A polished concrete floor can be a beautiful thing, but there’s no way to make a silk purse of a sow’s ear, as the saying goes. As was pointed out at the Creating the Canvas for Polished Concrete session at the 2016 ASCC Annual Conference, a big part of the success of a polishing project is determined long before the polishing contractor arrives at the jobsite.
Some of the owner’s impression of what constitutes a great polished floor starts with expectation. Greg Hyde Hryniewicz said during the session, “Sometimes I just tell the owner that this is not the solution for you, or if they persist, I say, sorry, but I don’t want this job.”
“When we first look at a floor,” explained Chad Gill, “I can tell what it can and can’t do. If they only want to pay for a Volkswagen but expect a MacLaren then that’s a problem. You have to start with the mock-up. It should be a line item in the bid and you sometimes have to fight to keep it. And you have to make sure the mock-up is as much like the actual floor as possible, including joints and edges.”
“You have to emphasize from the start,” said Hryniewicz, “that if they want a great polished concrete floor they are going to have to spend some money and not just on me but also on the finishers and on the maintenance.” Gill agreed: “You have to create the expectation that the place-and-finish contractor and the polisher need to be connected, need to be a team. They both need to go to the owner together.”
In creating a mock-up, said Bruce Suprenant, “Don’t set the bar too high. Have two different trucks bring concrete 40 minutes apart, each with a different slump, even a different mix and a slightly different color. And put a crack in the mock-up by placing a triangular piece of wood in the bottom of the slab. That will create a straight crack but still a crack. Then do a repair on part of the mock-up and polish that.”
“We put some rebar in the mock-up,” said Byron Klemaske, T.B. Penick, from the audience, “because the rock rolls off the bars and that too can create a color or aggregate exposure difference.”
“If the mock-up is too expensive,” said Suprenant, “you can always show the owner a reference sample—take them to one of your recent jobs.” And, he cautioned, don’t let them pick and choose. “The worst thing is if you do the mock-up and the owner circles one spot and says, ‘we want this.’ The mock-up can’t be perfect. Tell your crew that if the first mock-up is accepted then they are fired! What we want is a mediocre mock-up. Then you can over-perform on the floor.”
Place and Finish
A good canvas for a polished concrete floor is not simply a quality concrete floor. “If the spec tells the concrete contractor that this is the same old concrete floor,” said Suprenant, “then as the polishing contractor you’ve got a problem. The spec needs to indicate that this slab is different. At least it needs to get the place-and-finish contractor asking questions. What the polishing contractor needs most is uniform surface density.”
A few tips given for achieving that uniformity were:
- Don’t leave the vibrating screed in one place for too long.
- Don’t use a highway straightedge, it cuts off the paste on high spots.
- Minimize hand finishing and trowel marks; try to get the power trowel as close to the edge as possible. Edges are 90% of the problems.
- You’ll get a better polished finish without fly ash in the mix.
- As part of the ASCC session, a concrete slab was placed with several defects that showed up when it was then polished. Check out the photos for examples.
On Monday at the World of Concrete, Pat Harrison and Bryan Birdwell will present a 3-hour seminar on this topic (MO06).