So your client has decided they want a concrete floor? How do you specify the concrete floor to be polished? You can’t just say, “Pour concrete and then polish it.” As more architects specify polished concrete for both residential and commercial uses, it’s important to have everyone speaking the same language.
Many polished concrete specifications are vague, because many of the people doing the specifications are not familiar with the full process. The way the concrete is handled, from the pour to the last trowel, influences the outcome of the polish job. No other flooring option has as much versatility and ease of maintenance as a polished concrete floor, but it must be specified correctly.
Inform the team Concrete suitable for putting tiles or carpet on top of it is usually unsuitable for polishing. Concrete for polishing must be specified differently. When you’re working with a team, including designers and architects, make sure that everyone knows early on that the concrete slab in the prints is specified to be polished. Before installation, ensure that the architect, concrete contractor, ready-mix producer, polishing contractor, testing agency, construction manager, engineer, slab consultant, and project owner know that the project has concrete specified to be polished.
The reason that everyone on the team should be experienced in concrete is because of the details that can affect the outcome of the job. For instance, the use of a vapor retarder on the slab requires that the slab also be reinforced with steel or welded wire. Vapor retarders cause the concrete to slip, which can affect how concrete piles up around the joints.
Choose experience A concrete slab that is to be polished should be poured by someone with experience in finishing concrete to be polished. If there are columns or stairs that will need to be hand-finished, this will result in concrete with a different surface profile than concrete to be finished with a machine.
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 noticeable during the polishing phase. Generally, less hand-finishing when polished concrete is concerned, the better. This is because machine-troweling results in a harder surface density than hand-troweling, which will be obvious in the polished surface.
Request mockups Make mockups using the same materials and methods, as well as the same person doing the work, as will be performed on the job. Determining the mock-up takes some skill as well, so that the size of the mockup is not too small. If a machine will do the polishing, the machine will go over a small sample area more times than it would on the larger floor, due to turning radius. If hand-finishing will be a part of the finished slab, it must also be part of the mockup.
Surface finishing The surface of the concrete slab must have sufficient paste in order to allow for polishing. Hand-screeding will not provide enough surface paste. Too much vibration can push larger aggregate deeper down into the concrete, which can result in surface variations once polishing is complete.
Avoid specifying the number of trowel passes for the finished concrete. There is simply too much variability in the mix design, humidity and temperature, and the types of trowels, to make a specification like this.
Specifications must follow after the desired finish has been determined. If the concrete is new, the specs must include specifications for mix design, finishing, curing, control joint placement, sealant and possibly other parts of the process.
Test for flatness A polished floor requires a highly flat floor, to account for reflectivity. In a polished floor, even minute differences in floor flatness (FF) will be very noticeable. Floor Flatness above 40 will minimize a wavy appearance in a floor. Measure the FF in accordance with ASTM E 1155, Standard Test Method for Determining Floor Flatness and Floor Levelness numbers within 72 hours and at the start of polishing work. This specification helps put everyone on the same page regarding flatness. The retesting right before the polishing work is done accounts for any changes in flatness that may affect the work.
Regardless of whether the concrete is already in place or if it is new, remind all of the other trades doing work in the space that the concrete will be used as the finished floor. Any chemicals, stains, scratches or other surface damage will affect the finish. The concrete in this case is the floor and should be treated accordingly.
Choosing a team that has experience in specifying and processing concrete for a polished concrete floor is the most important detail. Everyone who is working on a concrete floor specified for polished concrete should know what is going on at each step of the way. There are many factors that can affect the outcome. But, ultimately, once the polished concrete floor is finished, the client will end up with a beautiful floor that is easy to maintain.
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