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Standards for Repair of Cracks in Poured Concrete Floors InspectAPedia®  -

• Standards for Repair of Cracks in Poured Concrete Floors
• How much out of level is allowed on a concrete floor slab?
• How wide or big a crack is allowed in a concrete slab?
• When is a concrete floor crack a trip hazard?
• Other reasons to seal or repair cracks in concrete slabs or floors

This article describes some Standards for Repair of Cracks in Poured Concrete Floors. This website describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.

Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history, and other evidence of building movement and damage are described to assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from those likely to be important and potentially costly to repair.

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Standards for the Acceptance or Repair of Cracks in Concrete Floors in New Construction

Settlement cracks may form a tripping hazard even if they are not traced to a structural concern. While there are few construction acceptance standards for floor slab cracking, one, "Quality Standards for the Professional Remodeling Industry" NAHB, , recommends that cracks in basement floors which exceed 3/16" in width or 1/8" in vertical displacement should be repaired.

The same standard provides that cracks in slab-on-grade floors shall not exceed 1/16" in width or in vertical displacement. The same standard provides that cracks occurring in control joints in concrete slabs are normal and acceptable. [We suggest that this last criteria should apply to crack width but not to vertical displacement.]

Measurements of the degree of levelness or flatness of concrete slabs and floors

How to Slab "F" numbers to describe the flatness and levelness of a poured concrete slab

The traditional objective for levelness of a poured concrete slab was that the slab could be tipped or concave or convex in an amount equal to or less than 1/8" in 10' of slab surface in any direction. A perfectly uniform surface might tip from one end to the other by up to 1/8" across a ten foot distance and still be acceptable.

However other conditions of variation in concrete slab surface flatness and degree of levelness occur, such as variations out of flatness level at other intervals across the same distance - making such measurements and standards ambiguous. An "F-number" system is currently used to describe the degree to which a poured concrete floor or slab is flat and level.

The formulas for "F" are more complex than just using a level and tape measure:

• Slab flatness: F_F = 4.57 / ((3 x Sq) + (the absolute value of the mean value of q)) where Sq is the standard deviation of q, and "q" is the variation in height over any given 12" distance or interval across the slab.
• Slab levelness: F_L = 12.5 / ((3 x Sz) + (the absolute value of z)) where Sz is the standard deviation of z, and "z" is the total change in elevation from one edge to the other of the poured concrete slab across ten feet in any direction.

A little online course and tables of recommended "F" numbers to provide a standard for flatness and levelness for different types of poured concrete floors is at Technical Reviewers below.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

• "Concrete Slab Finishes and the Use of the F-number System", Matthew Stuart, P.E., S.E., F.ASCE, online course at www.pdhonline.org/courses/s130/s130.htm
• "Best Practices for Concrete Sidewalk Construction," Balvant rajani, Canadian National Research Council
• "Design Considerations for Perlite Roof Slabs," a chapter in "Perlite Concrete Grade for Lightweight Concrete Construction", United Perlite Corporation
• "Quality Standards for the Professional Remodeling Industry", National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987. See our books at "Structure" at the InspectAPedia Bookstore
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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