Masonry Magazine March 1978 Page. 14
Note 1. The weights per cubic foot (kg/m³) of the materials are considered to be as follows:
Material
Portland cement
Hydrated lime
Sand, damp and loose
Weight, Ib per cu ft (kg/m³)
94 (1504)
40 (640)
80 lb (1280) of dry sand
4.2 Mixing Mortars. All cementitious materials and aggregate shall be mixed for at least 3 min and not more than 5 min in a mechanical batch mixer, with the maximum amount of water to produce a workable consistency.
4.3 Retempering. Mortars that have stiffened because of evaporation of water from the mortar shall be retempered by adding water as frequently as needed to restore the required consistency. Mortars shall be used and placed in final position within 2½ hr after initial mixing.
5. PROPORTIONS
5.1 The mortar shall be proportioned within the limits given in Table 1 for each type specified.
TABLE 1
Mortar Proportions by Volume
Parts by
Volume of
Mortar Portland
Type Cement
MSNO
1
1
1
1
Parts by
Volume of
Hydrated
Lime
3%
1½
1
2
Sand, Measured in a
Damp, Loose Condition
Not less than 2% and
not more than 3 times
the sum of the volumes
of cement and lime used.
6. PHYSICAL PROPERTIES
6.1 Laboratory Prepared Mortar. Laboratory mortar samples prepared and tested in accordance with Section 7 shall conform to the physical requirements for each type specified as prescribed in Table 2.
6.2 Construction Mortar. Construction mortar meeting the requirements of Sections 3, 4 and 5, and measured and mixed under supervision at the construction site, shall not be required to meet the compressive strength requirements given in Table 2 for the type specified (Note 2).
Note 2. Experience has indicated that portland cement-hydrated lime mortars of the types specified here, the materials of which conform to the requirements of Section 3, and whose proportions are accurately measured and mixed to flows suitable for use in laying masonry units, may not conform to the compressive strength requirements in Table 2, because of the higher water content and the variable curing conditions to which they are normally subject to at the job site.
7. METHODS OF TESTING
7.1 Compressive strength and water retention of the mortar shall be determined in accordance with ASTM Standard Specification C 91, with the following exceptions:
7.1.1 Mortar samples mixed in the laboratory shall be made using the same proportions and the same ingredients that will be used for the mortar in the construction, but with a flow of 130 ± 5 percent.
7.1.2 Mortar cubes of Types N and O mortar prepared in the laboratory for compressive strength tests, when removed from the molds, shall be kept in a damp closet until tested.
7.2 The air content of the mortar shall be determined in accordance with ASTM Method C 231.
7.3 The efflorescence tendency of the mortar shall be determined, using the wick test described in Brick Institute of America Research Report No. 15, The Causes and Control of Efflorescence in Brickwork, Section 4.4, page 14.
8. COSTS OF TESTS
8.1 Unless otherwise specified, the costs of tests shall be borne as follows:
8.1.1 If the results of the tests of laboratory prepared mortar show that the mortar does not
TABLE 2
Physical Requirements of Laboratory Mixed Mortar
Compressive Strength¹
Mortar
Type
Minimum
7 days²
Minimum
28 days
Minimum
Water
Retention³
Maximum
Air
Content
Efflorescence
psi
(kgf/cm²)
psi
(kgf/cm²)
%
%
M
1600 (112)
2500
(175)
S
1100 (77)
1800
(126
N
450 (32)
750
(53)
70
12
None
0
200 (14)
350
(25)
¹Average of three 2-in. cubes.
²If the mortar fails to meet the 7-day compressive strength requirement, but meets the 28-day compressive strength requirement, it shall be acceptable.
³Flow after suction, percent of original flow.