How Do I Know What Shape My Balcony Is In?
Towers Topics Newsletter Reprint, June 2016
By George Gardner, General Manager
All balcony owners are wondering about the process used to determine whether their balconies need repair.
Evaluation of the condition of the concrete floors starts with an inspection by a qualified structural engineer with a visual examination for cracks, spalls (splinters or chips of concrete), or other signs of distress. Then the concrete is sounded to help determine the extent of deterioration that requires repair.
Sounding involves various activities, such as (1) dragging chains across the top horizontal surface, and (2) using hammers, steel rods, etc. to strike (tap) the concrete surfaces. When concrete is sounded, a clear “ringing” audible sound is generated. A distinctly different sound pitch results when testing competent concrete as opposed to deficient concrete. When deteriorated concrete is sounded, a dull, hollow, audible sound is often produced which indicates concrete delamination (separation) below the surface being tested. This allows the person performing the inspections to determine the approximate location and extent of concrete deterioration that requires repair.
The process of sounding concrete to check for deterioration has been in existence for many years and is considered an industry standard practice. There is a specific accepted standard called ASTM standard D4580 that outlines the practice of sounding to help determine general conditions.
It is important to note that the industry standard practice of “sounding” is an approximate estimate of deteriorated concrete. The full extent of deterioration is often not revealed until actual repairs have been initiated and hence can influence the final extent of work needed to restore the slab. This in turn means that there can be variation, sometimes significant variation, in the initial cost estimate used to project the possible cost of repairs. This makes the task much more difficult in terms of giving owners precise estimates of cost.
Experiments have been conducted using other techniques to evaluate concrete, including but not limited to, ground penetrating radar (GPR), ultrasound, and radiography (x-ray). These techniques are much more expensive than the industry standard of sounding concrete with chains, hammers, etc. Except for use on thick concrete (not the thin balcony slabs at the Towers) these techniques have not proven to provide more significantly reliable information that the standard “sounding” technique.
All of these techniques, including the industry standard practice of sounding, are considered unreliable when a concrete balcony slab has a covering of tile, carpet, etc. The boundary layer between the structural concrete and the covering distorts and negates the feedback and data received from the testing.
Hence, the only alternative for covered balconies is to first remove the covering to arrive at an indication of concrete deterioration. The costs associated with removing coverings on top of balcony slabs can vary widely based on a number of factors, particularly the type of material, the material thickness, and how well the material is bonded to the balcony slab.
In 2014, we completed field investigation of approximately 300 of the 408 balconies to determine condition at that time. About 80 balconies were not inspected due to the presence of coverings on the balcony while an addition 39 balconies were not surveyed as they had been repaired in 2013-2014. Further deterioration since the 2014 inspection has undoubtedly occurred. The additional deterioration can vary widely from balcony to balcony and cannot be more precisely estimated without an additional field survey.
One other point to be aware of: after a balcony slab is properly repaired and coated with a protective covering, inspections should be performed on a five year cycle. Balcony deck coatings are typically guaranteed by the manufacturer for five years, so this is a good time to inspect coatings and other balcony components.