Masonry Magazine October 2000 Page. 22
Table 3.
GUIDE FOR SELECTION OF MASONRY MORTARS*
Mortar type
Location
Building segment
Recommended
Alternative
Exterior, above grade
Load-bearing walls
N
S or M
Non-load-bearing walls
0**
N or S
Parapet walls
N
S
Exterior, at or below grade
Foundation walls, retaining walls, manholes
St
Mor Nt
sewers, pavements, walks and patios
Interor
Load-bearing walls
N
S or M
Non-load-bearing partitions
0
N
Adapted from ASTM C 270. This table does not provide for specialized mortar uses, such as chimney, reinforced masonry, and acid-resistant mortars.
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.
↑ Masonry exposed to weather in a nominally horizontal surface is extremely vulnerable to weathering. Mortar for such masonry should be selected with due caution.
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cement mortars for structural masonry in high seismic performance categories.
In addition to structural requirements, the properties of units and expected environmental conditions should be considered. For example, more workable, water retentive mortars are better suited for use with high absorption units than a high-strength, low water retentive mortar. Conversely, with a low absorption unit under cold weather construction conditions, a less water retentive, faster setting mortar is desirable.
Special attention to mortar selection should be given when severe exposure conditions are expected. Type O mortar should not be used in saturated freezing conditions. For severe frost action such as horizontal paving applications, Type M mortar should be considered. Air-entrainment should be used to improve freeze-thaw durability.
SUMMARY
As can be seen from this discussion, selection of mortar though appearing to be a simple matter, involves some rather complex issues related to materials, design, and construction. Ideally, input from the engineer, architect, mason contractor, and owner would be considered along with influencing factors such as weather conditions to optimize the selection of mortar on a project. In reality, the design-bid-build process used for most masonry construction precludes that level of interaction. However, as specifiers and contractors better understand the influence of mortar selection on the construction process and the masonry product, they can become more confident of making the right choices.
John Melander is the Director of Product Standards and Technology of the Portland Cement Association