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For years flooring installers have blamed concrete substrate headaches on the concrete contractors. So what is the concrete side of the industry doing to address the needs of the flooring installer? Well, there are actually cement/concrete associations that do understand the frustrations of the flooring contractor and have printed materials addressing the needs of both the concrete contractor and the flooring contractor. The American Society of Concrete Contractors ( and the American Concrete Institute ( are two associations that have literature available.

Following are some of the concrete resources available: 302.2R-06: Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials; 302.1R-04: Guide for Concrete Floor and Slab Construction; ACI 117-06 Specifications for Tolerances for Concrete Construction and Materials and Commentary; “Concrete Floors and Moisture” by Howard M. Kanare.

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Many of the flatness problems we deal with are due to the fact that in project specification manuals, division three and division nine specifications are not compatible. On the concrete side of the industry, concrete contractors are required to follow ASTM E1155-96, “Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers. The F-Number System is the American Concrete Institute (ACI 117) and Canadian Standards Association (CSA A23.1) standard for the specification and measurement of concrete floor flatness and levelness.  F-Numbers replace the familiar “1/8th inch in ten feet.”

The test method utilizes a “dip stick” or F meter that is run across the slab to accurately determine the flatness and levelness of the surface. Measurements are then transferred electronically to a data sheet to give a blueprint of the surface deviations.  

There is no F-Number equivalent to any straightedge spec. But, rough equivalents, in terms of horizontal readings, can be given: an FF 25 is roughly equivalent to a single ± ¼-inch defect in 10 feet; an FF 50 is roughly equivalent to a single ± 1/8-inch defect in 10 feet. 

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There are some manufacturers/associations taking a position that there should be an FF number measurement two weeks prior to an installation with readings across all construction joints and a tolerance of 1/8” in ten foot radius. The ten foot “radius” is also an issue as tests are conducted with the meters in one direction only, they do not run perpendicular tests. This is where there is a disconnection. The ASTM E1155 states that testing needs to be done within 72 hours after placement of concrete and no measurement lines within two feet of any slab boundary, construction joint, isolation joint, blockout, penetration, or other discontinuity. On the flooring side of the industry we are to test flatness of slabs using a ten foot straight edge at any given point. My question here is how many installers out there are checking slab flatness with a ten-foot straightedge?? That’s what I thought. I know that there are a few installers that use a ten-foot straight edge but that is only a small number compared to the six foot straight edges that are used on a daily basis (Photos 1 and 2). So if the majority of installers are using a six-foot straight edge, where did we get the requirement of a ten-foot straight edge? The requirements are taken from the highway department. A ten-foot or longer highway straight edge, also known as a paver’s straightedge is used to cut or plane the surface of the concrete while it is still in what the concrete industry refers to as plastic, hard enough that it holds its shape but still soft enough to cut or plane. Most finish contractors will screed and then bull float but not do a final straight edge cut as they feel it takes too much time; they already have a difficult time with vapor barriers placed directly beneath the slab in regards to edge curling, which is a whole other article. Photo 3 shows a 4-foot bull float and a 12-foot straight edge. This next statement was taken from a highway specification

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Straight Edge: Immediately following the floating, and while the concrete is still plastic, the contractor shall test the pavement surface for trueness by means of a ten foot straight edge. All variations greater than one-fourth inch in ten feet of length shall be eliminated by filling depressions with fresh concrete and striking off projections and then re-floating.

So now you know where the flooring industry got its tolerances for concrete flatness.

Wouldn’t it be great if division 3 and division 9 of the project specification manual stated; “Cement/concrete, and flooring contractors; please refer to divisions 3- concrete, and 9- finishes, to determine if mix designs and finish specifications coincide with flooring manufacturers concrete substrate requirements. If there are concerns, please address to architect or responsible parties prior to bidding.”

What would this require? That the architect, engineering, design, and specification writing communities to work together and print this into their job specifications.

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Not all the blame goes to the concrete contractor in regards to slab conditions; the general contractor and other trades have a place in the chain of responsibility with other factors also. Photos 4 and 5 show a basement slab that has had moisture intrusion and a wood sub-floor with nothing being done to remove or avoid as much of the moisture as possible. The two photos resemble common occurrences in regards to new construction building. This is exactly why installers/retailers need to conduct proper moisture testing procedures or make certain that moisture testing was conducted. Ignorance does not mean innocence; if the installer/retailer does not conduct moisture tests or make certain that a moisture test was conducted they may be held responsible for more than just the labor in most cases.  

The Floor Covering Industry White Paper Position Statement on Moisture Emission Testing/ Moisture Emission Testing Responsibility and Qualifications forTesting, is a document that addresses the need for third party independent testing, available for free download at:

Another area of concern for installers is lightweight concrete and gypsum-based substrates. These types of products are used for less dead load weight (constant weight on a structure) and sound suppression.

There are no ASTM test methods to determine accurate moisture vapor emissions rates in either of these. About the only tests that can be conducted are the ASTM D-4263 “Mat” test, and some electronic meters that read a gypsum base, keep in mind these are only used as indicators. Between gypsum and lightweight pours, gypsum based substrates (2,000 p.s.i.) have much lower compressive strengths than standard concrete (3,000 p.s.i.), which explains why you can take the end of a screwdriver and gouge the surface of the substrate. This type of substrate makes it extremely difficult for installers, as most manufacturers will not warranty a direct-glue over a gypsum based substrate and many times, installers do not know what substrate they will be installing over until the day of installation. There are installations that are being installed on a day to day basis as glue-direct directly over gypsum based substrates even though they will not be warranted, so what happens? It’s a roll of the dice. Some installers will apply a latex/acrylic primer for bond strength, sometimes this works, sometimes it doesn’t. The bond between the adhesive and the primer usually won’t fail; it’s between the primer and the gypsum that will fail. Installers who understand this try to persuade the end user or retailer to install floating floor systems or other flooring that does not require adhesive for bonding. If that’s not enough of a headache with gypsum, you also have the movement issues. Gypsum poured over a plywood substrate can also have deflection issues which causes the gypsum to fracture. Photo 6 shows a subfloor that required support at the plywood joints then a self leveling gypsum product was used to fill the rest of the area, this was done after three flooring failures. There are manufacturers that have membrane systems and gypsum based self leveling products with a higher p.s.i. that are placed over an existing gypsum sub-floor, make sure to check with both the flooring manufacturer and the product manufacturer for acceptance of these types of installations. Also, when using a patching compound over a gypsum sub-floor use the white gypsum based patching compounds, they are compatible with gypsum pours. A Portland-based patching compound will cause a chemical reaction that could lead to bonding issues.

We all have a responsibility to provide the end user with quality products and installation. As the saying goes, it starts from the GROUND UP!!