FAQs

Terminology & Specifications

Q:  What is lime?  What are the differences between quicklime and hydrated lime, high calcium lime, and dolomitic lime?

A:  Although “lime” is sometimes used as a generic term for various materials, it should properly be used only to refer to the manufactured products quicklime and hydrated lime (click here for a short description on how lime is produced). Limestone, which is the feedstock for lime manufacturing, is not itself lime, although confusion is sometimes caused by references to limestone as “agricultural lime” or “aglime.”

Quicklime, the product of calcination of limestone (calcium carbonate and magnesium carbonate), consists of the oxides of calcium and magnesium and, in the United States, it is available in three forms:

• High calcium quicklime -- derived from limestone containing 0 to 5 percent magnesium carbonate.
• Magnesian quicklime -- derived from limestone containing 5 to 35 percent magnesium carbonate.
• Dolomitic quicklime -- derived from limestone containing 35 to 46 percent magnesium carbonate.

Hydrated lime is a dry powder manufactured by mixing quicklime with water, thereby converting the oxides to hydroxides.  Depending upon the type of quicklime used and the hydrating conditions employed, the amount of water in chemical combination varies, as follows:

• High calcium hydrated lime -- high calcium quicklime produces a hydrated lime containing generally 72 to 74 percent calcium oxide and 23 to 24 percent chemically combined water.
• Dolomitic hydrated lime (normal) -- under atmospheric hydrating conditions only the calcium oxide fraction of dolomitic quicklime hydrates, producing a hydrated lime of the following chemical composition:  46 to 48 percent calcium oxide, 33 to 34 percent magnesium oxide, and 15 to 17 percent chemically combined water.
• Dolomitic hydrated lime (pressure) -- this lime is produced from dolomitic quicklime under pressure, which results in hydrating all of the magnesium oxide as well as all of the calcium oxide, producing the following chemical composition:  40 to 42 percent calcium oxide, 29 to 30 percent magnesium oxide, and 25 to 27 percent chemically combined water.

Q:  What are the physical forms of lime?

A:  Quicklime is commercially available in a number of sizes (the following definitions are derived from ASTM Standard C51):

• Large lump lime -- a maximum of eight inches in diameter.
• Crushed or pebble lime -- ranging from about ¼ to 2½ inches.
• Ground lime -- ¼ inches and smaller.
• Pulverized lime -- a typical size is substantially all passing a No. 20 sieve.
• Pelletized lime – one-inch sized pellets or briquettes, molded from fines.

Hydrated lime is available only as a fine powder or a slurry.  Normal grades of hydrated lime suitable for most chemical purposes will have 85 percent or more passing a 200-mesh sieve, while for special applications, hydrated lime may be obtained as fine as 99.5 percent passing a 325-mesh sieve

Q:  What are the differences between Type N, NA, S, & SA hydrated lime used for mortar and other building applications?

A:  A short fact sheet on hydrated lime for masonry purposes is available.  Hydrated limes used in building applications are divided into four types, as described in ASTM Standard Specification C207 (Hydrated Lime for Masonry Purposes):

• Type N – normal hydrated lime
• Type NA – normal air-entraining hydrated lime
• Type S – special hydrated lime
• Type SA – special air-entraining hydrated lime

Types S and SA are differentiated from Types N and NA principally by the unhydrated oxide content and their water retention value.  Type S must meet a water retention value of 85%, while Type N hydrate lime must have a water retention value of 75%.  No distinction is made based on the nature and source of limestone.  The maximum air content of cement-lime mortar made with Types NA and SA is 14%; with Types N or S lime, 7%.

Q:  Is aglime the same as lime?

A:  No. The term agricultural lime, or "aglime," usually refers to crushed limestone.  Limestone (calcium carbonate) is not the same as hydrated lime (calcium hydroxide).

Q:  Do you have a listing of the specifications for lime in various industrial uses?

A:  A complete list of standards is available at Lime Standards.

Q:  What procedures should I use to test lime?

A:  ASTM has Standard Methods for testing chemical (C25) and physical (C110) properties.  These standards can be purchased directly from ASTM at www.astm.org.

Handling & Transport

Q:  Do you have technical advice on how to design lime storage and conveyance systems?  What type of lime handling equipment should I buy?

A:  NLA’s "Lime Handling, Application & Storage" publication includes information on the handling and storage of lime, equipment for application of lime, lime slaking and slurry handling, and factors affecting the selection of lime.  Contact your lime supplier for more specific technical assistance and advice on equipment vendors.

Q:  Are there any handling or safety precautions that workers should follow?

A:  Please see "Fact Sheet: Lime Safety Precautions."

Q:  What regulations apply to transporting lime?

A:  Lime is generally not regulated as a hazardous chemical when transported.  The one exception is airborne shipments of quicklime.  A fact sheet on shipment of quicklime by air is available.

Soil-Related & Agricultural Applications

Q:  How much lime should I use to stabilize soils?

A:  A fact sheet on soil stabilization is available under Technical Information.  NLA offers several free downloads on soil stabilization with lime.

Q:  Can’t lime be used to dry up mud — for short-term soil modification to expedite construction?

A:  Yes, a fact sheet on using lime to dry up mud called “Lime Dries Up Mud” is available.

Q:  How much lime should I use on my garden?

A:  Hydrated lime can be used to raise the pH of acidic soils.  This is also referred to as soil "sweetening."  Hydrated lime is available from garden centers and should be applied in the amounts and using the procedures recommended on the packaging.

Lime Suppliers

Q:  Where can I obtain lime?

A:  A list of U.S. and Canadian lime suppliers by state/province is available under Find a Lime Plant.

Q:  Where can I obtain food grade lime?

A:  W e are aware of one company that makes food grade lime:  Mississippi Lime (www.mississippilime.com).

Q:  Where can I obtain lime for masonry and other building applications?

A:  Building lime can be obtained from Carmeuse, Graymont, Lhoist North America, and Mississippi Lime.

Other Topics

Q:  How do I use lime to make whitewash?

A:  NLA has no current publications that address whitewash.  Other references include:

• P. Mold & R. Godbey. "Limewash - Compatible Coverings for Masonry & Stucco." 2005, International Building Lime Symposium Proceedings (ISBN 0-9767621-0-2).
• R. Bennett. "The Use of Limewash as a Decorative and Protective Coating." The Building Conservation Directory, 1997, pp. 136-137.
• [British] Quarry Products Association (formerly the British Quarry and Slag Federation). "Lime in Building." 1974.

If you have a question concerning lime, please email us or contact us at (703) 243-5463 ext. 226.