If you know the air temperature, relative humidity, concrete temperature and wind velocity, you can determine the potential for surface crusting using this nomograph.
Photo credit: Steven Kosmatka and Michelle Wilson, Design and Control of Concrete Mixtures. Portland Cement Association, 2011. p.323
The Kestrel 4300 construction weather tracker measures ambient weather conditions and the temperature of concrete to compute surface crusting conditions using the nomograph formula.
Photo credit: Joe Nasvik
The RH sensor (left) is inserted permanently into a drilled hole in a floor slab. The reusable reader (right) is inserted into the probe to read the RH and temperature of the slab.
Photo credit: Joe Nasvik
To determine how hard a floor is using a Moh's hardness pick set you scratch the surface with each pick, starting with the lowest number, until you see a scratch. This helps you select the proper diamond pads for polishing operations.
Photo credit: Mineral Labs
Contractors helped HTC develop the Standup Edger for polishing floor edges and hard-to-reach places.
Photo credit: HTC
Both polishing contractors and owners are buying gloss meters to check the level of gloss finish required for an installation.
Photo credit: Horiba
Contractors and owners are also buying slip resistance meters. Contractors use them to be sure their work isn’t too slippery and owners measure their floors at regular intervals to minimize the risk of customers falling.
Photo credit: Regan Scientific Instruments
Fairly new to the marketplace, three-plane lasers are fast and accurate. One feature is the ability to establish square corners, making layout very easy.
Photo credit: Bosch
Increased power and run time make battery powered circular saws a way to increase productivity on jobsites. They are very portable and save the cost of moving generators and cords around a jobsite. Both 18- and 36-volt tools are used.
Photo credit: Bosch
Twelve-volt impact drivers can fit into tight places and you can carry them in your back pocket.
Keeping up with tool technology is important. Tools make jobs easier, increase productivity and make it possible to do more than you could do without them. Tools help you be more productive, understand conditions around you, install work to a higher degree of accuracy and verify results to assure all parties that work was properly installed.
Here are some tools to consider purchasing for your decorative concrete business.
1 Managing the weather
Weather and its consequences can be very expensive to contractors. Good forecasting is one way to limit your exposure, but forecasts may originate at reporting stations located several miles from your project. Nielsen-Kellerman (NK), the manufacturer of Kestrel Weather & Environmental Meters, offers the 4300 Construction Weather Tracker, developed just for the concrete industry. It reports jobsite weather and predicts when surface crusting conditions are present.
Kestrel weather meters are hand-held and weigh only a few ounces. They report wind speed, temperature and relative humidity. The 4300 uses the temperature of the concrete (which you input) and calculates the rate of evaporation of surface moisture, letting you know if there is a potential for surface crusting. Knowing this beforehand affords the opportunity to decide which preventive measures to use.
Deriving the formula to calculate the evaporation rate of water dates back to 1952. In 1960 the National Ready Mix Concrete Association (NRMCA) used the formula to create a nomograph to plot the rate of evaporation of a fresh concrete surface when ambient temperature, relative humidity (RH), concrete temperature and wind speed are known. The Kestrel 4300 automatically does the math for you. A number of 0.20 or higher indicates surface crusting is present. Many overlay cement products, coatings and sealers state the weather conditions they must have.
2 Monitoring the moisture content of concrete
Some decorative concrete products are very sensitive to moisture levels in concrete so you must measure the relative humidity (RH) of a slab to know when to install them. There are a few manufacturers that make this easy and affordable with a one-time-use moisture probe, but following the correct protocol is important.
Jason Spangler of Wagner Meters, which manufacturers the Rapid RH moisture probe, says sensors should be installed no sooner than 28 days (preferably more) after concrete placement. To get an accurate reading, the new ASTM F 2170-11 guidelines require you to drill a hole in slabs, which are dry on one side, to 40 percent of its thickness. For example, if a slab-on-grade is 6 inches thick, the hole should be drilled 2.4 inches deep. The hole must be perpendicular to the surface, straight and round. Afterwards the hole must be thoroughly cleaned before the sensor is placed at the bottom of the hole.
The current ASTM standard requires all manufacturers’ RH probes or sensors to be positioned the same distance from the bottom of the hole (no more than .625 inches) to ensure all readings, regardless of the manufacturer, will be the same. Wagner makes this easy because you push the sensor as far into the hole as it will go. The sensors are a single-use type so there is no need to continually verify the calibrations ASTM F 2170-11 requires for other types of reusable probes. A “reader,” which can be used repeatedly, is inserted into the hole to acquire the readings from sensors. Decorative floor finishes each have their own RH requirements.
