A Foundation for Concrete Expectations

A Foundation for Concrete Expectations

By Kathy Danforth / Published April 2017


Monuments, statues, and historic buildings testify to concrete’s durability, so high-rise condominiums are often unpleasantly surprised by the necessity and magnitude of a concrete restoration project. Several factors compound the issue: the abundance of concrete in a high-rise building, the inability to precisely determine the extent of repairs in advance, the invasiveness of the project, its rather consequential expense, and in some cases a misunderstanding of the nature of concrete.

“In a condominium setting, concrete is everywhere,” observes Mariann Gerwig with Carousel Development & Restoration Inc. “It is used on decks, catwalks, balconies, pools, parking garages—anything to do with the structure of the condominium.”

Gerwig reports that 95 percent of their work is within a half mile of salt water, which is a clue to the main issue. “Moisture—in this case, salty water from humidity or precipitation—enters the concrete; the water evaporates, but the salt remains,” Gerwig explains. “An unexpected thing about concrete is that it is porous, even though it looks like a hard surface, so salt can enter. When the salt reaches the rebar, which is providing the structural support to the concrete, the rebar rusts. The rebar expands and fractures the concrete, which results in the condition called concrete spalling.

“This is why materials on top of concrete become so important,” Gerwig notes. “The worst thing you can do is install indoor-outdoor carpeting, which traps the water and salt underneath. Tile can also trap water if not installed properly. If tile installers don’t coat the entire tile, but just the corners to save on cost, it can trap water. Grout which is old and cracked will also allow water underneath. It is extremely important that all toppings on balconies be approved by the association.”

Problems can be caused by improper installation of railings. “If two unlike metals are touching, that will cause a chemical reaction and deterioration,” explains Gerwig. “This happens when railing screws touch rebar. So many times, we see aluminum railings where stainless steel screws have not been used to secure them to the slab.”

Pool decks are frequently elevated, and Gerwig comments, “When pool chemical rooms are under the pool, that can lead to problems. Evidently the chemical fumes can accelerate the rusting of rebar.”

Another problem is improper placement of the rebar during construction. “The rebar should be in the middle of the slab,” according to Gerwig. “Sometimes it is too high—an inch or so below the surface—so salt and moisture reach it much sooner.”

With a reconstruction project, the association can start afresh in preventing the next round of decay. “The composition of the concrete we use for our projects is a design mix that has rust inhibitors in it,” says Gerwig. “However, this is not used in new construction. The argument that can be made is that a large percent of the building is not exposed to the outside, so they don’t want to spend the extra money. However, there are times when the damage extends to the inside under sliding glass doors. In my opinion, considering the prices of oceanfront condominiums, it’s not that big of a difference in cost. They are in essence building our future work by not using corrosion inhibitors!”

Another variable in concrete composition is moisture. “The moisture level depends on how long the concrete will be in the truck,” says Gerwig. “Concrete has a life once it hits the truck, so a core sample from each load is tested for ‘slump,’ measuring the moisture, at the site, while other tests are performed at the lab. The concrete is tested after periods of time to ensure it reaches the required strength, usually 7,500 pounds per square inch (psi). That test is conducted at 7, 14, and 21 days, though usually it reaches required strength after seven days. Concrete will reach 90 percent of its strength in 21 days, but it will continue to harden for decades.

“We have never had concrete that did not reach the required strength,” recalls Gerwig, “but we have had trucks that had to leave. The pumping company actually contacts the concrete company and says when to send the concrete. We have had jobs requiring two trucks, and if the pumping equipment malfunctions and causes a delay, they have had to turn back the second truck because the concrete is beyond its useful life. The pumping company has to bear that expense, but it is minor compared to the expense of removing substandard concrete.”

To further protect concrete balconies and catwalks on buildings, a waterproof coating is usually applied. “The protection is different for exposed high-rise concrete, as waterproofing is not done on the concrete slab on the ground,” explains Gerwig. “We use the product specified by the engineer, normally a cementitious or urethane membrane. This is rolled or hand troweled on and cures. Both types will last a long time with proper maintenance, but urethane has a strong odor when applied, so most people opt for cementitious. The topcoat, a textured overlay, can be made to look like slate, tile, or a variety of materials.”

