodium silicate is lodged in the crack, the combination of engine heat and exposure to outside air causes it to solidify into a hard, crystalline material that resembles glass. This creates a permanent seal over the damage. It’s a temporary or emergency repair rather than a substitute for proper mechanical work, but it can buy significant time on small cracks and pinhole leaks. The same principle was used in government “Cash for Clunkers” programs, where sodium silicate was poured into engines to permanently disable them.
Other Everyday Applications
Waterglass appears in places most people wouldn’t expect. In detergents, it acts as a builder that softens water and boosts cleaning power. Silica gel packets, the little “do not eat” desiccants packed with electronics and shoes, are made from sodium silicate. It’s used in water treatment to prevent corrosion in metal pipes, and in the paper industry to improve brightness and ink absorption.
Artists and crafters use waterglass to create crystal gardens (those kits where colorful mineral “trees” grow in a solution). When metal salts contact the sodium silicate, they form thin membranes that grow upward through osmotic pressure, producing branching, tree-like structures. It’s also used as a binder in some paints and coatings, particularly those designed for masonry surfaces where breathability and fire resistance matter.
Safety and Handling
Waterglass in liquid form is strongly alkaline, similar in pH to household bleach or oven cleaner. It can irritate skin on contact and cause serious eye damage, so gloves and eye protection are worth wearing when you work with it. If it dries on your hands, it leaves a slippery, soapy feeling that’s hard to wash off. Spills on countertops or floors should be cleaned up quickly, since the dried residue bonds tenaciously to most surfaces. In diluted form, as used for egg preservation, it’s much milder but still worth handling with basic care.
Stored properly in a sealed container, waterglass solution has a long shelf life. Exposure to air will cause it to thicken and eventually solidify as the water evaporates, so keeping the container tightly closed matters. If your solution has thickened but hasn’t fully hardened, you can sometimes thin it by adding water and stirring, though heavily gelled product may not recover well.