Concrete Floor Slab Design
As a testing agency, we make no claim to be structural or design engineers. However, we endeavor to stay abreast of guides and standards published by the American Society for Testing and Materials (ASTM), the Portland Cement Association (PCA) and the American Concrete Institute (ACI) as they relate to floor covering and concrete floor slab system design.
ACI has published a Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials, which also known by its alpha-numeric designation ACI 302.2R-06. The guide is intended to be an adjunct to ACI 302.1R-15 Guide for Concrete Floor and Slab Construction and ACI 360R Design of Slabs-on-Ground. As the title indicates, ACI 302.2R was produced as a guide to help the construction and design community understand factors related to: moisture in concrete, the process by which concrete dries, how moisture may move through concrete, how to test the dryness of concrete, moisture's affect on modern floor covering systems and the potential need to employ a "sealer" system.
In our opinion and experience, virtually every directly adhered floor covering system currently available is moisture-sensitive. We therefore believe that the information and recommendations contained in ACI 302.2R-06 should be employed in the design and placement of all indoor concrete floor slabs. Building Owners, developers and Architects will ultimately be the people who must ensure that a floor slab is designed to support the installation of floor coverings. Contractors must ensure that plans and specifications are followed, so that directly adhered floor coverings can successfully serve their purpose.
One of the issues addressed in ACI 302.2R is the requirement to install a sub-slab vapor retarder. As an agency that typically deals with moisture related floor covering system distress and/or failure, we would recommend that owners, developers and architects consider placing high quality sub-slab vapor retarders directly beneath the entire indoor footprint of any building that they are designing or having constructed. The minimum requirements for such a membrane are contained in ASTM E 1745. This standard classifies vapor retarders based on permeability, tensile strength and puncture resistance. A number of vapor retarder manufacturers offer products that dramatically exceed the standard values required by ASTM. In example, it is our opinion that construction specifications should require that a sub-slab vapor retarder have a permeability rating of 0.050 perms, or less, which exceeds the 0.10 requirement listed in ASTM E 1745. We further recommend that prospective tenants confirm the existence of a vapor retarder and request test result data or other information regarding the suitability of any potential lease space for the installation of floor coverings, prior to signing a lease. We are often called to buildings that were designed to be office/warehouse configurations, in which a vapor retarder was specified to be placed only under the area "pre-determined" to be utilized for office occupancy. When a tenant moves in and expands their office/lab/production space into areas that were intended for warehouse use, a moisture related floor covering system failure often follows. The cost of placing a vapor retarder beneath concrete is typically measured in pennies per square foot, anyone that has borne the cost of topically applied sealers knows that the cost of these systems is measured in dollars per square foot.
The American Concrete Institute's committee 302 has put a great deal of time and effort into the publication of guides that help deal with all aspects of concrete floor slab construction, not the least of which is the ability of a floor slab to support the installation of modern moisture-sensitive floor covering systems. We sincerely hope that the on-going educational efforts of various trade and professional organizations will eventually cause the design and construction communities across the country to recognize the relative ease with which most moisture related floor covering system failures can be prevented, through the implementation of standards and practices currently published by ASTM and ACI.
To purchase copies of the ACI guides referenced above simply click on the link below and go to the ACI "Bookstore and Publications" section.
Additional vapor retarder information and specifications can be found at any of the three web-sites listed below:
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