Because of its weak basic properties, calcium hydroxide has many and varied uses:

• A flocculant, in water and sewage treatment and improvement of acid soils
• An ingredient in whitewash, mortar, and plaster
• An alkali used as a lye substitute in no-lye hair relaxers
• A chemical depilatory agent found in Nair
• A calcium supplement in mineral fortified baby formulas
• A chemical reagent
  • In Bordeaux mixture to neutralize the solution and form a long lasting fungicide
  • the reef aquarium hobby for adding bio-available calcium in solution for calcium-using animals such as algae, snails, hard tube worms, and corals (often referred to as Kalkwasser mix), and also to increase the alkalinity of the water
  • In the tanning industry for neutralization of acid, the liming of hides and skins and the flocculation of wastewater
  • In the petroleum refining industry for the manufacture of additives to oils (salicatic, sulphatic, fenatic)
  • In the chemical industry for manufacture of calcium stearate
  • In the food industry for processing water (for alcoholic and soft drinks)
  • Used in the separation of sugar from sugar cane in the sugar industry
  • Used in the processing of Norwegian lutefisk. Dried cod fish is soaked in a mixture of slaked lime and soda to produce a soft-fleshed fish fillet that is steamed or baked and served with potato lefse
  • Used in home food preservation in the making of pickles.
  • For clearing a brine of carbonates of calcium and magnesium in the manufacture of salt for food and pharmacopoeia
  • In Native American and Mesoamerican cooking, calcium hydroxide is called "cal". Corn cooked with cal becomes nixtamal which significantly increases the bioavailability of niacin, and is also considered tastier and easier to digest.
  • In chewing betel nut or coca leaves, calcium hydroxide is usually chewed alongside to keep the alkaloid stimulants chemically available for absorption by the body.
  • Similarly, Native Americans traditionally chewed tobacco leaves with calcium hydroxide derived from burnt shells to enhance the effects.
  • In Chinese cuisine, for making century eggs
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  • In the petrochemical industry for manufacturing solid oil of various marks
  • In the manufacture of brake pads
  • In the manufacture of ebonite
  • For preparation of dry mixes for painting and decorating
  • In manufacturing mixes for pesticides
  • In manufacturing the trademarked compound "Polikar", an antifungal and antimicrobial preservative for vegetables in storage
• In dentistry, it is used as dressing in paste form used for antimicrobial effect during a dental root canal procedure. Calcium hydroxide is known to have a strong antimicrobial effect and is a bone-regeneration stimulant.^[2]
• It has been proposed to add it to sea water in great quantities to reduce atmospheric CO₂ and fight the greenhouse effect[1]. However, since the production of calcium oxide (the main starting material of calcium hydroxide) involves calcination of limestone, which involves great deal of heat, it would be not very productive if fossil fuel were used in the production process.
• In the production of metals, lime is injected into the waste gas stream to neutralize acids, such as fluorides and chlorides prior to being released to atmosphere.
• Used in relaxers for permanently straightening very curly hair.