By Kathy Danforth / Published February 2016
The connotations of concrete are strength, permanence, and solidity. The reality of concrete in balconies is that the integrity of the combination of concrete and steel is most often degraded by that seemingly innocuous foe: water. As water evaporates and salt is absorbed into the concrete, the rebar rusts and expands up to several times its original size, thus exerting internal pressure, which causes cracks and spalling concrete.
“The causes of concrete deterioration can act independently or together,” advises William Pyznar, principal engineer with The Falcon Group. “Original construction defects, such as use of an improper type of concrete, use of rebar, which already has corrosion, or improper placement of the materials, will accelerate the process. The reinforcement steel requires a certain amount of coverage, so if there is not enough concrete on top, salt and water will reach the steel earlier, leading to cracks and spalls. The concrete also shrinks as it cures, so you need proper reinforcement and curing techniques to control the amount of shrinkage and appropriately-spaced joints to allow for future expansion and contraction.”
Despite its tough image, proper pouring of concrete is a surprisingly delicate operation. “There are a number of things you can do wrong in terms of weather, mixing, or placement,” comments Pyznar. “If it sits in the truck too long and they add water to make it workable again, that will affect the quality and durability. The weather during construction is also a factor—you have to avoid drying the concrete too quickly in hot weather, as well as having too little or too much water.” The coastal environment also comes into play, according to Pyznar. “Salt is blown onto the concrete, and when rain hits, it makes a brine solution that penetrates through the cracks resulting from the expansion and contraction due to temperature changes and other external forces.”
Loading and additions to the balcony can also lead to deterioration. “The structure is designed for a certain weight, so if someone puts a hot tub on the balcony, that can cause failure. Tile, which is improperly installed, or outdoor carpeting can hold water underneath and accelerate water penetration and corrosion,” says Pyznar.
Other construction aspects can contribute to early deterioration. “The balcony should slope 1/8–1/4 inch per foot so it sheds water, and rain does not puddle and soak in,” observes Pyznar. “Locations where railing posts are connected are very important; they can be surface mounted or connected with a post pocket and sealed around that. When the aluminum post expands and contracts at the pocket, we often see spalls. Sliding glass doors and the flashing where the walls meet the balcony have to be considered. A curb three to four inches above the balcony is needed at doors so rain is not blown in, but that is not always present.”
Mariann Gerwig with Carousel Development and Restoration, Inc. advises associations to watch for any signs of concrete spalling (deterioration), lifting tile due to deteriorating concrete, or rust spots. She states, “Seemingly insignificant problems on a building’s surface may be outward indications of much more serious problems beneath that can only be determined by a qualified, experienced structural engineer.”
Steven Mainardi, P. E., with Delta Engineering and Inspection, notes, “If spalling in balconies or other concrete components is not addressed in a timely manner, the consequences can be great. Once the corrosion process of the embedded metal reinforcement has started, the spalling of the concrete will continue, leading to further concrete distress and damage. This potentially will result in the expansion of the repair boundaries and ultimately a reduction in the overall load-carrying capacity of the structural element. It is critical that repairs are made to minimize overall repair costs and to preserve the structural integrity of the concrete component. These conditions, if neglected, have the potential to cause structural failures and collapse in extreme cases.”
Inspections should be performed every few years, but a condition assessment is necessary to determine what restoration/maintenance steps are needed when deterioration has begun. Mainardi explains, “A condition assessment of the balconies is conducted by engineering firms specializing in the field of concrete restoration and typically includes the engineer’s review of the original structural plans and prior exploratory reports; visual observations of the balcony to assess the existing condition of the concrete surfaces with the intent to identify areas of distress; and acoustical emission testing or sounding of the concrete surfaces with light-weight hammers, chains, or other detection tools to detect hollow-sounding profiles typically associated with debonded and spalling concrete. When striking areas of concrete, a distinctly different sound is audible when crossing over debonded areas. In certain instances, additional inspection and engineering tasks may be employed, which include but are not limited to crack and damage mapping of the balcony, which diagrams the areas of spalling, cracks, and distress; core sampling of the concrete for testing to determine the compressive strength, pH, chlorides, and carbonation of the existing concrete; the use of a covermeter or pachometer to determine the location of the steel reinforcing and depth of concrete coverage; and half-cell potential testing.”
Gerwig points out, “There is no known method of inspection that can ‘see’ the full extent of the deterioration until the concrete is actually chipped open to expose the amount of deterioration of the reinforcing steel inside the concrete. We have found areas that show all the signs that they will require extensive repairs turn out to be in pretty good condition and, conversely, areas that appear to be very good end up needing a great deal of repairs. Because the full extent and scope of the work cannot be known beforehand, yet must be completed to rigid standards, the actual quantity of repairs often exceeds the estimates. Many engineers recommend that associations budget a contingency of about 25 percent.”
“If the association limits the study and says, ‘Just do what needs to be done,’ there will be more variability in the budget,” comments Pyznar. “The more you know, the more accurate the budget will be. With a full assessment, a restoration project should be within 10–15 percent of the projection. Accuracy also depends on engineering experience based on how much corrosion is typically found beyond the actual amount identified.
“With an older building that is dated in appearance, a balcony project may be the time to replace railings and improve aesthetics with coatings and colors,” notes Pyznar. “New coatings and railings may improve curb appeal and unit values.” Gerwig concurs and points out that this would also be the time to replace sliding glass doors and shutters, if desired.
