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Products like cast stone and rockfaced concrete blocks have existed in the United States since the early twentieth century. Simulated masonry is similar to both because it too imitates other material. The construction of simulated masonry is made to be more flexible than rockfaced concrete blocks or cast stone. Simulated masonry was traditional cast on site and applied as a facing material. This process allowed for maximum adaptability for specific and unexpected site conditions. Simulated masonry was traditionally marketed for new construction but was later seen as a viable way for updating older homes. The process of updating or creating a home with simulated masonry proved less costly than the application of actual stones but could convey the same sense of permanence. The changing aesthetics of public buildings in the 1930s was due in large part to simulated masonry. One of the more prevalent types of simulated masonry was Perma-Stone, which claimed to be one of the first molded stone wall-facings. The Perma-Stone company emerged in 1929 out of Columbus, Ohio and sold its trademarked product only through licensed and fully trained dealers. The mixture of Portland cement, aggregate, mineral colors, crushed quartz and metallic hardeners was provided to the dealers, along with the necessary molds. The dealer was then responsible for mixing, molding, and installing the material. Soon, many similar companies surfaced to try to capture of piece of the developing market. Another popular simulated masonry company was the Lasting Products Company, which produced Formstone. Formstone was first available in 1937, immediately following the acquisition of a patent by Lasting Products. Like Perma-Stone, Lasting Products would send the tools and materials to a registered contractor that had been trained by the company. The contractor was then responsible for mixing and installing the product. Simulated masonry was thought to be a highly modern invention. Rostone (pressurized shale, alkaline earth, lime, and water) was first introduced at the Century of Progress Exposition. Rostone was a product of the Rostone Company in Indiana and was first used to create the Wieboldt-Rostone House. This house was one of ten houses used to exhibit the modern material and innovative construction methods. Rostone was prefabricated panels that were shipped to the construction site to be installed by a trained contractor. Other materials could be used besides cement. Fiber reinforced plastic panels saw a rise in popularity in the 1960s. A product named Terox could be molded in a cast that emulated select quarry stones. Other products used pigment to match the desired stone color.
 Manufacturing Process
Simulated masonry can be broken down into two distinct categories: those mixed off site and those mixed on site. Regardless of where the material is mixed, both can be applied to an existing structure or as part of new construction for most building types. Rostone was created to emulate not only the appearance but also the formation of natural stone. Rostone did not use cement, it was commonly made of natural ingredients that underwent a chemical reaction to form new materials. To begin, shale was dried, pounded, and finely ground. The next step included adding lime and water and then placing the material into hand-formed molds into a specific shape. The mixture was then hardened through heat. The material could be colored during manufacturing and a finish could be applied afterward. After cooling, Rostone was ready to be shipped to the construction site.
 Uses and Installation
Though this material was usually used for remodeling, application for new construction was also possible. Simulated masonry was popular for several reasons. Simulated masonry was perceived as a sign of wealth and grandeur and as a modern version of natural stone. Middle-class Americans enjoyed the prestige of a “stone” house without the expense of natural stone. Manufacturers sold their product on the basis that every-day Americans could afford a home that resembled the upper echelon of society. Also, the stone was marketed as being maintenance free and fireproof. Buyers found simulated masonry to be an inexpensive way to modernize a building or covering a deteriorating façade. Perma-Stone was often marketed as a new construction material but was used extensively in remodeling. Formstone was used more often for new construction.
Rostone was meant to be an easy way to modernize store fronts. The Rostone Company also marketed their product towards residential areas, claiming their material was useful in constructing interior walls, floors, and decorative elements (commonly around fireplaces). The panels came in standard sized sheets of 16-by-24 inches that were between 1 and 1 ¼ inches thick though custom sizes could be purchased for an additional fee. The surface of these sheets could come in three different textures: honed (polished), natural (slightly rough finish that mimicked natural stone), and shot blast (a moderately rough surface). While earth tones colors were the most popular, a variety of colors were offered. Greens and reds were popular accent colors in carved designs and usually conveyed a multidimensional look. In remodeling projects, Rostone panels were usually applied over an existing surface. In new construction, the panels were attached to steel frames with special clips and the joints filled with mastic.
