Durability, shine and aesthetics
By DANIEL REALE-CHINConcrete Construction
Polished concrete floors are one smooth option that is not only durable, it’s eye catching as well.
Concrete polishing produces floors that are extremely durable, easyto- clean and provide a polished look that many clients are looking for in their buildings.
With applications ranging from large, commercial buildings like warehouses where a client’s main focus may be durability, to commercial gyms where the desire for polish is mainly aesthetic, there are many reasons a client might choose a polished-concrete floor, so it is important to work with the building owner to understand what they want, and what can be delivered, when it comes to polished concrete surfaces.
Communication can help avoid pitfalls, since the multi-step process used to create these surfaces involves navigating variables in the concrete, and ensuring that you and your client are on the same page.
MANAGING CUSTOMER EXPECTATIONS
There are certain aesthetic expectations that customers tend to have when it comes to polished concrete, but between the architect bidding the project and the end-user, the reality of what can be achieved with a polished concrete floor may get lost in translation. If the only discussion about the finished floors has been between the architect and their customer, there is a risk of vision and deliverable misalignment.
Managing expectations starts with making sure the end customer understands the process. Creating polished concrete floors begins with grinding the surface of the concrete using diamond tooling as an abrasive. Although the process produces a smooth surface, there can be a considerable variation in the end deliverable.
“The first question a contractor should ask is, are you looking for a very consistent, monolithic looking floor?” says Randy Wheelis, product training specialist for Bartell Global.
Polishing concrete is a beautification process, but like people, Wheelis explains that all concrete has personality. Through the process of grinding, densifying and polishing, Wheelis says that the personality of the floor will be brought to the forefront.
“By polishing the concrete, you reveal what is already there,” he explains. “Your customer needs to understand that any imperfection in the concrete like cracks, spalling marks, etc., those are going to be visible when you are done.”
Many customers are looking for the unique look that each polished-concrete floor retains, embracing how its cracks and imperfections create a truly one-of-a-kind project, but Wheelis advises that customers still need to be made aware of this lack of uniformity. “As long as your customer knows that they will not get a standard monolithic look, as a professional, you can proceed,” he says.
WHAT CAN BE ACHIEVED
Paul Bravo, president of Bravo Cement Contracting, has worked on a variety of projects for clients, ranging from schools to commercial warehouses. He says part of managing expectations is being upfront and properly illustrating the different finishes possible with this technique.
“When it comes to new-construction projects, there can be confusion between the architect hiring a concrete polishing contractor and the end-user who wants to achieve something very specific with their floors,” says Bravo.
Within his client base, there are three finishes that customers tend to ask for: a cream finish, a salt and pepper finish, and an aggregate finish. Bravo finds that architects are usually referring to the level of aggregate exposure when they ask for any of those finishes.
For some, the concept of a polished floor means that aggregate in the concrete will be exposed through the process of grinding. Bravo explains that a cream finish won’t expose any aggregate, however, adding that it is possible to achieve a finish that is closer to a monolithic look.
A salt-and-pepper finish exposes aggregates like sand and the occasional larger stone, while a full-aggregate exposure is closer to a terrazzo look, with large pieces exposed throughout the floor. The amount of aggregate exposure that can be achieved depends on the diamond grit used to polish the concrete. A coarse-grit diamond disc, which can execute a deeper cut into the concrete, will get the polisher closer to achieving an appearance similar to terrazzo.
Wheelis also abides by a certain set of definitions that help dispel some of the miscommunication that can happen with concrete and polished-concrete literacy. As with Bravo, is aim is for clients and contractors to share the same definition of what each finish is, and how it can be achieved. Wheelis classifies finishes into four categories, ranging from a cream finish, a salt and pepper finish, and then two aggregate looks: a medium or a large aggregate exposure. With each level of exposure, Wheelis says the cut made in the concrete will be deeper.
“But even between these categories, you may find some larger aggregates in a salt and pepper look in random areas because, remember, you will never achieve that completely monolithic look,” he says.
For his clients, Bravo recommends the full-aggregate exposure. That look, he says, can be more forgiving, given the depth that the contractor is cutting into the surface.
