Calcium hydroxide (Ca(OH)₂) is a versatile, highly alkaline inorganic compound. It appears as a soft, white, odorless powder formed when calcium oxide (quicklime) is mixed with water in a process called slaking. Although only slightly soluble in water, its saturated solution, known as limewater, is a strong base with a high pH of around 12.4. Its role as an inexpensive and effective neutralizing agent makes it useful across numerous industrial and consumer applications.
Common Names and Primary Applications
Calcium hydroxide is widely referred to as slaked lime or hydrated lime, terms that denote its production via the hydration of quicklime. In the construction industry, it is commonly labeled as builder’s lime or masonry lime, where it is a traditional component in making mortars, plasters, and renders. When mixed with sand and water, it acts as a binder in masonry work.
For agricultural and gardening purposes, it is applied as a liming agent to adjust soil acidity, which improves nutrient availability and overall soil quality. In food processing, it is known as pickling lime or edible lime. It is used as an additive to regulate acidity and improve the texture of certain foods. For instance, it is used in the traditional process of nixtamalization for corn, which increases the bioavailability of niacin (Vitamin B3). Pickling lime is also used to help cure and crisp vegetables.
Forms, Grades, and Packaging Types
Calcium hydroxide is primarily sold as a fine powder, which is the standard form known as hydrated lime. This dry powder is ready for immediate use in applications like soil treatment or mixing into dry construction materials. When mixed with water, it can form a slurry or a viscous paste, sometimes called lime putty, which is a traditional form used in fine plasterwork.
The required purity level, or grade, is determined by the intended application. Technical or Industrial Grade is the most common and is suitable for construction, water treatment, and general chemical manufacturing, generally having a purity of 90% to 98%. Applications involving consumption require a much higher standard, necessitating a Food Grade (FCC) or USP (United States Pharmacopeia) Grade. Food Grade calcium hydroxide, often identified by the E-number E526, must meet stringent purity standards for use in food processing and supplements. Packaging varies significantly, ranging from small, multi-ounce containers for specialty food use, to 50-pound bags for construction and agriculture, and large bulk containers for industrial purchasers.
Retail and Specialized Purchase Locations
The most appropriate location for purchasing calcium hydroxide depends on the required quantity and grade. For small consumer quantities intended for general household, gardening, or construction projects, physical retail locations are the best option. Hardware stores and home improvement centers typically stock the technical or builder’s grade in 40- to 50-pound bags, often labeled specifically as hydrated lime or builder’s lime.
Garden supply outlets and agricultural cooperatives are reliable sources for agricultural-grade material, sold in large bags for soil amendment or pH adjustment. For these general-purpose purchases, use the common name “slaked lime” or “hydrated lime” when inquiring, as store personnel may not recognize the chemical name.
Conversely, higher-purity material, such as Food Grade or Reagent Grade, requires specialized suppliers. These grades are best sourced from online chemical suppliers, laboratory supply companies, or specialty food ingredient vendors. These specialty retailers offer smaller, precisely weighed quantities, often with purity certifications like FCC or Kosher. Large-volume purchasers, such as construction firms or water treatment facilities, obtain industrial-grade product directly from chemical distributors or specialized lime manufacturers who offer bulk delivery options.
Essential Safety and Storage Guidelines
Given its strong alkaline nature (pH exceeding 12), calcium hydroxide must be handled with appropriate safety measures to prevent chemical irritation. Direct contact with the powder can cause irritation or burns to the skin and eyes, and inhaling the dust can irritate the respiratory system. Users should wear personal protective equipment, including safety goggles or a face shield, protective gloves, and a dust mask or respirator to avoid inhaling fine particles.
Proper storage is necessary to maintain the product’s effectiveness and ensure safety. Calcium hydroxide should be stored in a cool, dry place in a tightly sealed container. This is because the compound can absorb carbon dioxide from the air and moisture, which causes it to degrade and form calcium carbonate. Containers must be kept away from strong acids and oxidizing agents, as contact with these substances can cause unwanted chemical reactions.