With concrete floors growing in popularity, you’re under more pressure than ever to produce a perfectly flat, smooth, and durable surface. Today’s thirsty mixes, however, make that harder than ever.
To keep concrete moist, some contractors add more water to mixes, spray fresh concrete with water, or incorrectly trowel in evaporation control products to help finish the surface. While these tricks for extending workability may initially work, adding water weakens the finished surface. The likelihood of shrinkage cracking, curling, dusting, spalling -- and unhappy customers -- increases.
Two companies have introduced products based on colloidal silica, a technology that they believe offers a better solution.
Introduced in 2012, Day1 from Solomon Colors Inc. in Springfield, Ill., is a liquid concentrate that’s mixed on-site or supplied ready-to-use. The other, introduced at 2014 World of Concrete, is MQ Whiteman SlabArmor from Multiquip Inc. in Carson, Calif., a two-product (Starter and Closer), two-step system that’s supplied ready to use.
Both Day1 and SlabArmor Starter are sprayed onto fresh concrete before and during troweling. Instead of water or evaporation retardant, the silica is a colloid: a solution of nanosized pozzolan particles suspended in liquid. When applied to the freshly placed slab, the solution reacts with lime in the cement paste, forming a silica compound that retains nearly all the surface moisture.
Because the silica is a pozzolan, it’s natural to concrete and doesn’t react adversely with other admixtures.
Solomon calls Day1 a “finishing aid”; Multiquip markets SlabArmor as a “multistep curing formula and application process.”
Although both products are reported to increase surface hardness and density, neither manufacturer classifies them as a traditional chemical surface hardener. And even though they minimize evaporation, both manufacturers distinguish their products from film-forming evaporation retardants.
Each manufacturer is targeting a different market for different reasons. As a result, there’s been some confusion about their intended use and benefits.
Solving color issues
Solomon Colors has sold iron oxide masonry and concrete pigments since 1927. The color supplier bought Lythic Solutions, which developed Day1, in 2013 to help contractors get better results with integrally colored concrete.
“One of the main problems we see with colored concrete is from botched finishing techniques; people add water to the surface, even put diesel on brooms,” says Business Development Director John Anderson. “Adding water not only affects color quality, you can also end up with a lot of dusting and spalling.”
Solomon wanted to offer an alternative that encourages better finishing practices and improves surface quality for colored and decorative concrete.
Supplied as a liquid concentrate mixed with water at the jobsite or in the ready-to-use formula, the product is sprayed on fresh concrete during placement and finishing. Designed to be floated or troweled into the surface, it can be applied multiple times as needed during the finishing stages, as long as the total of 250 square feet per gallon per application is not exceeded.
“A lot of our after-treatments, such as acid stains and surface deactivators for exposed aggregate concrete, react with free lime at the surface. Because of that, you can get a lot of variation in the surface appearance from light tones to dark tones or with aggregate exposure when using surface deactivators,” says Anderson. “Using colloidal silica evens out the free limes [and helps produce] good color consistency with stains and depth of aggregate exposure, even on gray concrete.”
Click here to watch a demonstration from 2013 World of Concrete.
“Some people have the misconception that these products retard the concrete, but that’s not it,” says SlabArmor Product Manager Ben Wiese. “Instead, they keep the surface area very evenly hydrated.”
Adapting to power trowels
Power trowels are one of the many products that Multiquip makes, so developing SlabArmor was a logical next step for offering customers a turnkey finishing solution.
Mixes consume water much faster than they used to as water-cement ratios are much lower to achieve higher early strength and durability. By mechanizing the finishing process, power trowels enable contractors to cover more ground more quickly. Both of these advances increase productivity, but they also mean contractors are constantly chasing a drying surface.
Troweling squeezes water out of concrete via increasing pressure applied over multiple passes. Depending on specifications for flatness and hardness, five or 10 passes may be required. If the surface dries too quickly, during finishing it can be closed too soon and isn't properly dewatered and consolidated because of the lack of surface moisture.
The SlabArmor system consists of two products -- Starter and Closer -- applied in two steps.
Starter is hydrophilic, which means it combines with the water in the concrete mix. It’s sprayed on fresh concrete in three equal applications at a rate of 1,200 square feet per gallon once before bull floating and two more times during troweling.
After that, Closer is spray-applied and left on. Described as a “spray-on condensifier” that dust-proofs and hardens the concrete, the liquid is hydrophobic, which means it repels water.
“Starter's neutral-pH silica creates a reaction that drives down into the concrete capillaries and blocks these evaporation channels,” says Wiese. “That allows you to finish the concrete with the water that’s already there. Closer locks the surface up to maintain the internal moisture, and also densifies and hardens that surface.
“When the contractor walks away, no one needs to come back and put anything else on that slab. It’s ready for polishing or heavy industrial traffic.
“The chemistry has finally caught up with the equipment and mixes. This product gives contractors time to finish concrete properly.”
Click here to watch a demonstration from 2016 World of Concrete.
In addition to easing the finishing process, the products are said to increase concrete’s abrasion resistance, impact resistance, and surface compressive strength.
Not film formers
Both manufacturers emphasize that these products differ from film-forming evaporation retardants like AquaFilm and Confilm, which some contractors use to keep the surface wet during finishing.
“Evaporation control products aren’t meant to be used as finishing aids,” says Solomon’s Anderson. “They can only be applied between passes. They’re designed to act as a temporary vapor barrier to keep moisture from migrating out of the slab for 20 minutes to 30 minutes under hot, windy conditions. After that, you can trowel in the film, but you should never trowel it in its wet form.
“Some finishers will tell you they’ve been using Confilm [that way] for 20 years without a problem, and that’s true on the day they’re finishing the slab. But if you come back six months or a year later, you’ll find severe dusting and micro-pits, usually after the first freeze-thaw.”
Bob Harris, a senior decorative concrete consultant with Structural Services Inc. (SSI), has tested both products and is pleased with their performance.
“We sprayed a slab with Day1 four times during the finishing process,” he says. “I was afraid it would discolor, but it produced a consistent, homogeneous color.
“We tested the SlabArmor on an interior slab. The day after installation, the surface seemed harder than normal. I got a result of 6.5 or 7 on a Mohs surface scratch test 24 hours after placement, which is an indicator of very hard concrete.”
SSI consultant Denny Bartz used SlabArmor in a Florida grocery store in the summer of 2015.
“We did one application of Starter at strike-off, then two more applications while panning the floor,” he says. “We applied the Closer later the same day. It’s an exposed concrete floor, not polished but just high-speed burnished.
“We’ve gone back a few times to check on and test it, and it seems to be holding up well. One of my partners visited a week or two ago and says the store manager is really happy with the way it cleans up.”
Whether you’re finishing by hand or power trowel, it may pay to give these products a shot.