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Graymont products for this industry :
Dolomitic Hydrate Type N
Dolomitic Hydrate Type S
Dolomitic Hydrate Type SA
Mason's Pre-Blend Type N/Type S
Niagara Lime Putty

Technical Papers & Links :
History of Lime in Mortar
Mortar Mix Designs
Benefits of Cement-Lime Mortar
What is Mason's Lime?
Benefits of Type S Hydrated Lime
Mixing Methods
Masonry Links

Mortar Mix Designs

How Is Lime Specified Into Mortars?

Portland cement-lime mortars are specified in two steps. First, the mortar type must be determined based on the strength required for the application. Secondly, a choice must be made between specifying proportions or properties listed in ASTM C270.

The ASTM Standard C270 (Mortar for Unit Masonry) provides the basis for specifying cement-lime mortars. This specification provides the basis for five different mortar types (Type K is listed in section X3 of the appendix) depending on the strength of mortar needed for an application. The names for these mortar types, developed in 1954, were based on alternating letters of the phrase "MASON WORK". Type M mortar has the highest strength. Type K mortar has the lowest compressive strength.

The Appendix of ASTM C270 provides a reference to which mortar type should be used in some general applications. A version of this list is shown in Table 1.

TABLE 1a
Mortar Type
Location
Building Segment
Recommended
Alternative
Exterior, above grade
Load-bearing wall
Non-load bearing wall
Parapet wall
N
Ob
N
S or M
N or S
S
Exterior, at or below grade
Foundation wall, retaining wall, manholes, sewers, pavements, walks, and patios
Sc
M or Nc
Interior
Load-bearing wall
N
S or M
Non-bearing partitions
O
N

a This table does not provide for many specialized mortar uses, such as chimney, reinforced masonry, and acid resistant mortars.

b Type O mortar is recommended for use where the masonry is unlikely to be frozen when saturated, or unlikely to be subjected to high winds or other significant lateral loads. Type N or S mortar should be used in other cases.

c Masonry exposed to weather in a nominally horizontal surface is extremely vulnerable to weathering. Mortar for such masonry should be selected with due caution.

The materials which could be used in a cement-lime mortar are defined in ASTM C270 (Mortar for Unit Masonry).

  • Portland Cement - Types I, IA, II, IIA, III or IIIA of ASTM Specification C150 or

  • Blended Hydraulic Cement - Types IS, IS-A, IP, IP-A, I(PM), I(PM)-A of ASTM Specification C595/595M

  • Quicklime - ASTM Specification C5

  • Lime Putty - ASTM Specification C1489

  • Hydrated Lime - Type S or SA of ASTM Specification C207. Note: If a Type SA Hydrated Lime product is used, air entrained portland cement products should not be used.
    TABLE 2
    Mortar Component
    Bulk Density (lbs/ft3)
    Portland Cement
    94
    Hydrated Lime
    40
    Mason's Sand, damp & loose
    80 (dry)

  • Aggregates - ASTM specification C144
ASTM Standard C270 provides both a proportion specification and a property specification for each mortar type.

The proportion specification provides a recipe based on volume. For cement-lime mortars, the proportion specification will indicate the volume of portland cement followed by the volume of hydrated lime and finally the volume of sand. For example, a 1::4 mix contains 1 cubic foot of portland cement plus of a cubic foot of hydrated lime and 4 cubic feet of sand. For the purposes of determining volumes, ASTM C270 provides typical bulk densities for portland cement, hydrated lime and sand. These densities are shown in Table 2. Table 3 details the recipes required for each mortar type specified by proportion. Type N hydrated lime products must be laboratory tested to insure that they meet the property specification for the applicable mortar type in order to be acceptable for the proportion specifications.


TABLE 3 - ASTM C270 Proportion Specification
Mortar Type
Proportions by volume
(cementitious materials)
Aggregate Ratio - Measured in damp, loose conditions
Cement
Lime
M
1
Not less than 2 and not more than 3 times the sum of the separate volumes of cementitious materials
S
1
Over to
N
1
Over to 1
O
1
Over 1 to 2

The property specification requires that the mortar exhibit certain characteristics when tested under laboratory conditions. As seen in Table 4, compressive strength, water retention and air content tests are required to be performed on the mortar mixed in the laboratory. Since jobsite water additions may not be the same as those in the laboratory, the properties of field mixed mortar cannot be compared to the property requirements of ASTM C270.

Portland cement-lime mortars should be specified by either the property or the proportion specification but not both. When neither the proportion or property specifications are specified, the proportion specifications govern.

TABLE 4 - ASTM C270 Property SpecificationA
Mortar Type
Average Compressive Strength at 28 Days (min. psi)
Water Retention
(min. %)
Air Content
max. %
Aggregate Ratio
M
2,500
75
12
Not less than 2 and not more than 3 times the sum of the separate volumes of cementitious materials
S
1,800
75
12
N
750
75
14B
O
350
75
14B
A Laboratory Prepared Mortar Only

B When structural reinforcement is incorporated into cement-lime mortar, the maximum air content shall be 12%

For the complete ASTM C270 document, visit the website www.astm.org.

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