National Floor Covering Association

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Best Practice for Measuring Substrate Flatness for Floor Covering Installations

An industry guide on how to use the 10′ straightedge

JANUARY 2023.  How a floorcovering installer verifies flatness of a substrate provided by the Constructor (GC) using a 10’ straightedge has always been a contentious issue. Without a standard explaining how to take these measurements, those involved are left with uncertainty and the likelihood of disagreement as they try to confirm acceptably flat surfaces before beginning an installation.


In 2021, NFCA assembled a committee of experts to review this issue and come up with a guide that all affected parties can get behind.


Now, for the first time, we are able to publish a comprehensive document that addresses this issue. This will enable constructors (GCs), architects, manufacturers, concrete finishers, floorcovering installers and building owners to get on the same page.


The document includes scope of the best practice, definitions, performing a straightedge test before or after installation, and alternative measurement technologies.


We are providing this to the industry at no cost

You can access it here


In the video below we see an independent testing agency (hired by the constructor) checking a concrete slab for flatness and marking where high and low spots are recorded beyond 3/16” over 10’ (4.7mm over 3m) . A ‘Hardened Concrete Finisher’ will then patch (fill low spots) and grind (remove high spots) as necessary until the entire slab surface has been successfully prepared to meet tolerance (manufacturer’s requirement). Floor covering installation scope begins once the slab is provided thoroughly dry, surface contaminants removed, flat, smooth to correct profile, and at correct temperature.




NFCA extends our deepest appreciation for all the work and countless hours that went into developing this document – a tremendous collective effort.


Don Brletic, President, Beatty Floors Ltd

Seth Pevarnik, Director of Technical Service, Ardex Americas

Keith Robinson, Research & Development/Specifications, Dialog

Graeme Rosen, Technical Sales Representative, Inter Source Trading Company

Clayton W. Shull, Principal, All Flooring Inspections and Forensics

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