Masonry Magazine June 2002 Page. 31
AMERICAN LIMESTONE COMPANY
AMERICAN LIMESTONE COMPANY
Mortar and Grout
THE MOST IMPORTANT materials that need special attention are the mortar and grout. Mortar temperatures and properties, masonry unit temperatures and properties, wind velocity and relative humidity can all have adverse effects on the performance of mortar in masonry.
As the temperature of the mortar increases, many physical properties change. For example, workability is reduced and more water must be added to maintain a proper workability. As the temperature increases, both initial and final set occur earlier. Also, depending on the surface characteristics, temperature and moisture content of the masonry units, moisture kiss from the mortar due to suction takes place much more rapidly.
Rapid water loss due to evaporation and suction reduces the amount of water available for hydration of the cement. Since hydration of cement is necessary for normal strength development of mortar, a reduction of strength development may occur under rapid drying conditions. Evaporation removes moisture more rapidly from the surface of mortar joints resulting in weaker mortar on the surface.
Covering the walls immediately after construction will effectively slow the rate of water loss from the masonry while the application of a fog spray during the first 72 hours can reduce the effects of hot, dry and windy weather. Strength development in masonry subjected to early dry-out often can be reactivated by spraying the masonry with water.
Grout also sets quicker in higher ambient temperatures. However, the effects are primarily influenced by the temperature of the wall into which the grout is placed. Though this influence disturbs placement procedures, it has no adverse effect on final strength.
Clay and Concrete Masonry Units
WHEN CONSIDERING the influence of masonry units on construction during hot weather, one should recognize that the absorption of the units might vary depending on their exposure at the site. Units heated and dried by the sun will absorb more water from the mortar and grout than units kept shaded.
High absorption units can contribute to rapid dry-out of mortars in hot weather. Wetting of high absorption fired clay units prior to use will reduce this tendency to dry out the mortar. Concrete masonry units should not be wetted before use, but concrete masonry can be covered with wet burlap or water sprayed after walls are constructed to assure adequate curing moisture. Though not recommended, a light mist can also be applied to the units prior to installation.
Planning and Construction
PLANNING, PREPARATION and procedures for hot weather masonry construction should focus on assuring that mortar remains workable from the time of mixing until placement of units and that sufficient moisture remains in the masonry units to The Voice of the Mason Contractor
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Design by Drafting and Design Solutions Nov 2001
June 2002
Masonry 29