ASTM C1922
Informative Article on ASTM C1922 - Water Retention Test for Mortar and Plaster
Introduction
The ASTM C1922 test method is a standardized procedure developed to measure the water retention capacity of mortars and plasters. This test is crucial for evaluating the performance of these materials in various construction applications, particularly how they interact with different substrates.
Summary of Test Method
The test involves mixing mortar or plaster with a specified amount of water and then applying it to a chosen substrate within a test frame. The process entails:
Preparation: Mortar or plaster is mixed as per manufacturer’s recommendation.
Application: The mix is applied on a substrate, chosen based on intended use, within a specified area in the test frame.
Waiting Period: After a 5-minute standing period, the material is removed.
Measurement: The substrate, now with absorbed water, is immediately weighed.
Calculation: Water retention is calculated as a percentage of water transferred from the mortar to the substrate.
Significance and Use
Comparative Analysis: This method is vital for comparing how different mortars or plasters retain water when applied to various substrates.
Application-Specific Insights: It helps in understanding the water retention characteristics in relation to specific substrates.
Limitations: The test does not account for environmental factors and may not reflect actual field conditions.
Interferences
Substrate Absorption: The test results are influenced by the water absorption capacity of the substrate used. Therefore, the choice of substrate should be reported alongside the results.
Apparatus and Materials
Straightedge: A steel straightedge for even application.
Mixing Apparatus: As per Practice C305.
Balance: Accurate to 0.1% of the test load.
Test Apparatus: Includes a nonabsorbent frame, plate, and filter paper.
Timer: For precise time measurement.
Tamper: Made of nonabsorptive, nonabrasive material.
Mortar Assembly: Consisting of the test apparatus components, substrate, and mortar.
Materials
Mortar/Plaster Composition: As per the specification of the material.
Nonwoven Filter: A specific grade of nonwoven filter paper.
Substrates: Various substrates like concrete, tile, gypsum board, etc., can be used based on the application of the mortar.
Detailed Test Method
Mixture Preparation: The mortar or plaster is mixed according to specific guidelines.
Apparatus Assembly: Set up the test apparatus with the chosen substrate.
Application: Apply the mortar or plaster within the test frame on the substrate.
Timing: Allow the setup to stand for 5 minutes.
Weighing: Post the standing period, weigh the substrate with the absorbed water.
Calculation: Determine the water retention percentage by comparing the weight before and after the test.
Repetition for Comparison: The test can be repeated with different substrates or mortar types for comparative analysis.
Conclusion
ASTM C1922 offers a standardized way to assess the water retention properties of mortars and plasters. While providing valuable insights for material selection in construction, it is important to note its limitations regarding environmental conditions and actual field application. Understanding these nuances is critical for architects, builders, and material scientists in making informed decisions about material usage in construction projects.