Looking at Polished Concrete
January 16, 2008
Commercial building owners, both owners of new construction and those planning to remodel existing structures, want good looking, bright, and reflective floors; but they also want floors that are inexpensive to install and easy to maintain. Increasingly, building owners and their architects are turning to polished concrete--not your old industrial grade of concrete floor--but a new generation of decoratively polished concrete that is perfectly suited to today’s high-traffic retail, commercial, industrial and municipal spaces. When properly finished, polished concrete can be spectacularly beautiful and can be a floor that is cost-effective to install and easy to maintain. Polished concrete floors are being used today in such diverse applications as schools, “big box” retailers, automotive dealer show rooms, high-end retail spaces, light industrial spaces, offices, grocery stores, and in warehouse and distribution spaces. Increasingly, we are seeing polished concrete in high-end residential applications, either as a substitute for natural stone or as a preferred material in a modern, environmentally sensitive home.
At Innovatech Products and Equipment Company we manufacture professional grinding and polishing equipment and we sell grinding and polishing systems. Our customer service team at Innovatech is made up of individuals with many years of industry experience, not just experience selling equipment, but on-the-job experience grinding and polishing millions of square feet of concrete floors in hundreds of customer jobsites. We answer a lot of questions about grinding and polishing concrete floors and we also conduct monthly training sessions for our customers. Together, we’ve made about every mistake that can be made. From our combined experience, and from the experiences of our customers, both the good and the not so good, we have come up with a few suggestions and some ideas that may help flooring contractors approach a polished concrete job without loosing their shirts in the process.
We offer here a few of our suggestions and ideas; some are rooted in lessons learned through our own mistakes; some from mistakes made by our customers and more than a few of our ideas grew from our customer’s real success stories.
Some of what follows is pretty simple; like suggesting that you “know the job” before you bid it, but you would be surprised at how often we hear a horror story that came about because somebody forgot to pay attention to the basics and ended up with an unhappy customer, days or weeks of lost time, and with the projected profit of a polished concrete job only a distant and bitter memory.
Let’s start by looking at the “typical” process of polishing a concrete floor. The first point that must be made is that there is no such thing as a “typical” concrete polishing job, because every concrete floor is unique. In a large floor we have seen substantial variation in the density, hardness and composition of the concrete; variation even within the same pour! Sometimes you cross an expansion joint and the concrete is as different as night and day.
There is no use cursing the Fates, that’s just the way it is. A successful concrete polish job requires first the ability to know and understand what the floor is telling you, and second, the ability to adapt to changes in the material.
Still, while there is no “typical” concrete polishing job, there are common approaches and procedures that will help you to resolve problems in an efficient and cost-effective way.
Know the JobKnowing the job requires more than measuring out the area, finding the best access point for mobilization and scratching out your bid. It means defining two sets of variables--the physical conditions at the site and the customer’s expectations.
Let’s look first at the physical variables:
- Is the concrete hard, soft or somewhere in between?
- Is it green? Is it cured? Is it old, as in a remodel?
- Have chemicals been applied at some time in the past to harden or densify the floor?
- If so, what products were used?
- How was the floor worked when it was poured? Is the floor flat?
- Are there ridges, swirls or trowel marks? Joints? Cracks? Lipage?
- If the job is a remodel, what was down on the slab in the past? If removal of the old surface covering is a part of your bid, be sure you know how many layers of material are down and what the adhesives are.
- Are there moisture problems? Any sign of efflorescence?
The second set of variables is really a process of defining the customer’s expectations. Sometimes this is a mutual educational process. You must understand what the customer wants and expects from the finished floor; the customer must understand and accept that there are limits to what is possible within the constraints of the physical conditions, the technology of grinding and polishing and the budget.
There will always be some variation in the finished appearance of the floor. A specification such as, “I want a really shiny floor,” is much too subjective to provide a real standard of performance. You could be there forever. We suggest that you specifying (1) the average light reflectivity of (2) a specified number of test points using (3) a specific model of light reflection meter (4) at a distance of X inches from the floor under (5) ambient lighting conditions as one way to set the definition of when you are done. An alternative may be a “best efforts” standard specifying the number of passes and final grit to be used.
