Rescued!

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EDCO - Surface Preparation and Sawing Equipment > Expert Tips & Tricks > EDCO In Action > More Action Pictures > Rescued!

Rescued!

Murphy’s Law — whatever can go wrong probably will go wrong — is not cast in concrete or set in cement. In fact, it was temporarily repealed not too long ago when Creative Concrete and Restoration Inc. saved a botched concrete slab in Maryland.

Story By Jack Innis
Photos Courtesy of EDCO

Creative Concrete’s owner Gary Edwards was called in to look at an 85-yard slab poured a few weeks earlier at the Keymar Fertilizer Co.

What Edwards found was not good. “You could chip the concrete out with a car key to about 1/8 to 3/16 of an inch. Even the areas not flaking were chalking and dusty. You could sweep a section, remove the dust, sweep the section again and have the same amount of dust.”

While investigating the problem, Edwards learned that serious errors had occurred during the pour. The concrete crew was actually a handful of fertilizer employees working for the owner’s friend, who was the contractor. The owner pressured them to pour during a 100 degree day.

Then Murphy’s Law took over. The ride-on power trowel was put atop the matrix too early, sank and got stuck. By the time they dragged it out, they’d fallen seriously behind. The concrete was curing rapidly, so the crew added water to the surface and power troweled the best they could while the concrete set up.

A few weeks after it cured, more than 50 percent of the slab showed signs of spiderwebbing, cracking, and flaking between the cracks. Keymar was looking at about $50,000 to tear it out and repour.

“Before I bid, I told him I wanted to contact EDCO to figure out how much equipment I’d need to prep the slab. That would influence the costs,” said Edwards.

While EDCO is known as a surface preparation equipment manufacturer, the company is closely connected with rental yards throughout the nation and is considered an informational resource by many floor-coating specialists. EDCO sent out men and equipment to see what would work. They first tried an EDCO CD-5 Chip Dek Scabbler. These air-driven piston machines break up the concrete surface. “By regulating air pressure, you can take up just the bad and leave the good,” Edwards said. “But it’s relatively slow and leaves low areas that require filling with epoxy slurry. In this case I found it was cheaper to grind off a uniform layer and apply a thin layer of epoxy.”

To take off a uniform layer, Edwards chose an EDCO CPU-10C single disk 10” scarifier. The scarifier has rotating drums with carbide bits and acts like a planer to shave concrete with uniform consistency. It runs on 110 volts.

Prior to attacking the slab, Edwards adjusted the drum height by turning a small wheel on top of the machine. After making a test pass, Edwards began. “It’s a lot like cutting your lawn. You just have to keep it moving forward at about 10 feet per minute. If you push too fast you’ll feel resistance on the handles and begin missing stuff. But avoid going too slow. It’s easy to pause for a second and get too deep.”

The machine’s noise requires the use of earplugs at all times. Since the machine was connected to a dust vacuum in a well-ventilated area, masks were not required.

The next step was to knock down the ridges left by the scarifier with an EDCO Model 2-GC Dual Disc diamond grinder. “It works like a rotary floor polisher,” Edwards said. “You sweep it back and forth in about five-foot overlapping arcs and try to establish a rhythm.”

After grinding, Edwards and his crew swept the floor, then vacuumed with four Sears Craftsman 6.5 h.p. ShopVacs. With about 3/8-inch of bad slab removed and the prep behind him, Edwards layed down the first coat, Precision Epoxy Products’ FS-190 Epoxy.

First, he poured three gallons of the two-component epoxy, at a 2:1 mix ratio, into a five-gallon bucket and mixed for two minutes with a drill-mounted blade. Precision Epoxy advises against using solvent or thinner in this step.

“How much I mix at a time depends on how much labor I have,” Edwards said. “In this case there were three people, two to do the rolling and one to mix. I mixed all the epoxy for the whole project personally. (See “Sending a Rookie to Stir Paint is Asking for a Mix Up,” page 16.) The only thing you can do drastically wrong on this type of project is to mix incorrectly.”

With gloves, safety goggles, and respirators in place, the spreading crew used 18-inch Wooster Co., long-handled rollers with 1/2-inch nap to spread the epoxy. Edwards found that the men could spread a batch of epoxy in less than the 25-minute limit recommended in Precision’s product data sheet.

The goal of the rolling is to spread each gallon to cover about 160 square feet. “Using a 1/2-inch nap roller really puts you there,” Edwards said. “You can tell when you’ve got it right because the whole area looks good and the crevices look wet. We always eyeball things halfway through to see if we’re on track.”

Normally, a layer of 60 mesh sand is broadcast liberally into the FS-190 while it is leveling. The sand absorbs shocks caused when objects such as hammers are dropped and provides a slight amount of flex so the epoxy is less likely to crack in severe temperature swings, such as deep freezing. The sand is normally topped with another layer of FS-190, Edwards said. “Since the warehouse is not used for heavy, dense objects and is not located in a severe frost area, the owner decided to save money and forego the sand coat.”

After allowing the first coat to cure for a day, Edwards laid down the second coat, Precision Epoxy’s TC-200, a two-component, pure 100% solids, solvent free, pigmented system that is used as the two top coats of the three-step floor system.

After the TC-200 coat had been allowed to cure for a day, Edwards’ crew used a 20-grit sanding disc on a floor polisher to rough things up a bit. “In the summer, TC-200 will cure enough in one day to sand; in the winter, it might take three or four days. You can tell if you’re sanding too soon because you’ll get immediate clogging.”

After sanding, sweeping, and vacuuming, Edwards’ crew applied the final coat of TC-200 to achieve a 1/8th inch (125 mils) thick floor coating.

The resulting job saved the fertilizer company nearly $40,000 over the cost of having the slab dug up and repoured.

Edwards’ time spent finding the optimum surface preparation for the slab also led to the repeal of Murphy’s Law — at least until next time. CP

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