Putting On A Beautiful Face: New-Generation Patching Compounds Help Meet The Demands of Fine Architecture
By: Michael Chusid, RA FCSI ACI and Steven H. Miller
Tilt-Up has become an architecturally sophisticated form of construction, and finishing methods have matured with it. Few contractors still use the old-fashioned method of sand-and-cement sacking. Most have switched to specialized patching compounds.
But when a new material is put into a craftsman’s hands, unexpected things happen. The new-generation patching compounds are inspiring creativity. Instead of just smoothing rough spots and bugholes as preparation for painting, these products are being used as exposed finishes. They are becoming vital tools in the growth of the “concrete aesthetic” as more architects specify exposed concrete – but without the flaws. Some applicators are also exploring new territory with the use of color and special techniques.
BEAUTY IS SKIN DEEP
Tilt-Up started off plain and utilitarian, but it’s grown up into something that architects use to create beauty. These buildings need to look good at close range. As this trend arose, contractors found that the methods they’d used for decades were no longer acceptable to architects and owners. Sand-and-cement sacking could not produce a smooth enough patch to get approval, even after it was covered with paint.
Contractors tried alternative materials. Gypsum-based drywall compound, however, was not durable enough, and epoxy was not workable. Tilt-Up needed specialized materials, designed to give better results under real-life jobsite conditions.
Cement manufacturers began to offer new compounds. Although a few of their premixed patching materials are still designed for dusting – basically just packaged versions of the old-fashioned sacking method – the majority are one-component premixes designed to be trowel-applied. The new method is considerably faster and more productive. Both mixing and application are accelerated. It is less tiring for workers, so productivity remains high day after day. Eliminating the loose sand and powder released by rubbing techniques is healthier for workers. It is also less wasteful of materials, and eliminates the costly damage of sand getting into lift machinery controls.
Since the new materials were developed, the level of finish quality has continued to rise. Architects are even specifying exposed concrete Tilt-Up buildings. This actually complicates finishing, because the Tilt-Up casting process still produces flaws that are not necessarily part of the architect’s vision. The blemishes have to be fixed, but in a way that blends in completely and doesn’t compromise the ‘concrete look.’
THE NEW ALTERNATIVES
Some features of the new products are similar: they tend to be single component, trowel-applied, and fairly fast-setting. They are developed for strong adhesion. They all advertise smooth finishes and application down to featheredge thinness. However, applicators say there are some distinct differences between products. Of the major brands that publish their ingredients, most are made with “graded silica aggregate” or “graded aggregate” (i.e. sand), a material that puts a hard limit on the smoothness of texture that is achievable. One product advertises a finely ground sandable aggregate, and applicators report that it can produce a finish almost as smooth as glass.
According to Matt Sambol, Product Development Engineer for Rapid Set WunderFixx at CTS Cement Mfg, Cypress, CA, contractors are very specific about the properties of a patching compound that produce fine finishes and good working conditions. “They want a smooth mixture with absolutely no gritty feel and a buttery consistency for a true feather-edge application,” explains Sambol. “It should be rapid-setting, sandable, paintable the same day or the next day at the latest, and durable over the long run. They want a color that matches natural concrete, but it should also be compatible with pigments for doing integral color finishes.”
Ron Drennan, a veteran sacking contractor in Southern California who is currently General Manager of Restoration Concrete, Long Beach, CA, took part in the development of Sambol’s product. He recalls working for five or six months with different formulations, bluntly critiquing the results and helping the engineers understand the real-world challenges. Drennan believes that field testing is vital to the development of a good product, because the constantly changing conditions of the jobsite can’t be matched in the laboratory.
“There’s gusts blowing,” he explains, “One minute it’s cloudy and half an hour later there’s sun and it’s 90 degrees. The product reacts differently than it does in a lab environment.” Drennan’s company has switched entirely to the new methods. The results they achieve have won two TCA Achievement Awards that specifically cite the finish as a significant element of the achievement.
Drennan had one misgiving about the development process. “My company has always had an edge because we had expert craftsmen,” he explains. “I knew that once this product was developed, it would level the playing field, because almost anybody can use it. That’s exactly what’s happened. I said at the time, this is going to change the nature of our whole business, and it has.”
Ardex Tilt Wall Patch and Rapid Set WunderFixx were among the first products on the market. Numerous others have emerged including Lyons Mfg Patchcrete and Pavecrete, Euclid Chemicals Tammscrete, W. R. Meadows Speed Crete, and Noxcrete Panel Patch.
Today, Drennan and his team are sacking the largest construction project in California, the massive Stater Bros. Distribution Center in San Bernardino. Among the numerous structures in the complex are a 1.45 million square foot warehouse with 40-foot high walls, a .5 million square foot refrigerated warehouse, and a 1.25-mile long screen wall. Drennan’s team is sacking all of it, keeping 11 lifts busy. If a project this size were sacked with sand-and-cement, especially in this rather breezy location, the wind-borne dust could become a significant source of pollution of the local environment. With the trowel-applied compound, the jobsite is clean and so are the workers.
Even though the walls at Stater Bros. are being painted, the smoothness of the sacking has been noticed, and it’s set the standard for all concrete on the project: a precaster was forced to redo a set of columns for the site’s corporate office building so they matched the quality of the sacking.