Repair may involve a combination of removal and replacement of concrete; cleaning, coating, or replacing rebar; replacing expansion joints, and applying sealants, coating, corrosion inhibitors, and waterproofing membranes. Mainardi explains, “The International Concrete Repair Institute (ICRI) and the American Concrete Institute (ACI) provide the leading standards and guidelines related to the repair of concrete. The boundaries of the repair are determined by the extent of concrete damage and the limits of the corroded reinforcing steel within the concrete. In general, these standards employ the basic fundamentals of removing the distressed concrete in regular-shaped patterns with 90 degree cuts around the limits of the repair. Spalled, loose, and distressed concrete is removed from the areas as well as from around the reinforcing steel. The reinforcing steel is cleaned of rust and scale and coated with a corrosion inhibitor or scrub coat. Conventional concrete repair methodologies using non-polymer-modified or polymer-modified mortars are typically the norm for the repair of concrete balconies in condominiums. These methods employ the use of corrosion-inhibiting agents applied to the reinforcing steel and the re-pouring of the damaged area with a cementitious mortar. Surface penetrating corrosion inhibitors and waterproofing membranes are also utilized in some instances, particularly when concrete coverage is a concern. These are designed to penetrate the bare surface of the concrete and diffuse, in vapor or liquid form, into the steel reinforcing bars embedded in the concrete.”
Diverting the corrosion process to a more attractive target is a newer option, according to Mainardi. “Gaining in popularity is the use of galvanic corrosion protection, which does not require an external power supply, but rather involves the use of embedded galvanic anodes,” he shares. “These anodes traditionally are approximately the size of hockey pucks, but now come in many configurations and sizes and are embedded along the rebar grid. Once installed, the zinc core within the anode corrodes preferentially to the surrounding rebar, thereby providing galvanic corrosion protection to the reinforcing steel.” Cathodic protection, which requires an external power supply and diligent monitoring, is a costly option, which is not universally accepted for condominium restoration.
“The type of structure has to be considered as well,” Pyznar notes. “Some steel and concrete forms are precast in a factory under more controlled conditions and then put together with cranes, while other construction is cast in place. Post-tension construction enables thinner slab structures and uses slabs with a hollow core that have steel tendons installed once they are in place. Failure at the post pocket of these can cause catastrophic failure, so it is important to understand the type of structure you are looking at.”
Following the assessment, the engineer will draw up plans and specifications, procure bids and assist with their review, and typically oversee the actual project. Gerwig advises, “Since the building departments are not equipped or willing to perform the inspections on a restoration project (because of the use of swing stages and mast climbers on multi-story buildings), the structural engineer must also be qualified as a threshold inspector. This allows the engineer to submit a special inspector’s letter with the permit application, act as the inspector, and send inspection reports to the building department as the job progresses.”
Gerwig observes, “While the engineer’s opinions regarding bids and contractors are important, it is ultimately the board that hires and must get along with the contractor. Usually three contractors are selected for in-depth interviews. This gives the board an opportunity to discuss the bid, the project schedule, and the manpower and equipment that will be used. It is also very important to find out more about the contractor’s experience and the management team that will be involved with the project on site or off site. The key to a successful project is communication between all parties, and the interview will give the board members a sense of how comfortable they feel communicating with the contractor and its project team.”
Because of the uncertainty in knowing the actual amount of damage until the concrete is removed, Gerwig states, “A standard stipulated sum contract simply does not work for concrete restoration projects. A ‘unit cost’ contract has become the standard contract and billing format, with the owner paying only for repairs actually completed based on square footage, linear footage, or cubic footage of concrete.” Though some associations request the contract be sent directly to the board, Gerwig observes, “If the association’s attorney will be ultimately reviewing the contract, it actually saves time to have them involved from the beginning. Otherwise, the contract is negotiated between the association and contractor, and then the attorneys do it all over again.”
“During the project, the engineer typically acts as the owner’s representative,” explains Pyznar. “We mark the areas of concrete to be removed and inspect materials, mixing, application, and curing. Since there were unknown quantities of materials, we verify and approve quantities and invoices for the association.”
Gerwig notes, “Testing of repaired concrete is also performed by an independent testing firm to ensure that the concrete has reached its required strength before additional work can be performed on those areas. There are times when unit owners may wonder why it appears that work has stopped on a balcony and the contractor has started working on another area. This question usually occurs during the curing/testing period.
“As the dust settles,” Gerwig stresses, “protecting the investment in the repairs is very important. Therefore, the concrete should be waterproofed and painted as soon as possible. The warranty on concrete restoration projects is normally five years on the concrete repairs and waterproofing. Alteration of the repairs, however, may void a warranty. If a unit owner installs tile or carpeting or penetrates the surface of the concrete to install items on a balcony, the warranty will likely be voided.”
“The balcony is typically a limited common element,” notes Pyznar, “so the association is responsible for the structure, but the unit owner is responsible for coverings and keeping it clean. The unit owner could damage the structure, which the association is responsible for repairing, so there should be standard protocol for what can be on a balcony.”
Gerwig points out, “There should be several pages included with each payment requisition that give details of where the work was done, including a drawing of the area. Many times an association will complain several years later that additional concrete is damaged. Unless that specific area was repaired in the previous project, the new damage will not be covered by warranty.”
Concrete restoration parallels dental work in an unfortunate number of ways, one being that delay equals decay, which will increase the scope of the project. “As you wait, costs increase exponentially,” remarks Pyznar. “The staging and access are an expensive part, so you don’t want to be doing it year after year. It’s more cost-effective and less disruptive to unit owners to address all of it at once. If you see signs of spalling or cracks, you don’t want to wait until repair is required for a 40-year inspection. You want to be proactive: it’s the best money you can spend on these structures.”