Preparing Concrete for Resilient Floor Installations

Identifying issues and following recognized standards helps assure best results
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Sponsored by nora
By Peter J. Arsenault, FAIA, NCARB, LEED AP

The standard goes on to indicate some of the reasons for cracking. One of the biggest and most common ones is too much water being introduced into the concrete before, during, or after it is poured. Hence, the importance and significance of the water-to-cement ratio is highlighted along with references back to places in the standard that address that.

Other causes of cracking include the inability of the slab to overcome restraint from forms, other structural members, etc. Therefore, the proper use of control and expansion joints is needed to channel the forces of the concrete-curing process and minimize any cracking. If cracking is limited to a spider-web network of very tiny, shallow cracks on the surface of the floor slab, this is referred to as crazing. This phenomenon usually occurs as a result of too much water remaining on the surface when the concrete is curing and/or drying.

For resilient-flooring installations, some limited amount of cracking is certainly to be expected and is workable using appropriate floor patching or filler. However, large, wide cracks or cracks that run across a large section of the floor can be a problem since that irregularity may telegraph up through the flooring material and be visible. Crazing will be less of an issue unless it causes the top surface of the floor slab to deteriorate and break apart, thus losing its value as a resilient flooring underlayment.

  • Low wear resistance: This aspect of concrete is more typically a problem when the concrete also acts as the finish flooring. In the case of adding resilient flooring over the top, it is an issue only to the extent that the concrete breaks down under the flooring and creates problems for the resilient flooring. This can happen primarily when too much water is present in the concrete mix. In this case, the heavier, denser aspects of the concrete settle to the bottom and the lighter, more watery portions settle on the top. This creates a condition where the least wear-resistant concrete is in the worst possible place: on the surface. Hence, careful attention to the water-cement ratio and the amount of water used in curing is an important consideration to avoid this problem.

The surface of a concrete floor needs to be examined and assessed for conditions that could cause potential problems with resilient flooring placed over it.

  • Dusting: When the poor surface conditions described above occur, it can also cause dusting of the surface. Dusting is defined as “the development of a fine, powdery surface that easily rubs off the surface of hardened concrete.” This is an obvious problem for adhered flooring in that the adhesives will stick to the powdery dusting but not necessarily the hardened concrete below it.
  • Scaling: This condition is described as “the loss of surface mortar and mortar surrounding the coarse-aggregate particles.” This irregular surface can cause issues with flooring in that the coarse texture may cause irregularities in the flooring surface and also complicate any adhesion. Scaling is often caused by freezing within the concrete, not a chemical reaction. It may also occur if entrained air is not present to absorb pressure changes or if de-icers are used that rapidly deteriorate the concrete.
  • Popouts: This is a condition that occurs primarily when impurities are found in the concrete mix, creating a small area that does not bond properly and literally pops out of the surface. It can be an obvious problem for resilient flooring in that it will leave the concrete surface with holes and pock marks that may not be tolerated by the flooring. This situation is avoided by careful attention to the mix for purity and, in some cases, by using wet-curing methods that have been shown to greatly reduce popouts caused by alkali-aggregate activity.
  • Blisters and delamination: If air is trapped between the surface of the concrete and the remainder of the slab, then blisters (air pockets at the surface) or even delamination of the slab can occur. That will cause problems for resilient flooring if the blisters pop or the flooring is not fully attached to the concrete. ACI 302.1 provides eight ways to avoid blistering depending on the conditions encountered, and they should be followed accordingly.
  • Spalling: This is a deeper condition than those described so far and can lead to breaks along the lines of reinforcing steel or layers of concrete in multi-layer construction. It can also occur along joint lines where the joint construction is improper. Any of these conditions can create inferior conditions for a finished slab intended to receive resilient flooring. Therefore, the advice contained in this part of ACI 302.1 should be reviewed and implemented.
  • Curling: This is defined as “the distortion (rising up) of a slab’s corners and edges due to difference in moisture content or temperature between the top and bottom of a slab.” Curling may make it appear that there is a problem with the resilient flooring, but in fact it is a concrete floor issue. ACI 302.1 provides a variety of ways to help avoid this problem related to the materials, slab pouring conditions, and workmanship.
  • Analysis of surface imperfections: In the event that any of the above problem conditions are believed to be occurring, ACI 302.1 recommends the use of a petrographic (microscopic) analysis on 4-inch-diameter samples of the concrete. Based on a review and analysis by a petrographer, designer, or concrete technologist, the proper problem can be identified and remedies determined to make the slab suitable to receive resilient flooring.

Overall, perhaps the most notable significance of ACI 302.1 is that it is well-known, followed, and understood by those trades that provide concrete work. However, it is equally important that those involved in flooring understand that this is the basis for most concrete floor work in terms of construction quality and suitability for construction.

Preparing Concrete Floors to Receive Resilient Flooring

Once the concrete floor is constructed, the flooring subcontractor is then faced with the task of evaluating the suitability of the slab for receiving the resilient flooring. As noted previously, it is better if a flooring representative is involved before, during, and after the construction of the concrete floor slabs. However, regardless of the project and site circumstances, the flooring contractor’s scope of work typically includes some preparation work on the concrete before the flooring is installed. In this case, the standard-practice guideline is ASTM F710-17: Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring. This standard, like most ASTM standards, is developed by a committee of people representing different parts of the flooring industry. It is regularly updated based on the latest technical information and feedback from users, manufacturers, and others in the industry.

ASTM F710-17 essentially defines the ways to assess the suitability of a concrete floor and some remedial action if needed for the installation of resilient flooring. It includes suggestions for the construction of a concrete floor that are generally in sync with ACI 302.1 and are intended to help assure that the concrete floor is acceptable from the outset. Note that ASTM F710 does not cover structural performance of the floor but is focused on the necessary preparation of concrete floors prior to the installation of resilient flooring. It is also not intended to supersede the instructions or recommendations of manufacturers of specific resilient flooring or adhesives.

After some introductory information on scope, referenced standards, and terminology, ASTM F710 is broken down into four primary sections:

  • General guidelines: Some general guidelines are provided that are fundamentally applicable to all concrete floors–both slabs on ground and above grade. The first of which is a “permanent, effective moisture vapor retarder…as described in [ASTM] E1745 is required under all on- or below-grade concrete floors.” This reiterates and reinforces the stance described ACI 302.1 above on the proper use of vapor retarders.

 

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Originally published in Architectural Record

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