Masonry buildings historically last hundreds of years. Eventually they will need repair and restoration. It is critical that this be done absolutely correct. Proper structure and material analysis are the first steps to a successful restoration project. You can find examples of our projects in our portfolio area.
Historic Masonry Restoration Duluth, MN.
Johnston Masonry is the most qualified and experienced masonry company in the Northland with restoring and maintaining historic masonry buildings and features. We take great pride in the successful projects completed to this day and continue to provide undeniable service and results. There are many such buildings and features in Duluth and the surrounding areas that, with our expertise, can continue to remain, and look as they did when first built, for a lifetime.
Terra-Cotta repairs in progress in Downtown Duluth, MN. Read more in the Duluth News Tribune article.
Masonry—brick, stone, terra-cotta, and concrete block—is found on nearly every historic building. Structures with all-masonry exteriors come to mind immediately, but most other buildings at least have masonry foundations or chimneys. Although generally considered “permanent,” masonry is subject to deterioration, especially at the mortar joints. Re-pointing, also known simply as “pointing”or—somewhat inaccurately—”tuck pointing”*, is the process of removing deteriorated mortar from the joints of a masonry wall and replacing it with new mortar. Properly done, re-pointing restores the visual and physical integrity of the masonry. Improperly done, re-pointing not only detracts from the appearance of the building, but may also cause physical damage to the masonry units themselves.
Portland cement was patented in Great Britain in 1824. It was named after the stone from Portland in Dorset which it resembled when hard. This is a fast-curing, hydraulic cement which hardens under water. Portland cement was first manufactured in the United States in 1872, although it was imported before this date. But it was not in common use throughout the country until the early 20th century. Up until the turn of the century portland cement was considered primarily an additive, or “minor ingredient” to help accelerate mortar set time. By the 1930s, however, most masons used a mix of equal parts portland cement and lime putty. Thus, the mortar found in masonry structures built between 1873 and 1930 can range from pure lime and sand mixes to a wide variety of lime, portland cement, and sand combinations.
Image by Dean Johnston
Preliminary research is necessary to ensure that the proposed re-pointing work is both physically and visually appropriate to the building. Analysis of un-weathered portions of the historic mortar to which the new mortar will be matched can suggest appropriate mixes for the re-pointing mortar so that it will not damage the building because it is excessively strong or vapor impermeable.
Examination and analysis of the masonry units—brick, stone or terra-cotta—and the techniques used in the original construction will assist in maintaining the building’s historic appearance. A simple, non- technical, evaluation of the masonry units and mortar can provide information concerning the relative strength and permeability of each—critical factors in selecting the re-pointing mortar—while a visual analysis of the historic mortar can provide the information necessary for developing the new mortar mix and application techniques.
Although not crucial to a successful re-pointing project, for projects involving properties of special historic significance, a mortar analysis by a qualified laboratory can be useful by providing information on the original ingredients. Johnston Masonry sends mortar samples to Edison Coatings for an exact mortar match.
Johnston Masonry follows the U.S. Technical Preservation Services for all restoration projects.
(Information has been gathered from U.S. Preservation Briefs)
Generically, the broadest definition of terra-cotta refers to a high grade of weathered or aged clay which, when mixed with sand or with pulverized fired clay, can be molded and fired at high temperatures to a hardness and compactness not obtainable with brick. Simply put, terra-cotta is an enriched molded clay brick or block. The word terra-cotta is derived from the Latin word terra-cotta—literally, “cooked earth.” Terra-cotta clays vary widely in color according to geography and types, ranging from red and brown to white.
Historically there are four types or categories of terra-cotta which have enjoyed wide use in the history of the American building arts: 1) brownstone, 2) fireproof construction, 3) ceramic veneer, and 4) glazed architectural.
Crazing, or the formation of small random cracks in the glaze, is a common form of water-related deterioration in glazed architectural terra-cotta. When the new terra-cotta unit first comes from the kiln after firing, it has shrunken (dried) to its smallest possible size. With the passage of time, however, it expands as it absorbs moisture from the air, a process which may continue for many years. The glaze then goes into tension because it has a lesser capacity for expansion than the porous tile body; it no longer “fits” the expanding unit onto which it was originally fired. If the strength of the glaze is exceeded, it will crack (craze). Crazing is a process not unlike the random hairline cracking on the surface of an old oil painting. Both may occur as a normal process in the aging of the material. Unless the cracks visibly extend into the porous tile body beneath the glaze, crazing should not be regarded as highly serious material failure. It does, however, tend to increase the water absorption capability of the glazed architectural terra-cotta unit.
Spalling, the partial loss of the masonry material itself, is, like crazing, caused by water and is usually a result not only of airborne water but more commonly of water trapped within the masonry system itself. Trapped water is often caused by poor water detailing in the original design, insufficient maintenance, rising damp or a leaking roof. In most cases, trapped water tends to migrate outward through masonry walls where it eventually evaporates. In glazed architectural terra-cotta, the water is impeded in its journey by the relatively impervious glaze on the surface of the unit which acts as a water barrier. The water is stopped at the glaze until it builds up sufficient pressure (particularly in the presence of widely fluctuating temperatures) to pop off sections of the glaze (glaze spalling) or to cause the wholesale destruction of portions of the glazed architectural terra-cotta unit itself (material spalling).
(Information has been gathered from U.S. Preservation Briefs)
These are the steps in order for restoring Terra-Cotta. The first step is a thorough inspection consisting of recording visible damage and taking samples for research. The samples are sent in for analysis by Edison Coatings who gives us a exact color match and materials for restoring the damage. The images are analyzed for deterioration and reason for damage and prevention methods are decided. Once a plan of action has been formed the restoration work is commenced.
Terra-Cotta Cap Restoration by Johnston Masonry