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    A Comparison of Critical Properties of Magnesium Oxysulfate and Magnesium Oxychloride Cements as Used in Sprayed Fire Resistive Coatings

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    Magnesium oxysulfate cements although not as strong as magnesium oxychloride cements are better suited for fire resistive uses. Magnesium oxysulfate cements start to decompose at temperatures more than two times higher than magnesium oxychloride cements decompose giving longer fire protection. Their products of decomposition at elevated temperatures are less noxious (sulfur dioxide) than those of oxychloride (hydrochloric acid) and less corrosive.

    Weather conditions (humidity, temperature, and wind) during application are not as critical with oxysulfates as with oxychloride, which may partially form unstable magnesium hydroxide instead of magnesium oxychloride. Commonly known as “burnout” or “dry set,” this unwanted reaction can be the cause of loss of bond, cracking, loss of volumetric stability, poor physical properties, and corrosion. Since fire resistive coatings are generally light in density, they are not expected to be as strong as flooring products where the oxychlorides are normally used and are superior. For the intended use as fire resistive and insulative coatings, when those properties are compared, magnesium oxysulfate cements are preferred.


    coatings, magnesium oxysulfate, magnesium oxychloride, fire resistive, volumetric stability, corrosion

    Author Information:

    Herrera, ME
    Vice-president, Research and Development, American Energy Products Corp., Walnut, Calif.

    Committee/Subcommittee: E06.21

    DOI: 10.1520/STP31895S