Concrete Polishing Association of America

CPAA RECOMMENDATIONS FOR THE
DESIGN, SPECIFICATION, AND PLACEMENT
OF CONCRETE FLOOR SLABS

The successful completion of a diamond polished floor is dependent on two important factors: 

 

CPAA offers guide specifications to design professionals and the construction industry that addresses the second of these two important factors, however, the diamond polishing company has no control over the design, specification, or placement of the concrete floor slabs that are to be polished.  To address the first of these two important factors, CPAA recommends the following design and construction recommendations be evaluated for inclusion in the Division 03 cast-in-place concrete specifications prepared by the project structural engineer.

DIAMOND POLISHED CONCRETE IS NOT TERRAZZO

A diamond polished concrete floor is not like terrazzo:

 

The point is that a diamond polished concrete floor cannot be thought of as a terrazzo floor. It is a different process that is not a covering and depends on heavily on the quality of the concrete.

EARTH SUBGRADE

CPAA recommends fine grading the subgrade uniformly flat using a laser device.

Imperfections in the subgrade surface, such as rises and depressions, could cause variations in the thickness of the concrete which increases the possibility of cracking because of restricted movement.  A uniformly flat subgrade surface reduces the potential of cracking because the concrete slab can expand and contract with minimal friction.  While cracks can be filled during the polishing process, they cannot be made invisible by the polishing contractor.

Also, depressions in the subgrade could allow bleed water to pool on top of the below slab vapor barrier during plastic state of concrete which could cause blemishes in the concrete surface because of the differential curing and drying.  Blemishes such as this cannot be eliminated by the polishing contractor.

BELOW SLAB VAPOR BARRIER

Moisture movement from earth subgrade through the concrete slab-on-grade to the concrete surface is a major problem in the flooring covering industry today, and can adversely affect a polished finish as well.  A high-performance vapor barrier between the subgrade and the concrete is extremely important, therefore CPAA recommends a membrane that is rated Class A according to ASTM E1745 - 09 Standard Specification for Water Vapor Retarders Used in Contact with Solid or Granular Fill under Concrete Slabs that has the following properties:

 

Installation of the vapor barrier should comply with ASTM E1643 - 09 Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs.

CONCRETE MIX DESIGN

In addition to ACI standards for mixing concrete, CPAA recommends the following:

 

PLACING CONCRETE

In addition to ACI standards for placing concrete, CPAA recommends the following:

 

FINISHING CONCRETE

In addition to ACI standards for finishing concrete, CPAA recommends the following:

 

CONCRETE CURING AND DRYING

CPAA recommends evaporation control and wet curing concrete slabs according to ACI 308R-01:  Guide to Curing Concrete (Reapproved 2008) without the use of topically applied curing compounds.  While topically applied curing compounds may assist with curing during the first few days after concrete placement, they retard concrete drying in the weeks and months after curing and may cause the slab to be too wet when the time comes for diamond polishing or floor covering application. 

Densifiers and hardeners should not be applied to concrete.

FLOOR FLATNESS/LEVELNESS CRITERIA

CPAA recommends specifying the following tolerances:

 

Specified Overall Value

Minimum Local Value

FF Floor Flatness

50

35

FL Floor Levelness

30

20

The floor flatness and levelness should be tested within 8 hours after completion of the final troweling operation according to ASTM E1155 - 96(2008) Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers by an independent testing agency experienced with the testing procedure and possessing the necessary equipment.

Additionally, a remedy for out-of-tolerance work should be specified.

CONTRACTION JOINTS

Based on independent studies, CPAA recommends saw-cutting slabs as soon as possible after finishing using a saw blade that has a triangular arbor configuration to reduce edge raveling or dislodging aggregates at the following spacing to minimize slab curling and cracking:


Slab thickness, inches

Spacing, feet on centers each way

4

10

6

12

8

15

Since concrete shrinks during curing and drying in two directions, cracks are minimized when the area between contraction joints is as close to a square as possible.

PROTECTION

CPAA recommends the concrete finishing specification include a requirement that the finished concrete slab comply with the damage and stain prevention provisions specified in the diamond polishing concrete floors specification.

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