The following is an excerpt from a report prepared by BFI on an Airport Parking Structure:
"BFI has been retained to make a brief visit to the above
captioned project, evaluate the nature, distribution and extent
of efflorescent materials present thereon, provide limited
testing services, and prepare this report. The specific
assignment of the investigation was to examine and consider
the manifestation of efflorescent materials present on the
structure, particularly at painted locations, recommend and
perform tests, and prepare this and a supplemental report. The
structure is a four story post-tensioned concrete structure with
multiple architectural features and accents, including the paint
on exterior formed concrete surfaces which are exposed to the
weather. The parking decks feature a built up section adjacent
to most of the perimeter vertical walls, accentuating surface
drainage positively away from them. Despite this, there were
selected locations where this detail was less effective and the potential for ponding was noted, especially around the stairwells. Efflorescence on concrete was detected at some of these locations.
It is reported that painted portions of the structure have been cleaned a number of times and they have experienced a number of paint touch up treatments. Cleaning has been required primarily due to the accumulation of efflorescent materials on painted surfaces.
Observations on the unpainted concrete surfaces from all
around the structure reveal that efflorescence is neither prevalent nor problematic in these areas. Predictable, minor, and acceptable amounts of efflorescence are present on unpainted concrete surfaces which are some exposed to moisture and evaporative moisture loss. At locations, efflorescence appears on the back sides of walls which face exposure to rain and/or ponded water. However, at painted areas which are generally exposed to moisture, the frequency of patchy, white efflorescence deposits and their extent and size is excessive and unusual. In some cases, the patches of efflorescence appear in repeating patterns and spacing, with similar distances between patches. One observation of interest is that not all painted surfaces exhibit efflorescence. It appears that the areas of efflorescence on the painted areas originate from beneath the paint and travel due to moisture gradients across the paint, travel down and outward from the painted surface, later to dry on exterior faces due to sunlight and heat, leaving behind tracks of once dissolved salts now dried.
As the observations progressed it became apparent that the color and texture of the sacking materials varied from location to location and from sacked blemish to sacked blemish. Based upon their color and texture, it appears that at least three different materials were used for sacking activities.
Hundreds of form tie patches were observed in the project. Some were made with very dark grey, hard material with a rough sandy finish, some were made with grey to light grey materials with various textures and grits, some were made with very white material of extremely smooth finish texture. While the light and dark grey materials appear to be portland cement based, the white materials appeared to be similar in color and texture to gypsum based products. Portland cement and sand formulations contain materials appropriate for such patches; gypsum based materials are inappropriate for patching concrete work such as this. Gypsum based materials are susceptible to alteration and progressive dissolution by water. Gypsum based materials can dissolve over time, primarily yielding calcium and sulfate deposits, but possibly including soluble alkalies and other alkaline earth metals (usually sodium and potassium, and possibly magnesium) as well.
Efflorescence is caused by the progressive leaching, dissolution, transport of soluble mineral compounds by liquid water and their subsequent precipitation and deposition on surfaces by drying. It is necessarily a demonstration of the action of water and heat on materials so exposed. While there is a slight amount of such soluble materials in concrete and cement based patching materials, the amount, pattern and distribution of efflorescence on the majority of unpainted surfaces and non-white patching materials is trivial. It can be concluded with confidence that the source of the efflorescence is largely unrelated to the concrete mass itself. Further, the efflorescence appears to be unrelated to the dark and/or light grey sacking materials. The white sacking material appears to be the source of the soluble efflorescing salts. Testing in progress may confirm this theory. The demonstration of calcium sulfate in the white material will constitute strong evidence in this regard. Alternatively, demonstration of soluble alkalies and/or other alkaline earth metals can lead to useful clues regarding the offending materials.
In summary, the subject structure has experienced multiple events of patching and sacking with a variety of materials, each with its own performance characteristics. Of the materials used, it appears that one or some are more sensitive to moisture than others, and display a greater tendency to dissolve and mobilize by means of moisture from dew, condensation, rain, cleaning activities, or other unidentified sources, and precipitate as efflorescence elsewhere due to thermal and drying effects. While the efflorescence is less frequent and objectionable on concrete surfaces, it is particularly visible and unacceptable on painted surfaces where the color and texture contrast is greatest.
While this report tentatively identifies the white patching material and hypothesizes that it is gypsum based or high in soluble alkalies/alkaline earth metals, or both, additional work is required to confirm this opinion with confidence."