July 2011 eNews
Pre-blended Portland Cement Plaster Basecoats
Ben Garcia, Expo Stucco Products
Construction specifications setting forth the minimum requirements for plastering work must be closely adhered to, whether stated in industry-wide standards and guide specifications or in local building codes. These written specifications establish acceptance requirements for the quality of materials and workmanship.
Portland cement plaster is a combination of cementitious material, fine aggregate, lime and water. When properly proportioned, these materials will provide a hard, durable plaster surface that provides reasonable resistance to weather and cracking.
A major concern voiced by many experts in the plastering field is the variation and lack of control in job site mixing of sand and cement used in portland cement plaster for the scratch and brown coats. Sand added in excess of recommended parameters can seriously affect the integrity on the entire wall assembly.
Another growing issue is the use of sand piles on job sites. At times restricted sites and multi-story projects cannot accommodate the space required for these large mounds of sand. Some organizations restrict sand piles over concerns of airborne dust and run off in the case of storms.
The high cost of on-site injuries is a challenge. Health and safety concerns have increased over the shoveling and heavy lifting associated with field mixing. An average of 383 injuries occur per every 10,000 workers per year.
(Source: Nonfatal Occupational Injuries and Illnesses Requiring Days Away From Work, 2008, Bureau of Labor Statistics, 11/24/09, http://www.bls.gov/news.release/osh2.nr0.htm)
Preblended basecoat mixes were developed to solve these challenges. Factory blended plaster mixes are specifically designed to conform to ASTM and IBC requirements for scratch and brown plaster applications. What's unique is that the mixing happens at the factory, not on the jobsite.
These mixes are complete requiring only the addition of water. This control of the mix ratio at the factory eliminates the inconsistency associated with job-site mixes. This provides a consistent mix from batch-to-batch which aids in producing a uniform, durable basecoat.
Factory blended portland cement plaster has excellent pumping and troweling properties for the contractor, while providing the building owner with a durable plaster.
There is no sand to shovel. All a contractor needs is to start the mixer and add water, saving time, space and possibly money.
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