Masonry Magazine January 1970 Page. 37
Accelerators and Coloring Agents
Accelerators are used to speed up the setting time of mortar. However, some materials should not be used as accelerators, which will result in excessively rapid setting of mortar (flash set).
Commercial products marketed as accelerators offer increased workability, faster gain in strength, and rapid set. Such products, composed mainly of calcium chloride, may be employed where experience or testing demonstrates that such use does not result in deleterious effects such as corrosion of imbedded metal, excessive volume change, variation in color, or efflorescence.
Coloring agents may contain dispersants which speed the distribution of color throughout the mortar mixture. The dispersing agents may have a retarding effect on the hydration of the portland cement. The result could be a slow set of the mortar and slow development of strength. Coloring agents should therefore not be used without prior testing or experience which shows acceptable effects.
Materials Storage
Masonry units and materials for mortar should be kept on a platform raised to prevent wetting from ground moisture. If not otherwise enclosed, the materials should be covered with tarpaulins, plastics sheets, or the like. Masonry sand which is delivered in bulk should be covered to prevent entrance of water from melting ice and snow. Careless storage of materials increases the cost of masonry construction since ice and snow must be removed and the masonry units thawed before used in construction.
Heating Materials
The most important consideration in heating concrete masonry materials is that sufficient heat be provided to assure hydration of the cement content in mortar. After combining all ingredients, the temperature of the mortar should be within a range of 70°F. and 120°F. Mortar temperatures in excess of 120°F. may cause excessively fast hardening with a resultant loss of compressive strength and bond strength. The mixing water is the most logical masonry material to be heated because of its high specific heat. In general the mixing water should not be heated above 160°F. to avoid false set. When heating of the mixing water alone is insufficient it will be necessary to heat the sand as well. Sand should not be heated to the point where decomposition or scorching can occur. When the outside temperature is below 20°F. the concrete masonry units should be heated to about 40°F., to prevent sudden cooling of the heated mortar as it comes in contact with the cold block.
Water may be heated by any of several methods. Any method which does not add deleterious matter to the water is acceptable. Coke burning salamanders, flame guns, and oil drums with fire underneath are commonly employed. Where steam is available rapid heating is accomplished by injecting steam into the water. When sand is heated, any means is satisfactory as
Fig. 1 Heating Concrete Masonry Units
Table 4. Construction Requirements
| Air Temperature (°F.) | CONSTRUCTION REQUIREMENTS |
|---|---|
| 40-32 | Heat mixing water or sand to minimum of 70°F. and maximum of 160°F. |
| 32-25 | Heat mixing water and sand to minimum of 70°F. and maximum of 160°F. |
| 25-20 | Heat mixing water and sand to minimum of 70°F. and maximum of 160°F. Utilize sources of heat on both sides of walls under construction. Employ windbreaks when wind is in excess of 15 mph. |
| 20 and Below | Heat mixing water and sand to minimum of 70°F. and maximum of 160°F. Provide enclosure and auxiliary heat to maintain air temperature above 32°F. Temperature of units when laid shall not be less than 20°F. |
Fig. 2 Temporary Enclosures During Construction
Fig. 3 Enclosure for Scaffold
Table 5. Protection Requirements
| Mean Daily Air Temperature (°F.) | PROTECTION REQUIREMENTS (completed masonry or sections not being worked on) |
|---|---|
| 40-32 | Protect masonry from rain or snow for 24 hours. |
| 32-25 | Completely cover masonry for 24 hours. |
| 25-20 | Completely cover masonry with insulating blankets for 24 hours. |
| 20 and Below | Maintain masonry temperature above 32°F. for 24 hours by enclosure and supplementary heat, by electric heating blankets. infrared heat lamps or other approved method. |