Lately, Bravo has noticed a trend with school boards asking for polished concrete, and opting for a cream or salt-and-pepper finish. In schools, he says that look is often hard to achieve because of the unequal lay of the floor.
“You also need to keep in mind that these finishes cannot be achieved on all floors,” he says. “Cream finishes and finishes with little aggregate exposure require very flat surfaces if you want to get an even look.”
Both Bravo and Wheelis note a trend toward a cream finish for concrete floors. That is a look that it can be hard to achieve, and might not be possible, in some cases.
“If I have a client who is requesting a cream finish, I have to make sure that they know that they might get a bit of aggregate if there’s a high spot in the floor, because we often can’t do anything about high spots and concrete,” says Wheelis.
“What often happens is the contracting company will polish the floor, give the client a cream finish, and it will not look as uniform as they expected,” says Bravo, explaining that the limits of the finish can lead to a dissatisfied building owner, which illustrates the need for proper communication.
To achieve the desired level of exposure, abrasives are a must. Wheelis explains that polishing to a salt-and-pepper- or heavy-aggregate exposure usually begins with a 40-grit metal bond diamond. Diamond grit can range from as low as six grit to as high as 300 grit. Some manufacturers even offer higher grit levels than that. His company, Bartell, carries four profiles, ranging from 16- to 150-grit.
The company’s 16-grit profile is its most aggressive, and is recommended for removing coatings like epoxy or glue. Wheelis says a 40-grit profile provides an average scratch, which he recommends for rough concrete, thin coating materials or to expose aggregate. For new concrete, he says 80-grit is a popular choice.
The abrasives are used in succession, each removing the previous grit’s scratch pattern as the machine operator works towards a smooth, scratch-free surface.
FOR THE SHINE
Once the grinding is finished, it is time to add a liquid densifier. Wheelis explains that his choice of a chemical densifier is sodium silicate because of its proven effectiveness for over 70 years, but there are many densifier options, including lithium silicates.
A densifier creates a reaction between the lime in the concrete and a chemical that fills in the small spaces in the concrete, which is porus. The result is a dense floor that should holds up to impact.
“I think people tend to forget that densifying is a chemical process. Densifiers harden over time to make the concrete durable. It hardens right away, but because it’s causing a chemical reaction, that can take more than nine months for the chemical reaction to make the concrete as hard as it will be in the end,” says Wheelis.
Once the concrete densifier has cured appropriately, the client can select a final surface gloss, ranging from almost no gloss all the way to a reflective shine. Burnishing, the process of using a high-speed burnisher to heat, melt and shine a chemical product to the concrete surface is the start of building the shine.
This is another key area where Bravo recommends checking in with your customer, or asking the architect who bid the job to, to gauge what the customer wants to achieve with their polished floor.
Wheelis says that gloss meters are often used as a scale to measure the amount of light reflecting off the floor. He ranks a floors’ amount of gloss into four levels. Level one has little-to-no sheen, and registers as “no reading” on the scale. Level two provides the customer with a low-to-medium sheen and matte or satin appearance with slight reflection and registers at a 40-to-50 reading on the scale.
Level three has a medium-to-high sheen, where an observer can identify an object, but the image is not sharp. This registers at a 50-to-60 reading. Level four delivers a highly polished sheen with a high amount of light reflection and a gloss reading of between 60 and 80.
Being able to present architects with a chart can ensure that all parties are again on the same page as the client selects the level of final polishing for their concrete.
“Architects are often the ones specifying the level of aggregate that the client wants, and what they want to achieve with their floors, but most of the time, what it takes to make sure that a client is going to end up with a product they’re satisfied with is a conversation between the concrete polishing company and the client, directly,” says Bravo.
Bravo suggests doing a site walkthrough or having a conversation with the client prior to tender, since different aggregate exposures, gloss finishes and protectants can require different processes, amounts of work, and therefore more money.
“Beyond that, it is always critical to do a test area to show the customer – the end-user – what the floor is going to look like,” adds Wheelis.