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Self-Leveling Toppings
In a Hurry? Preparation and Timing are Everything with Fast-Drying Self-Leveling Toppings
by Susan Brimo-Cox
As with other concrete projects, preparation is the key when using fast-drying, self-leveling toppings. Even if you don’t see a lot of problems with the substrate, don’t skimp!
“Prep is 90 percent of the job [and] you’re only as good as your prep,” says Richard Smith, president of Richard Smith Custom Concrete in West Hills, California.
Shot blasting is the No. 1 method recommended by fast-drying, self-leveling product manufacturers and contractors alike. Use grinders for the hard to reach edges. But when you’re done, be sure to get up all the particles and dust.
“From prep to sealing — no dust!” cautions Peter Golter, product manager for MAPEI in Deerfield, Florida. “You don’t want primer sticking to concrete dust or drywall dust instead of having direct contact with the substrate. Same for the sealer; if there’s dust on the topping, it’ll be a rough topping and the sealer may delaminate.”
After shot blasting, Smith patches and repairs the substrate where needed then applies the primer, which he typically lets cure a little longer than what’s required. “What troubleshoots cracks and failures,” he says, “is the preparation.”
The substrate preparation and primer give you the benefit of two bonds for the topping, observes Fabyonic. “Shot blasting profiles the substrate for a physical (mechanical) bond. You achieve a chemical bond through the use of primer.”
Follow the manufacturer’s directions for the primer. The mix ratio, recommended number of coats and dry times differ among products. Applying the primer with a broom ensures the primer is worked into all the nooks and crannies of the substrate. And be sure to completely cover the surface. Not only won’t you get the desired chemical bonding on those unprimed spots, they also will allow air to come up from the substrate and create pinholes in the topping, which can become an aesthetic problem.
This part of the job needs to be planned out perfectly.
“Have your mixing area ready, bags ready and have one guy mixing while the other installs,” recommends Ron Garamendi of Recreation Development Co. in North Las Vegas, Nevada. In addition, “you have to be careful you don’t work an area too big.”
What’s the big deal? The “fast-drying” properties of the products mean you have mere minutes of working time. At 70 degrees Fahrenheit and 50 percent relative humidity, you have about 10 minutes before the topping begins to gel. The hotter the temperature; the less working time you have. The minimum recommended temperature of the substrate for application is 50 degrees.
Don’t neglect considering the temperature of the topping materials, either. Preconditioned material is important. In the wintertime, make sure you’re using products at room temperature.
When pouring fast-drying, self-leveling toppings, one-quarter-inch is the minimum thickness recommended and 2 inches is the maximum. A thicker pour does not increase performance. Also, if a thicker application is required these toppings may not be the most cost-effective products to use.
At the time of application, “turn off the air conditioning, heat and avoid direct sunlight where you pour,” advises Golter. “Airflow will cause ripples, which can crack and it’ll look like a dried mud bed.”
Another cardinal rule: Honor expansion joints throughout the process. “For saw-cut control joints, you can self-level over them, but map them in and make saw cuts in the topping to mirror them,” says Fabyonic.
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