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Cross-market term

Lime binders

A binder made by burning limestone. It divides into non-hydraulic lime, which sets by absorbing carbon dioxide from the air, and hydraulic lime, which sets by reacting with water like a weak cement — two different materials under one word.
  • 4Markets
  • NoSame thing everywhere
  • 3Calculators

What it is called, by market

One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.

  • United Kingdom

    Same word, different thing

    lime

    also lime putty, NHL, hydraulic lime, hot lime, lime mortar

    NHL 2, 3.5 and 5 are hydraulic and set under water; lime PUTTY is non-hydraulic and sets by carbonation over months. The word alone does not say which, and they are not substitutes.

  • Australia

    Close, not identical

    lime

    also builders lime, hydrated lime, lime putty

    Builders lime normally means bagged hydrated non-hydraulic lime used as a plasticiser in cement mortar, rather than as a binder in its own right.

  • United Statesyours

    Same word, different thing

    lime

    also hydrated lime, Type S lime, Type N lime, NHL

    TYPE S and TYPE N here classify hydrated lime by its hydration, and collide directly with mortar Types S and N, which are strength designations for the finished mortar. Same letters, different property.

  • Canada

    Same word, different thing

    lime

    also hydrated lime, Type S lime, mason's lime

    As the United States, with the same Type S collision between lime classification and mortar strength designation.

The governing standard, by market

  • United Kingdom

    BS EN 459-1

    Building lime: definitions, specification and conformity criteria, including the NHL 2, 3.5 and 5 classification.

  • United States

    ASTM C207 / ASTM C1489

    Hydrated lime for masonry purposes including Types N and S, and lime putty for structural purposes.

Calculators for this

Each works in either measurement system, and the terminology on the page follows whichever market you have selected.

Soil Stabilization Lime Content Calculator →Thinset & Tile Adhesive Calculator →Manufactured Stone Veneer Mortar Coverage Calculator →

Frequently asked questions

What is the difference between hydraulic and non-hydraulic lime?
How it sets, and it changes everything about how the work is programmed. NON-HYDRAULIC lime — lime putty, sometimes called fat or air lime — sets by absorbing carbon dioxide from the air, a process that starts at the surface and works inward over months and years. It cannot set under water, it cannot set in a sealed void, and it must be protected from frost and from drying too fast for a long time after it is applied. HYDRAULIC lime contains clay impurities that give it cementitious compounds, so it sets by reacting with water like a weak cement, in days rather than months, and will set under water. NHL 2 is the weakest and most permeable, NHL 5 the strongest and closest to cement. Specifying NHL 5 where NHL 2 belongs is the same category of error as specifying cement on a soft wall, just less extreme.
Why does an old building need lime rather than cement?
Because of what the wall does with water, and because of what happens at the joint. A solid wall built with soft brick or stone and lime mortar handles rain by absorbing it and then releasing it, and the JOINTS are the main route out — lime is more permeable than the units, so the wall breathes through the mortar and the units stay relatively dry. Cement pointing reverses that: it is less permeable than the units, so the water leaves through the brick or stone face instead, carrying salts with it and freezing in it. The face then spalls. The second reason is movement: an old wall flexes, and lime accommodates that by microcracking and partly re-healing, where cement cracks once and stays cracked, usually taking the unit with it. Both effects take years, which is why the damage from a cement repair is normally attributed to something else.
What does Type S mean — is it the lime or the mortar?
Both, and they are unrelated properties, which is a genuine hazard in American specifications. ASTM C207 classifies hydrated LIME as Type N or Type S, where S means special hydrate with tighter limits on unhydrated oxides and on plasticity — it is about how the lime behaves in the mix. ASTM C270 classifies MORTAR as Types M, S, N, O and K in descending order of compressive strength, and Type S mortar is a strength designation containing cement, lime and sand. So a specification saying Type S might be naming the lime or naming the mortar, and the two have no connection: Type S lime appears in Type N mortar routinely. The only safe reading is to check which standard is cited, and a specification that cites neither has not specified anything.