There are several types of hydrated lime products defined for masonry applications in the ASTM standard C207 (Standard Specification for Hydrated Lime for Masonry Purposes).
Type N, or normal hydrated lime, products are only partially hydrated and/or have poor workability. Additional additives and/or long soak periods are required for these products to perform effectively in masonry applications. At least a 24 hour soak period is required before Type N dolomitic hydrate can be used acceptably for masonry applications. High calcium hydrated lime products normally are classified as Type N hydrates due to their poor water retention. ASTM C270 (Mortar for Unit Masonry) specification states that if a Portland Cement / Lime blend contains Type N hydrate, the blender must show through performance testing that the Type N product is not detrimental to the soundness of the mortar. Type N hydrated lime products contain a maximum of 7% air.
Type NA, or Normal Air-Entraining lime, is a type N hydrated lime containing an air-entraining additive. These products must entrain between 7% and 14% air when mixed with cement and sand in mortars. If mixed in a Type M mortar or utilized in a structural reinforcement application, the air content of the mortar cannot exceed 12%.
Type S, or Special hydrated lime products, are a combination of calcium and magnesium hydroxides. In building applications, Type S dolomitic hydrated lime products have high hydration levels and controlled plasticity (water retention). This allows for minimal soak periods prior to application. These products cannot entrain over 7% air. Due to the ease of mixing, high bond strength and high plasticity level of these products, Type S hydrated lime is used in most masonry applications where cement lime mortars are used in the United States. (Why Type S Lime is the best lime in the joint?)
Type SA, or Special Air-Entraining lime, is a type S hydrated lime containing an air-entraining additive. These products must entrain between 7% and 14% air when mixed with cement and sand in mortars. If mixed in a Type M mortar or utilized in a structural reinforcement application, the air content of the mortar cannot exceed 12%.
The required characteristics of Type N and Type S hydrated lime products in ASTM C270 (Hydrated Lime for Masonry Purposes) are seen in the following table:
|Parameter||Type N||Type NA||Type S||Type SA|
|Calcium & Magnesium Oxides (nonvolatile basis), min. %||95%||95%||95%||95%|
|Carbon Dioxide (as-received basis), max. %||5%||5%||5%||5%|
|Unhydrated Oxides (as-received basis), max. %||8%||8%|
|Plus 30 Mesh Residue, max. % on, (or no pops or pits)||0.5%||0.5%||0.5%||0.5%|
|Plasticity (Emley Units), min.||200||200|
|Air Content - Minimum (%)||7%||7%||94|
|Air Content - Maximum (%)||7%||12-14%||7%||12-14%|
|Water Retention (%) min.||75%||75%||85%||85%|
For the sizing analysis, if the sample retains over 0.5% 30 mesh residue, the product is acceptable if it passes the pop plate test with no pops or pits. All test procedures in these standards are based on methods in ASTM C25 (Chemical Analysis of Limestone, Quicklime, and Hydrated Lime) and ASTM C110 (Physical Testing of Quicklime, Hydrated Lime, and Limestone).
NOTE: Air entrained lime products should not be used in mix designs with air entrained cement products.