Masonry Magazine May 2012 Page. 25
HEAT!
Before repair before cleaning was done to the marble along the joints during the mortar removal process. Although a mortar joint may have been cracked or open on one side, it still was often fully adhered on the opposite side, making the mortar removal a delicate task in the narrow joints found throughout the walls of this marble structure.
A pointing mortar was formulated to closely match the color of the white marble, being sure to also make it softer than the stone substrate. This was created without the use of Portland cement with a product called St. Astier Natural Hydraulic Lime (NHL), which acted as the cement. Although chemically its composition is like hydrated lime, hydraulic lime also includes silicates and other minerals, which help provide an initial set with water much like cement, and a second set by the absorption of CO2, like a pure lime mortar.
There are three versions of NHL mortars, varying in both hardness and setting time. The softest and slowest to set is the 2.0, followed by the 3.5, with the fastest and hardest setting being the 5.0. The repair and pointing mortar was formulated with one part 3.5 NHL to 2.5 parts fine white crushed marble.
Biological staining is the largest cause of discoloration and soiling in most rural settings and in cemeteries, in general. In order for the biological activity to be killed off completely for any length of time, it must be eliminated down to its roots.
D2 biological stone cleaner was applied to the stone when dry, to permeate deeply into the pores of the stone. Light hand scrubbing was performed on all highly stained areas to detach biological growth. A second application of D2 stone cleaner was performed on all severely stained areas. The entire structure was then low-pressure rinsed with clean water.
The D2 will have a delayed affect and, over the course of a few weeks, the biological activity will die off, and the stone will become much cleaner. Marble is composed, primarily, of calcium carbonate, which does not benefit from most types of chemical treatments. Most coatings can and will trap moisture, which can do more harm than good on nearly all historic exterior masonry.
Conservare Hydroxylating Conversion Treatment (HCT) is made by Prosoco. It was applied to the entire structure in multiple coats, followed by the associated finishing rinse. It is a two-component, waterborne treatment that protects and strengthens deteriorating carbonate building stones such as marble and limestone, by forming a stable, well-adhered, conversion layer on carbonate mineral grains.
The entire structure was then also treated with Cathedral Stone Products' breathable Water Repellent, R-97, which does not block the pores of the stone, permitting essential vapor transmission. Additionally, the bronze on the front door and read window frame and grating that had caused long-term staining through copper leaching was cleaned with a product called Chromglanz. The bronze was then masked off, and multiple applications of the solvent-based Incralac were applied. IMAS
Jonathan Appell is owner of Gravestone & Monument Preservation, www.gravestonepreservation.info.
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• Slabs • Sinks • Veneer
Vermont Marble, Granite, Slate and Soapstone Co.
Ph: 866-SOAPSTONE
Fax: 802-419-8233
www.Soapstone Bricks.com
READER SERVICE #180
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45 South Main Street Barre Vermont 05641
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READER SERVICE #167
May 2012
MASONRY
23