Hardwood Floors April/May 2017

Understanding Concrete Floor Flatness Tolerances

Construction joints , also known as cold joints, are used where two successive placements of concrete meet. This cold joint becomes a weakened joint that will crack when either slab moves.

In new construction (most commonly commercial), concrete contractors pour and set the concrete subfloor to meet a minimum flatness tolerance in accordance with American Society of Concrete Contractors (ASCC) Division 3 requirements, tested in accordance with ASTM E1155. Division 9 specifications for concrete floor flatness tolerances specify floor flatness requirements for floor coverings and differ from Division 3 requirements. The concrete contractors seldom receive Division 9 specifications when bidding the project, because the floor covering often hasn’t been chosen yet. Concrete contractors are responsible for meeting the requirements of Division 3 specifications for floor flatness. ASCC, NWFA, National Tile Contractors Association (NTCA), and Flooring Contractors Association (FCICA) suggest the owner provide a bid allowance, established by the architect/design professional, and based on the floor covering requirements, for any necessary grinding and patching to close the gap between Division 3 and Division 9 tolerances. Providing this allowance enables the owner to compare floor covering bids on an equal basis. If you have any questions about concrete floor flatness tolerances, contact your ASCC concrete contractor, the ASCC Technical Hotline at 800.331.0668, the NWFA at 800.422.4556, or the FCICA at 248.661.5015.

Control joints , also known as contraction joints or saw cut joints, are formed, sawed, or tooled grooves in the concrete slab used to induce shrinkage cracking at specific locations.

Isolation joints are a separation between adjoining parts of a concrete structure, usually a vertical plane, at a designated location used to prevent a bond and allow movement between the slab and the adjoining structure.

The NWFA provides a Jobsite Checklist that can aid in checking the concrete subfloor before each job. The Jobsite Checklist is available on page 91 of this issue of Hardwood Floors Magazine and can be customized with your company info and downloaded by visiting nwfa.org. For more information, contact the NWFA at 800.422.4556. Brett Miller is VP of Certification and Education at the National Wood Flooring Association in St. Louis. He can be reached at brett.miller@nwfa.org.

the magazine of the national wood flooring association

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