National Lime Association

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

A:   Lime is a generic term, but by strict definition it embraces only the manufactured forms of lime—quicklime and hydrated lime. It does not include limestone, which is the feedstock for lime manufacturing (click here for a short description on how lime is produced).

Quicklime, the product of calcination of limestone, 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 treating quicklime with sufficient water to satisfy its chemical affinity for 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 about physical specifications for lime?

A: 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.

Quicklime, however, 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 2 ½ 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.

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 under Technical Information.

Hydrated limes used in building applications are divided into four types, as described in ASTM Standard Specification C 207 (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 their ability to develop high early plasticity, higher water retentivity, and by their limitation on unhydrated oxide content. 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:   The term agricultural lime, or "aglime," usually refers to 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:   There is an ASTM standard, C911, for lime used in chemical (and industrial) uses. Uses addressed include water softening, other water treatment, hypochlorite bleach, silica brick, calcium silicate products, industrial waste treatment, sulfite pulp, and carbide. The standard can be purchased directly from ASTM at www.astm.org.
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.
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:  How does the National Fire Protection Association (NFPA) rate lime?

A:   The NFPA has a 0 to 4 rating system for potential hazards that may be encountered during fires and other emergency response situations. NFPA classifies calcium oxide (quicklime) as a serious health hazard (category 3) because of its potential to cause irreversible injury to the eye. The NFPA classifies quicklime as a non-flammable material (category 0), and slightly reactive with water (category 1). More details appear in NPFA’s Hazardous Chemicals Data Handbook (NFPA 49), see www.nfpa.org . The NFPA Handbook does not include ratings for other forms of lime or lime by-products, but by NFPA’s criteria, hydrated lime should be a category 1 health hazard and category 0 for both flammability and instability hazards.

For safety precautions, the MSDS for the specific product should be reviewed.
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 under Technical Information.
Q:  How much lime should I use to stabilize clay soils to generate long-term strength gain?

A:   A fact sheet on soil stabilization is available under Technical Information.

There is an ASTM test method to approximate the amount of lime needed to stabilize soils, D 6276.  (This procedure is also called the Eades and Grim test.)  The standard can be purchased directly from ASTM, www.astm.org .

However, to be confident that a stabilized soil can provide structural strength, more rigorous testing is required.  The National Lime Association has proposed a testing protocol in a report entitled "Evaluation of Structural Properties of Lime Stabilized Soils and Aggregates, Volume 3: Mixture Design and Testing Protocol for Lime Stabilized Soils."  March 2000.  This report is available under Technical Information.

 
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 is available under Technical Information.
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.
Q:  Where can I obtain lime?

A:  A list of U.S. and Canadian lime suppliers by state/province is available under the Lime Supplier Portal. Suppliers can also be identified from the map under the Members area.

Q:  Where can I obtain food grade lime?
A:   We 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:   See the contact list at the end of the fact sheet on hydrated lime for masonry purposes, which is available under Technical Information.
Q:  What is the current price for lime?

A:   See the U.S. Geological Survey’s annual Minerals Yearbook on lime [or the Canadian annual Minerals Yearbook].

Q:  How do I use lime to make whitewash?

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

Q:  Can I use lime to kill darkling beetles, sow bugs, other insects—or as a disinfectant?
A:   Although lime is not a registered pesticide, it has been endorsed by EPA as a means to control pathogens in sewage sludge (biosolids). It controls the environment required for bacterial growth.
 
If you have a question concerning lime, please e-mail us or contact us at (703) 243-5463.
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