Specifying Polished Concrete Floors

When specifying concrete floor work and polished overlayments, there are of course numerous choices and specification details to pay attention to. Coordination with manufacturers during the design phases of a project will help gain insight into details, cost drivers, installation requirements, and finish options. In a standard CSI or MasterSpec format, the usual location to include this spec is in Section 03 35 43 Polished Concrete Finishes. Some of the relevant items to address in a standard 3-part specification format are highlighted as follows.

Part 1 - General

The scope of specification work can include all preparation work, underlayments, primers, overlayment, and finishing. In carrying out the work, the following standards can be referenced including the ASTM F710 standard discussed earlier:

• ASTM C109 – Standard Test Method for Determining the Compressive Strength of Hydraulic Cement Mortars using 2 inch or 50 mm Cube Specimens.

• ASTM C1028 – Standard Test Method for Determining the Static Coefficient of Friction of Ceramic Tile and Other Like Surfaces by the Horizontal Dynamometer Pull-Meter Method.

• ASTM F1869 – Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.

• ASTM F710 – Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring.

• ASTM F2170 – Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In-situ Probes.

• ASTM E430 – Standard Test Methods for Measurement of Gloss of High-Gloss Surface by Abridged Goniophotometry.

• ACI 302. R-04 – Guide for Concrete Floor and Slab Construction.

Submittals for polished concrete floors should include the usual manufacturer’s data and information for all products used plus recommended maintenance and cleaning information to be passed on to the building owner/operators.

Quality assurance is clearly an important part of any field-installed system and the same is true here. It begins with the use of trained installers and applicators with a minimum number of years of experience, up to 10 years recommended by some manufacturers. Evidence of such qualifications can be requested as a submittal, but it is important that the people actually in the field are the ones with the qualifications and experience needed. In some cases, manufacturers offer regular training and it is appropriate to request certificates showing completion of training. As the overall quality basis of the project and before work on the full area begins, the installation team should prepare a mock-up for review and approval.

Protecting products and materials at the site are important. Fortunately, since this work is often done at the very end of a project, the environmental conditions should be controllable. Generally, materials should be installed in an environment between 50 and 80 degrees Fahrenheit. The ideal temperature at the time of installation is 70 degrees Fahrenheit for both the surface and air temperatures. Warmer material will set faster than expected and cooler material will have slower strength gain.

Part 2 - Products

All of the relevant products used in the total system should be called out and specified for a project. Utilize manufacturer’s recommended specifications, proportions, mix ratios, additives and proprietary components as required for specific applications. The specified products can include:

• Concrete repair materials and toppings, including self-leveling concrete underlayment if called for

• Surface defect and crack filler materials

• Primers specified as either epoxy, acrylic or both as appropriate to the project

• Water designated as clean and potable

• Concrete chemical treatments such as densifiers or stain guards

• Appropriate joint or terrazzo strip materials

• Aggregate materials and terrazzo strips should all be agreed to by the designer and the installer, and shall be within recommended guidelines of the manufacturer

• Surface stains, dyes or colorants should be approved by the concrete overlayment manufacturer

In addition to the products used, it is common to call for the type of polishing equipment that should be employed to achieve the desired results. Note that three-phase 480-volt power may be needed in some cases and should be coordinated with the general contractor or the electrician. Three (3) head or four (4) head counter rotating variable speed floor grinders with at least 650 pounds down pressure are recommended. Further, a dust extraction system, pre-separator, and squeegee attachments with minimum flow rating 580 cubic feet per minute can be specified along with hand grinders with dust extraction attachment and pads for final finish work.

Part 3 - Execution

As we have seen, the installation requires multiple steps which need to be clearly articulated in the specification in order to receive best results.

• Examination and Preparation: The importance of this work should be stressed. In addition to the architect, the installer should be given the authority to examine and approve the concrete substrate for conditions affecting the performance of the finish. Further, the installer shall be the one to correct conditions that are found to be out of compliance with the requirements of the system, including the installation of a pre-leveling layer if required. All surface defects shall be repaired and all joints and cracks shall be repaired using materials specified. Ultimately, the goal is to provide a concrete substrate surface that has been mechanically prepared to an acceptable level, is clean of all contaminants, and free of any debris. If the application includes divider/terrazzo strips, then call for setting and levelling them to the appropriate heights prior to the pour of the overlayment. Similarly, the installer shall pin or otherwise mark all existing joint locations to ensure they can be located and re-saw cut after placement of topping.

• Primer: Prime the prepared concrete substrate using the specified primer in accordance with manufacturer’s recommendations and time restrictions. For epoxy primers, washed and kiln dried angular cut silica sand is broadcast to the point of refusal into the wet epoxy. After the epoxy primer cures, all loose silica sand should be vacuumed up.

• Overlayment Mixing: A rapid setting self-leveling overlayment needs to be mixed and installed in accordance with manufacturer’s instructions including careful monitoring of the amount of mix water being used with allowance for the following design items:

• Additional aggregates used shall be approved by the topping manufacturer
• Integral color shall be approved by manufacturer
• Mixing equipment and procedures shall be specified or approved by the manufacturer

• Overlayment Placement: The mixed topping should be placed by pouring, trowelling, or pumping to the levels required and to conform to details on the drawings. The material should be placed to achieve as true and smooth a top surface as possible with mounds or dips deemed not acceptable. The installation contractor shall control overall flatness and levelness.

• Joint Sawing: Allow the topping to cure for a minimum of four (4) hours prior to saw cutting joints. Locate original joint locations and saw cut through topping into the original joint. The saw blade shall penetrate to depth of the original joint or 2" deep, whichever is less. Ensure saw-cut joint is completely free of dust/debris/laitance and apply stain prevention film or other masking agent along surface on both sides of the joint if residual staining may be a concern.

• Install joint filler: Fill from bottom of joint, being careful to avoid entrapping air and slightly overfill joint to a crowned profile. After sufficient cure, razor cut excess filler, leaving a filler profile which is flush with the floor surface. If filler profile is low/concave, remove top of filler and re-apply.

• Polishing: Allow overlayment and fillers to cure for a minimum of 24 hours before beginning the polishing process. Use an overlay polishing system that is approved by the manufacturer.

• Surface Texture: The desired gloss, distinctness-of-image (DOI) or roughness of average (RA) should be identified and selected. These are identified by surface texture ratings that fall into standard categories of A, B, or C finish as noted in the accompanying charts.

• Protection: Once applied, the finish surface needs to be protected during any remaining construction work including final mechanical or electrical trimming, painting, or any punch list work. Since the polished surface is in fact the finish flooring, it needs to be covered and protected just like any other finish flooring. Therefore, protect the surface by means of curing blankets or other protective measures until substantial completion can be achieved.

When specified and installed correctly, the finished floor will meet the demands of both the building owners and the designers.