Concrete Slab Configuration Raises Concerns Among Sports Flooring Installers

Oakbrook Terrace, IL - Concrete slab configuration is very important in the success of a new maple floor installation.  Placing a below-slab vapor barrier directly beneath the concrete slab is proper and typical.  Placing any type of fill material between the below-slab vapor barrier and the concrete slab frequently causes moisture-related problems with the finished maple surface.

The Maple Flooring Manufacturers Association (MFMA) requires the general contractor to provide a concrete slab troweled smooth and flat to a tolerance of 1/8” in a 10’ radius, subject to the approval of the MFMA wood flooring contractor.  By placing sand between the vapor barrier and the slab, a flatter concrete slab with less initial curling can be produced.  However, this configuration allows the sand to act like a sponge -- trapping moisture within the sand layer during the concrete pour. Over time, trapped moisture can migrate up through the concrete slab and cause moisture-related difficulties with subfloor components and the finished wood flooring surface.

The only MFMA recognized method for reading concrete moisture levels within a slab is by testing its relative humidity. Please refer to the instructions of the manufacturer’s relative humidity test kit for complete details on how to administer the test correctly. MFMA recommends the relative humidity level for a concrete slab for a non-glue-down maple floor system be 85% or lower and for glue down systems the concrete slab relative humidity level should be 75% or lower before installation. For concrete relative humidity conditions above MFMA’s recommendation consult your MFMA Sport Floor Contractor or your MFMA Manufacturer.

Use of this slab configuration published by American Concrete Institute publication “ACI A302.1R-96” may void your MFMA Sport Floor Contractor and/or MFMA Maple Flooring Manufacturer warranties.

For more information regarding variations to MFMA’s recommended concrete slab configuration, please contact MFMA’s Technical Director at 888-480-9138 or email

Released: October 19, 2000   
Updated: November 5, 2015

Revised 01/16
Disclaimer: The MFMA provides general information to architects, specifiers and consumers. The MFMA, its members, officers and agents disclaim any responsibility whatsoever for the accuracy or applicability of these guidelines under all circumstances and conditions.
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