3 How hard is your concrete?
It’s important for diamond polishing contractors to know how hard concrete floors are before starting work. Diamond pad manufactures now design pads for different concrete hardness applications for each grit size. If you don’t use pads designed for the right concrete hardness you could waste time and money. So a scratch test system has been devised based on the Mohs’ hardness scale — originally used to measure the hardness of stone, but it works for concrete too.
Today, test kits are available consisting of numbered “picks.” Each number is related to a Moh’s hardness rating. You start by scratching the floor surface with the lowest number pick and continue up the scale until you see the first signs of a scratch in the concrete. This pick number tells what series of diamond pads to use for the polishing process.
4 Polishing the edge
Clif Rawlings, product manager/training coordinator for HTC America, says it’s always been easier to diamond polish the center of a floor than its edges. So with the help of polishing contractors HTC designed the HTC 270 EG “Standup Edger” to efficiently perform work along the edges.
The tool features an 11-inch-diameter polishing pad, mounted on an adjustable grinding head only 412 inches high and 10 inches deep, allowing it to fit under kick-tow plates, coolers, racks or even shelving in retail space. The wheels of the 230-pound machine freely move on the floor while the head of the machine can be tilted to the contour of the floor and rotated to the left, center or right to grind against walls. The grinder shroud has adjustable wheels which run against verticals to guide the machine, allowing easy operation.
5 Measuring gloss
In the past, diamond polished floors were specified to be polished to a designated grit level. But owners wanted their floors to have a uniform glossy appearance because customers like glossy floors. So gloss meters have become a popular tool for both contractors and owners representatives. Using products like the Horiba IG-331 Gloss Meter, contractors can measure gloss as they work. This instrument measures 60 degree (most commonly used) or 20 degree angles (for very high gloss requirements).
6 Measuring slip resistance
Sealers, coatings or diamond polished finishes can increase the risk for pedestrian slipping and falling. To ensure public safety, owners and contractors measure slip resistance with tools like the RSI BOT-3000 made by Regan Scientific Instruments (RSI). The company’s president, Peter Ermish, says the generic name for these instruments is “tribometers.” They measure the coefficient of friction (traction) between two surfaces rubbed together — the higher the coefficient of friction, the higher the slip resistance. The BOT-3000 is about the size of a shoe box and has interchangeable rubber or leather sensors (simulating shoe surfaces) that pass over wet soapy floor surfaces during the test. The ideal reading for diamond polished floors is 0.42; below 0.30 is considered unsafe. Ermish says most of their sales are direct but some diamond polishing manufacturers also sell them.
Forming and bulk-heading
The ongoing development of cordless tools using lithium (LI) battery technology makes them more indispensable. They have increased run time and are more powerful, at the same time weighing less and becoming smaller. Here are three tools for building formwork to make your work easier and more accurate.
7 Three-plane lasers
With this small tool you can set elevation, plumb and lay out square corners. For indoor work the Bosch GLL 3-80 projects a red laser line visible for approximately 30 feet. Set the tool in pulse mode for long range commercial interior applications and small exterior applications and a receiver-sensor picks up the signal up to 265 feet away. The tool also self levels within a couple of seconds and can be used for laying out lines and setting points.
8 Impact drivers
For many good reasons, contractors are converting from nails to screws for setting forms. The advent of impact drivers is part of the reason because they make it very easy to drive screws. The most popular models use 12- or 18-volt platforms. Twelve-volt impact drivers are small enough to fit in your pocket and can drive screws in spaces as small as 512 inches. Eighteen-volt models drive screws much faster with more force.
Impact drivers use hammer and anvil systems that strike each other twice in every rotation, driving the screw. This movement also causes the bit to re-seat itself into the head of the screw as it turns. As a result it takes very little energy to use the tool compared to a conventional drill driver. A prime advantage of impact drivers is their size because they can be built smaller than drill drivers. They are faster, too, as much as 40 to 50 percent.
9 Circular saws
Using a cordless saw allows one to easily move to any location on a jobsite and battery technology improvements have greatly increased run-time and power between charges. The most popular platform is 18 volts, but 36-volt saws provide more power. However, recent changes in 18-volt batteries are catching up to 36-volt platforms.
Advancing technology in the construction industry is changing everything today. It’s important for you to keep up with this so you can become a more productive worker.
Joe Nasvik is a writer and editor serving the concrete industry. He has 18 years experience as a concrete contractor. Contact him at firstname.lastname@example.org.