One installer, using a new type of polishing pad, the Innovatech I-Shine Pad System, put on a demonstration for the executives of a big-box “warehouse” retail chain. The installer carefully assessed the existing site conditions, worked his way up through the grits to 3000 grit, producing a beautiful reflective shine-what we sometimes call a “deep clearwater pool” shine, only to note the unhappy look on the faces of his potential customers.
“Look,” one of the executives explained, “this floor is beautiful. The shine is fantastic; but it looks like it belongs in a Nordstrom’s. We are a warehouse club. Our customers expect an industrial warehouse when they come here to shop. This is too shiny. It will never work for our stores.” Fortunately, by going back to 800 grit pads the installer was able to dull-down the shine to exactly the industrial mat finish that the customer wanted.
If you cannot get the customer to agree, in advance, to a specific and measurable definition of “shiny floor” remember that sometimes, with some customers, the smartest decision is to “no bid” the job.
How Many Steps?The process of grinding and polishing concrete floors, reduced to its most basic, is simply a process of repetition. You grind the floor using course grit tooling and, as each successive grit is applied, the scratch pattern of the tooling becomes finer and finer until the floor attains the desired gloss.
“But,” we are asked, “how many steps will it take?”
The answer, of course, is, “It depends…”
Generally, for a floor in average condition, we recommend starting the process with 40 grit metal-bond diamond tooling. After a first pass going north-south and then an east-west pass, switch to 60-80 grit metal-bond tools making two passes, then move to 150 grit. When using a modern polishing pad, such as the Innovatech I-Shine Pad System, we would switch to 200 grit pads, then 400 grit pads and 800 grit. For a mat finish, 800 grit may be enough to bring up the desired level of shine. For a higher gloss floor we follow 800 grit pads with 1500 grit and then, for the ultimate shine, 3000 grit.
If using traditional phenolic tooling, after the 150 grit metal-bond tools we would switch to phenolics starting at 100 grit, then 200, 400, 800, 1500 and 3000 grit.
Sometimes we recommend finishing the floor with a final buff using a plain buffing pad under a high-speed burnisher.
Depending on the condition of the floor, we may apply a chemical hardener/densifier at the 400 grit stage, allowing the hardener to dry overnight.
If the floor is to be colored with a stain or a dye, we recommend application of the coloring product prior to the final steps of the polishing process.
The Economics of Grinding and PolishingTooling wears out, and the lower grits wear out faster than the higher grits. On a 10,000 square foot job, at today’s competitive tooling prices, on average concrete, most experienced contractors will expect to incur tooling costs of about five cents per foot per step, with each pass over the floor counting as one step. For an eight-step process, that’s forty cents per foot in tooling costs alone. Now add in the cost of machine amortization, the cost of applied chemicals, labor and your profit. Regional costs and conditions differ, but in most areas of the United States our customers report that they are bidding 10,000- square-foot grinding and polishing jobs at about $3 per finished foot plus $1.50 per linear foot for edge work.
The key to customer acceptance of polished concrete floors seems to be the relatively low cost and high quality of the finished floor and the low cost of ongoing maintenance. We have found that when a polished concrete floor is properly finished at the outset, the floor’s appearance can be maintained by periodic cleaning and buffing with common janitorial pads under auto-scrubbing machines. We recommend using a neutral based cleaner. No harsh chemical cleaners or waxes are required. This saves the building owner a substantial cost over the life of the floor.
In high traffic areas, when refinishing is desired, it is usually possible to start at a mid-range grit and bring back the shine without going all the way down to a 40-grit tool.
We hope that this article has answered some of the common questions that flooring contractors face when thinking about polished concrete floors. Polished concrete can be a beautiful, cost effective and profitable alternative to traditional floor coverings and finishes. There is growing demand for polished concrete and the contractors that “do it right the first time” will capture more jobs with fewer call-backs. If you have additional questions, give us a call. We’re here to help.