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| RetroPlate and acid stain on gray concrete. Photo courtesy of RetroPlate. |
Polished Perspectives: Getting the Mix Right for Polished Concrete
Mix design should be looked at as the foundation for successfully marrying design and performance expectations. And what are the most important ingredients of mix design? Education and communication!
by Pete Wagner
Architects randomly pulling ingredients off a shelf? Engineers wanting to prove they have the perfect solution? Owners going overboard in their expectations? Ready mix operators using what they have in their silos?
Mix design should be looked at as the foundation for successfully marrying design and performance expectations. And what are the most important ingredients of mix design? Education and communication!
Polished concrete brings many new equations to the table when it is specified. First, but often overlooked, is exactly where it should be placed in the specifications. What is polished concrete? Is it part of the Construction Specification Institute's (CSI) 2004 Master Format of Division 3 for Concrete, or is it part of Division 9 Special Finishes, or is it both?
During my years as a Certified Applicator for RetroPlate, we tended to take the shotgun approach and hit both divisions, but too often people use only Division 9 and the specification becomes an " I didn't budget for that" item. Today, in my position as marketing director for RetroPlate, I have far greater interaction with both specification professionals in architectural firms and quality-control experts in the ready mix industry, and it appears as though Division 3 is the clear winner.
Fred Herbold, CSS, CSI with SERA Architects in Portland, Ore., says he sees polished concrete as part of the placement criteria and feels that the opportunity for bidders to miss the specification is too easy if placed in Division 9. And from the ready mix side, Tony Allison, Glacier Northwest's head of quality control in Portland, notes the importance of knowing the end use and expectations while designing the mix. As he pointed out to me, the types of materials that are readily available locally will affect the components of the mix as well as what percentage of each component (sand, aggregate, cement, water, additives) is necessary to deliver the expected results. For example, in the 250 miles between Seattle and Eugene, Ore., the different types of naturally occurring aggregate can change the necessary cement requirements three times. If you're an engineer located in Pittsburg who is designing a mix to be poured in Portland, don't make the assumption that the aggregate will be the same. Instead, assume that it won't be. Local knowledge translates into greater success, along with better cost control.
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