Lime

Summary

Lime is calcium oxide (quicklime) made by heating limestone, and calcium hydroxide (hydrated or slaked lime) formed by adding water to it. It is the binder in traditional plaster, mortar, and stucco, and it hardens by absorbing carbon dioxide unless it is hydraulic.

Cols

Image

Quicklime: calcium oxide (CaO)
Hydrated (slaked) lime: calcium hydroxide, Ca(OH)2
Lime putty: made by wet slaking with a slight excess of water
Natural hydraulic lime (NHL): from limestone that naturally contains some clay
Dolomitic lime: 35 to 46 percent magnesium carbonate (ASTM C59)
Selenitic lime: about 5 percent added gypsum plaster

History and demand

First uses in construction

Romans used two types of lime mortar to make Roman concrete

Sourcing

2025 world lime production was about 420 million tons (estimate), with the United States about 15 million tons; China produced about 310 million tons in the 2025 edition (USGS)

Composition and production

Raw materials

Limestone with 80 percent or more calcium or magnesium carbonate; pure lime may contain up to 5 percent other ingredients

Manufacturing process

Limestone is calcined above 900°C (1,650°F) in a kiln to make quicklime
Dry slaking uses just enough water to keep the quicklime a powder; wet slaking makes putty

Grades and types

Feebly hydraulic: 5 to 10 percent clay; slakes in minutes; sets in about three weeks
Moderately hydraulic: 11 to 20 percent clay; slakes in 1 to 2 hours; sets in about one week
Eminently hydraulic: 21 to 30 percent clay; slakes very slowly; sets in about one day
Semi-hydraulic: minimum 6 percent soluble silica
Magnesium lime: 5 to 35 percent magnesium carbonate (ASTM C59)

Properties

Durability

Slaked lime hardens by reacting with carbon dioxide to form calcium carbonate
Pure lime is not hydraulic and will not set under water

Standards

Material specifications

ASTM C207: hydrated lime for masonry
ASTM C59: quicklime and magnesium lime composition

Uses in buildings

Building elements

Pros and cons

Pros

Hardens by carbonation without cement
Hydraulic grades set in days
Long historical record in plaster and mortar

Cons

Pure lime does not set under water
Feebly hydraulic limes take about three weeks to set

Manufacturing and cost

Main manufacturers and suppliers

Trade association: National Lime Association.

Sources

Wikipedia: Lime (material), https://en.wikipedia.org/wiki/Lime_(material)
Wikimedia Commons: Agricultural lime in field. Lime pile.jpg, photo by Slknight (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:Agricultural_lime_in_field._Lime_pile.jpg
USGS: Mineral Commodity Summaries 2026, lime, https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-lime.pdf