PERFECTING THE INDUSTRIAL LOOK
Elsewhere in California, a Tilt-Up house just won a 2008 TCA Achievement Award, given in part for the excellence of the finish. The Rod and Debbie O’Connor residence in Anaheim Hills is a 7,200 square foot, two-story structure, a rare instance of Tilt-Up used for a single family home. The exterior features a mix of painted concrete and stone veneer, with several exposed concrete columns flanking the entrance. Inside, the owners wanted to create an industrial look, and intended to leave all the concrete on the interior side of their Tilt-Up walls exposed.
Because of the fairly small footprint of the house, some walls had to be cast stacked on top of other walls, resulting in damage to the top side of some panels – the side that would become exposed concrete interior surfaces.
“Some of the walls were just too messed up to be left raw,” explains Debbie O’Connor, who acted as interior designer for her home. They engaged Restoration Concrete to bring the finish up to their standards.
Chuck DeGrood, one of Restoration’s most experienced craftsmen, was able to skim-coat damaged walls so skillfully that they match adjacent hard-troweled raw concrete. De Grood tinted the patching compound to match the concrete color. “I applied the compound and let it set up. Then hard-troweling it got it burned in and gave it an almost marbleized look.”
“One of the cool things,” comments Debbie O’Connor, “is where there are two walls adjoining: one is patched, one isn’t, and you really can’t tell the difference.” The exposed concrete is about equally split between patched and raw surfaces.
Their second-story covered deck is an indoor/outdoor room. One wall is actually concrete, but the ceiling and opposite wall are frame construction dry-walled with cement-board. De Grood was able to skim-coat the cement board to look like concrete, unifying the room.
Regarding the finishing, TCA’s Achievement Award citation stated, “The easy application of Rapid Set WunderFixx allowed for an exceptional finish. WunderFixx was utilized to treat the majority of the exterior surface. Because many of the interior concrete walls were left unpainted, WunderFixx was used to maintain an unseen transition from the raw panels to the patched surface.”
INVISIBLE FINISHING
In St. Lucie, FL, about a hundred miles north of Miami, Tilt-Up contractor Sunshine Structures met an even more demanding challenge using one of the new patching materials. The Havert L. Fenn Center, St. Lucie, is a large gymnasium-type building designed as a special needs hurricane shelter. Although most of the building is texture-coated, the architect wanted one 80 x 34 foot wall along a walkway left as exposed concrete … exposed, but without bugholes or other imperfections.
Architect Johnnie Lohrum of Schenkel Shultz Architecture, West Palm Beach, FL, explains that the designers sought a natural look for that wall. “We wanted to create an entry way, bringing the adjoining park into the building.”
“Trying to meet their expectations on this took a while,” says Gabriel Reyes, General Superintendent for Sunshine’s East Coast operations. “We tried a lot of different materials, but they were all rejected. There was too much grit in them. You would pass the trowel over it and it would look like you were sanding with a heavy grit sandpaper. We finally tried WunderFixx, and that was it. We put it on so thin, you can actually see the concrete panel, with a light sheen of compound over it. It covered the imperfections but still gave it that shadowy look of the concrete itself. You couldn’t do that with any other material. There’s very faint surface texture, and that’s what we were looking for.”
Of the troweled finish, Lohrum comments, “I specified a rubbed-off look, and I got the look I wanted. It really looked like exposed concrete. I think you would never know there’s a topping on it. I’m very happy with the result.”
COLOR IT SMOOTH
St. Louis-area sacking and patching specialist Josh Hric, who works for Ahal Contracting Co, Bridgeton, MO, has been creative and managed even more unusual results. In one instance, he applied a wet mix of WunderFixx with a paint roller. “We rolled it on an interior wall at St. Louis University Research Center, filling bugholes. Then we troweled it out. It was as smooth or smoother than drywall. Actually, it looked like a sheet of glass.”
Hric was brought in on another project, a problem with a waterfall fountain: the texture of the plain concrete was causing splashing. He was able to apply patching compound so smooth that it reduced the friction between concrete and water, eliminating the splashing problem.
“Since I started using it,” reports Hric, “they call me The Magician.”
Ahal, one of the largest Tilt-Up contractors in the Midwest, switched all patching away from rubbed-on materials to a new-generation patching compound in 2006. Foreman Bryan Costello reports that it is twice as fast. He also cites the elimination of dust as a major advantage.
Costello, too, has gone into new territory with the material. He has added pigment to the patching compound for a variety of projects, including finishing panels that were cast with brick-texture form liners.
He recalls one particular project that brought out unusual creativity in the use of color. To refurbish a concrete dugout on a baseball field, they first coated it with a rapid-setting mortar mix. Then, they mixed blue pigment into a very fine-grained patching compound and skim-coated the entire surface. While the compound was still wet, they loaded a pounce pad with dry pigment and dusted the surface, creating a dark- blue mottled effect. “It gives it an ocean kind of look,” comments Costello.
Undoubtedly, these innovative uses are just the beginning. As more applicators try the materials, and more demanding projects come to Tilt-Up, new ground will continue to be broken.
