Supervisory personnel experience
Not only is the companies’ experience important, but the supervisor must also have a good track record. One should specify the experience level required at the project site.
Alternatively, specifying the number of projects of the same size and scope should be considered. Section 03 30 00 usually requires use of an American Concrete Institute (ACI)-certified concrete flatwork finisher, but this is not enough. An ACI certification does not address concrete slabs that are to be polished; it is better to require both an ACI-certified finisher and someone experienced in polishing concrete slabs.
Quality control plan
Requiring a QC plan is an excellent method to ensure the contractor understands the scope of work and the effect on the polished floor quality of nuances in placing, finishing, and curing on the polished floor quality. For instance, hand-finishing near the slab edges or around penetrations or columns results in a different concrete surface density than that produced by a power trowel machine. This difference will be exposed during polishing.
Preinstallation conference
The preinstallation conference should include the concrete contractor, ready-mix producer, polishing contractor, testing agency, construction manager, and representatives of the architect, engineer, slab consultant, and owner. This meeting should be conducted by experienced individuals who understand both the impact of concrete installation on final polish, and the proper design, detailing, and installation techniques required.
Such a conference helps minimize misunderstandings and reviews project conditions that might significantly affect the work. A checklist should be developed to guide the metting, and minutes should be taken and distributed.
Mockups
One should also require creation of a mockup using the same materials, methods, and personnel to be used on the project. A 40-m2 (400-sf) mockup including contraction joints and concrete from two trucks would be satisfactory. Smaller mockups do not effectively include all the items part of a larger slab. It is also important to leave half of the mockup exposed and unpolished—this way, it can be used to evaluate both the concrete contractor and polishing contractor’s work.
The timing of polishing the mockup should represent the anticipated delay between floor placement and polishing of the actual slab. If hand-finishing will be a part of the finished slab, it must also be part of the mockup. Finally, part of the mockup should be damaged and then repaired so the effect of the repair process can be evaluated for the polished surface.
Identifying the differences: Part 3–Execution
The differences should be specified as necessary in Part 1–General, Part 2–Products, and Part 3–Execution. (The QA and QC provisions have already been discussed.)
Proper concrete for polishing requires good execution. The following illustrates recommended specification requirements for use in Part 3.
Preparation
Place, protect, and repair sheet vapor retarder in accordance with ASTM E 1643, Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs, and with manufacturer’s written instructions. Lap joints 150 mm (6 in.) and seal with manufacturer-recommended tape.
Rationale: Moisture affects the polished surface appearance. If a vapor retarder is specified, the slab should also be reinforced with steel or welded wire that has a cross-sectional area of steel less than 10 percent of the concrete cross-sectional area, and continuous below saw cuts to minimize dominant joint activation. Concrete slabs on vapor retarders slip, causing some joints to not open. This can allow the concrete shrinkage shortening to accumulate at one wide dominant joint.
Placement
Deposit concrete in a continuous operation that does not result in coarse aggregate segregation.
Rationale: If the concrete is dumped into piles and then raked out, coarse aggregate can ‘stack,’ distribution will not be uniform, and the non-uniform coarse aggregate distribution will show through the polished surface.
WOW! You guys really put some quality thought into this! I really appreciate the fact that is was designed to be viewed on a monitor with slides and the fact that you included the very rare WHYS!!!
Great article. Out here in Seattle we are using 22%-30% slag cement. How did you arrive at the recommendation for 20% maximum? -David Landrey, CSI, ACI, LEED AP
Please do this for slabs to receive resilient flooring & the inherent issue of ASTM F710 & spray on curing compounds / moisture sealer spray on products. So many spec writers seem to write a ‘belt & suspenders’ approach when doing both just creates a situation where the belt doesn’t warrant the suspenders’ performance and vice-versa.
Great Read, I love concrete Polishing, we just started doing more and more of those these days.
We keep getting scratches in slag mixes.
There are many light colored scratches that require additional cutting to remove
Many of our mixes are 40% slag.
Has anyone had this experience with slag mixes.