Gerwig recommends maintenance to preserve the concrete. “Regular painting is a basic maintenance item to protect the envelope of the building from water,” she stresses. “Water means damage. If there is not a maintenance department, it is highly recommended to hire a structural engineer to inspect the entire building at least every two years. You are looking for existing damage and any place water can enter the building. If shutters have been replaced, water can get in and enter the exterior walls if the screws were not installed with silicone.”

When obvious concrete damage is visible on the surface (beyond normal hairline cracks), it is considered spalling. Gerwig observes, “On walls or ceilings, it may just be stucco spalling and not concrete spalling. This has to be addressed, too, or water will get behind the stucco and cause damage.”

When repairs are recommended, an engineer may “sound” a balcony, listening for hollow areas needing repair. “Though the engineer estimates the work to be done, our contracts are unit price, so for every unit of repair we get paid. Ten years ago, just about every job was 30–40 percent over the estimated budget, with some much more. We concluded this was happening because engineers were conservative when they put together an initial budget. Today the engineers put together more realistic budgets and even build in contingencies. Contracts still go over but not as much as they used to. Often when contracts go over now, it may be due to change orders, such as adding new railings or other additional scope of work.”

An engineer will estimate the amount of concrete removal and replacement needed, but only when the concrete is removed and the rebar is exposed is the definitive amount known. “For a proper warranty, you must ‘chase the steel’—clean the rust off the rebar and expose two inches of clean, unrusted rebar,” explains Gerwig. “Also, if too much rebar has to be removed when the rust is being sanded off and it gets too thin, a new bar must be epoxied in next to the existing rebar so no strength is lost. The clean rebar is also coated with a rust inhibitor. If you do not get all the rust removed, the deterioration continues.”

Some communities decide to completely replace balconies when deterioration goes beyond a certain percent of the entire balcony. “It does cost more, but it’s a better end result,” observes Gerwig. “We won’t be back to those properties for many years.”

Concrete restoration is more intrusive than residents may anticipate, and for good reason: during the repair, they are not allowed access to many areas, and the work is loud and dusty. “Once the job is permitted as a construction site, we have total control for protection reasons,” advises Gerwig. “We do have the right to shut down the pool and tell people to stay off the balconies. We will not work on one balcony above another, and we use post shores on the two balconies underneath. Owners do not understand why they cannot use their balconies if we are not working on them. We need to explain that as long as we are working above their unit that concrete may fall and injure them. We have had people go out on a balcony above 20 stories high that had the railings removed, so at times we screw sliding glass doors closed. Unfortunately, managers often have to take the heat from the owners.

“Another major safety issue is working on columns in parking decks under a building,” Gerwig comments. “You cannot work on consecutive columns at the same time, and you cannot work on more than a fourth of an individual column at a time. If you do, you affect the integrity of the structure.

“Our warranty on concrete is five years, though if there is an installation problem, it will show up right away. The waterproofing products on top have manufacturers’ warranties for 10–15 years. They will send a maintenance schedule, and you have to substantiate that it is followed. However, since 1989 we have seen only one or two claims, which the manufacturers had to pay due to material failure.

“A number of jobs result from repair work not being done properly,” Gerwig relates. “Other trades without experience in the restoration field who have seen what is done think they can make the repairs, but if the repair is not done correctly or railings are done incorrectly, more work is needed. Often these companies will be out of business by that time. Concrete restoration is not cheap, but you want the best, not the cheapest,” advises Gerwig.

“It is surprising the number of condominiums without reserves for concrete restoration,” Gerwig observes, “It is a known repair at some point in time. Without reserves it has to be paid for by special assessment or loans. Broward County and south require an inspection for buildings more than 40 years old. If the structural engineering report recommends repairs, it has to be done. In one case, the city condemned a building, so everyone was going to have to move out. One of Carousel Development & Restoration Inc.’s owners went before the city explaining what the association had contracted with us to do, and the city allowed them to stay in the building until the repairs could be done.

“If the board realizes this is going to happen and sets aside money each month, it could avoid owners getting large assessments when the big project comes,” Gerwig advises. “Many restoration projects today incorporate sliding glass door replacement and railing replacement to give the building an updated appearance. All of this work adds to the value of the owners’ units.” Maintenance and regular inspections are the first lines of attack against deterioration of concrete, but realistic expectations also lay the foundation for concrete success.

Mariann Gerwig with Carousel Development & Restoration Inc. (CDRI) contributed to this article. For more information on CDRI, call (561) 272-3700 or visit www.CDRI.net.