The Cleaning Restoration of the exterior masonry cladding of The Landmark Office Towers and Terminal Tower complex downtown Cleveland was required since both buildings were covered with massive calcium sulfate scabs. The problem was that the materials soiling the surfaces of the limestone exterior were calcium sulfate encapsulated pollutants.  These pollutants are encapsulated in crystals which are white but use suspended particulate from industry and auto emissions as a crystallization nuclei and as a result form a black pollution sink against the masonry surface.  This formation can cause vapor transmission to be hampered plus dramatically increasing the likelihood that salts forming in the substrate (sub-florescence) which can lead to spalling or exfoliation of the surface.

Hart Restoration was called in to clean and restore the exterior limestone of the massive complex of buildings using its ARM system (Advanced Restoration of Masonry).

Hart’s Treatment took in consideration that calcium sulfate crusts are very hard and pressure washing alone is not an effective treatment for removal of these crusts.  The pressures that would be required would also damage the masonry surface.  Acid based cleaning products are also inappropriate as acids will react with the limestone surface causing dissolution of the limestone and leaving the surface etched.

The calcium sulfate crusts are slightly water soluble in cold water which accounts for the fact that the crusts are heaviest in the areas that are somewhat protected by rainfall such as under window ledges and the cornice of the building.  The best treatment for removing these crusts is to take advantage of the natural solubility of the calcium sulfate without over-saturating the masonry.

Hart Restoration Group has perfected a system for dissolving calcium sulfate crusts using pulses of a cold water mist.  The pulses are interspersed with dry cycles to control the depth of water penetration into the masonry substrate.  This system cleans the calcium sulfate based contaminants from the stone leaving a new a clean appearance to the building.