Sandblasting is an abrasive method of removing surface matter – usually paint – by using the pressure of fine grains of sand traveling at high speed. Also called abrasive blasting, this process is also used to smooth a rough surface, roughen a smooth surface, shape a surface, or remove surface contaminants. Pressurized air or water, or a centrifugal wheel, may used to propel the abrasive material.
Silica sand is the most commonly used type of mineral abrasive, although the term sandblasting has also been applied when materials other than sand are used. Sand tends to break up quickly and produce large quantities of dust, thus exposing the operator to a debilitating lung disease known as silicosis. To counter this hazard, silica sand for blasting is often coated with resins to control the dust. Sometimes, sand is substituted with other kinds of small and uniform particles such as walnut shell, coconut shell, powdered abrasives, steel grit, and copper slag. Safety laws have also mandated the use of protective gear and ventilation during sandblasting.
The sandblasting process was first developed and patented in the United States in 1870. Initially, it was used for cleaning large surfaces, such as ship hulls and even the Golden Gate Bridge. It was also used to prime a surface before the application of paint or sealant. The sandblasting prevented dirt or bubbles from being trapped in the paint layers. By launching small bits of abrasive at the surface at a high speed, imperfections are loosened and can then be easily washed off, creating a smooth surface upon which to lay the new layer of paint.
Sandblasting requires special equipment consisting of an abrasive, an air compressor, a blaster nozzle, and a collector to catch excess dust. There are many different types of abrasives, including minerals such as aluminum oxide, white aluminum oxide, and coal slag. There are also synthetic abrasives such as plastic and pumice, as well as biodegradable abrasives such as corn cobs, walnut shells, and baking soda. Crushed glass grit or glass beads have also been used.
Types of sandblasting media:
- Aluminum oxide – This is one of the hardest abrasive materials available, second only to diamond. It is very abrasive and cuts through metals quickly. It also produces very little dust, and is the ideal and safe choice when working with hard metal surfaces. When used on metal surfaces, it creates a matte-looking finish.
- Coal slag – Taken from power plants that are run by coal, slag is often used for general maintenance and for making repairs on ships and bridges to remove paint and various coatings.
- Plastic grit – This is a gentler synthetic blasting media and comes in various shapes and sizes. It is often used to restore cars or other items because it will strip the body of paint, but will not damage the surface underneath. Pumice is also a soft type of media that will not damage surfaces below a layer of paint.
- Silica sand – Among the most popular sandblasting media types, it is inexpensive and effective. But it also creates a significant amount of dust and health hazard.
- Crushed glass grit and glass beads – Recyclable and natural, glass is economical, too. In general, the smaller the glass pieces, the slicker the surface will be. The beads are commonly used to clean calcium build-up on tiles around hot tubs and swimming pools. In addition, either type will clean fiberglass, lighten grout, and remove rust or mold.
- Corn cobs, walnut shells, and baking soda – These are the gentlest, least expensive and most environmentally friendly types of media. The corn cobs are used on wood to clean structures such as barns, homes, and fences, before they are painted. In addition, the corn cob grit will clean areas affected by smoke damage and absorb grease or other substances. It can also be used to clean or polish thin metals such as jewelry, engine parts, or springs. Walnut shells are used to make a biodegradable sandblasting media grit. This type of grit is inexpensive but also effective in cleaning and polishing sensitive items like electronics, aircraft turbines, historic architectural structures, and car parts. Baking soda is often used to clean and restore surfaces such as stone or marble and remove graffiti, mold, and rust.
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