Perma-Stone was a cementitious material that is produced on site and applied to the building directly like stucco. Perma-Stone was popular in remodels because of a stone-like concrete veneer that can permanently attach to wood or steel or can be applied directly onto concrete or masonry. Perma-Stone is installed using a metal or wood lath that is secured to the building as a base attachment. The application is done in three steps. A brown coat, or first coat, is applied over the board (lath) and allowed to dry. A second coat (scratch coat) is applied next, followed immediately by a finish coat. The finish coat is applied while the scratch coat is still wet and is applied with the use of pressure molds made to look like natural stone. Hand finishing is minor and the application of a final film coating is applied to repel water. Perma-Stone can be applied to curved or flat broad surfaces. It can be random, broken, or coursed ashlar. The joints can be raked, beaded, or pointed and color choice is unlimited. The variety of color allows for the development of interesting strata and varied stone color. The texture of the material is limited only by the mold or the hand finishing. Perma-Stone is the most popular simulated masonry and the Perma-Stone Company passionately protected its trademarks and was more than willing to go to court against those who used it without permission. It has several patents covering its recipe for production, pressure-casting procedure, and membrane-curing techniques. Only licensed dealers are permitted to use the process, molds, and materials.
Formstone was developed with the idea of finding a process to make artificial stone facing that would use the tools of masons and cement finishers. Formstone and Perma-Stone share several similarities in that they are both a cementitious material that is applied in multiple layers. If Formstone is applied to a masonry or stone wall, then the use of a lath is no longer necessary. Cement mortar is applied over the lath, with this layer traditionally being scored before it dries. A second layer is applied after the first has dried. The finish layer is applied while the second layer is still plastic. The finished layer can be formed with multiple shades or colors of mortar cement that are distributed to produce the polychromatic effect desired for the appearance of the stone. While the top two layers are still moist, waxed paper is placed on the wall. A cast aluminum roller with a crinkled surface passes over the paper, making a crinkled appearance in the mixture. Different sizes or textures can be used on the same project to achieve nearly any desired effect. The waxed paper is immediately removed (after the desired effect has been achieved) and the surface is then scored with guide lines for mock mortar joints. Grooves are cut into the top layer with a chasing tool to create mortar joints mimicking that of a natural stone structure. The mortar joint can be left unfinished or pointed with mortar. Different finishes, textures, and colors can be created. Most tinting is created by adding color in the mortar mix, though dashing colored powdered dust can be added to an already formed surface. This product will speckle the surface and is meant to simulate natural rocks or stones. The powdered material should be applied before the wax paper is applied or after it has been removed. Formstone was promoted as a material that could address masonry or stone problems or poor insulation. Formstone came with a twenty year guarantee that the wall facing would be maintenance free. Simulated masonry reached the pinnacle of its popularity in the 1950s and interest in the products of this nature was nearly nonexistent by the 1980s. Vinyl and aluminum siding were being mass-produced and were more economically installed. These products also addressed the change is aesthetic appeal. Perma-Stone and Formstone are still produced in small quantities today.
- Milkovich McKee, Ann. "Simulated Masonry." Twentieth-century Building Materials: History and Conservation. By Thomas C. Jester. New York: McGraw-Hill, 1995. 174-79. Print.
- Ann Milkovich McKee, "Stonewalling America-Simulated Stone Products," CRM Magazine, vol. 18 no. 08 (1995. Available online at http://crm.cr.nps.gov/archive/18-8/18-8-6.pdf
- Paul K. Williams, "The Faux Stone Follies: Deciding whether to remove Perma-Stone and other simulated masonry can leave homeowners between fake rock and a hard place," Old House Journal (June 2003). Available online at http://www.oldhousejournal.com/magazine/2003/june/faux_stone.shtml
- Paul K. Williams, "The Story Behind Formstone," available online at http://welcometobaltimorehon.com/the-story-behind-formstone