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<br />Recommended <br /> <br />Rehabilitation <br /> <br />Not Recommended <br /> <br />Building: Exterior Features <br /> <br />Masonry: Adobe, brick, stone, terra cotta, concrete, stucco, and mortar <br /> <br />Retaining original masonry and mortar, whenever <br />possible. without the application of any surface treat- <br />ment. <br /> <br />Repointing only those mortar joints where there is <br />evidence of moisture problems or when sufficient <br />mortar is missing to allow water to stand in the mortar <br />joint. <br /> <br />Duplicating old mortar in composition. color, and <br />texture. <br /> <br />Duplicating old mortar in joint size. method of appli- <br />cation, and joint profile. <br /> <br />Repairing stucco with a stucco mixture that duplicates <br />the original as closely as possible in appearance and <br />texture. <br /> <br />Cleaning masonry only when necessary to halt deteri- <br />oration or to remove graffiti and stains and always <br />with the gentlest method possible. such as low pres- <br />sure water and soft natural bristle brushes. * <br /> <br />Applying waterproof or water repellent coatings or <br />surface consolidation treatments unless required to <br />solve a specific technical problem that has been <br />studied and identified. Coatings are frequently unnec- <br />essary, expensive. and can accelerate deterioration of <br />the masonry. <br /> <br />Repointing mortar joints that do not need repointing. <br />Using electric saws and hammers to remove mortar <br />can seriously damage the adjacent brick. <br /> <br />Repointing with mortar of high Portland cement <br />content, thus creating a bond that can often be <br />stronger than the building material. This can cause <br />deterioration as a result of the differing coefficient of <br />expansion and the differing porosity of the material <br />and the mortar. <br /> <br />Repointing with mortar joints of a differing size or joint <br />profile, texture, or color. <br /> <br />Sandblasting, including dry and wet grit and other <br />abrasives. brick. or stone surfaces; this method of <br />cleaning erodes the surface of the material and <br />accelerates deterioration. Do not use chemical cleaning <br />products that would have an adverse chemical reac- <br />tion with the masonry materials. i. e.. acid on limestone <br />or marble. <br /> <br />'" For more information consult Preservation Briefs: 1. "The Cleaning and Waterproof Coating of Masonry Buildings" and Preservation Briefs <br />2, "Repainting Mortar Joints in Historic Brick Buildings," Both are available from Technical Preservation Services Division, Heritage <br />Conservation and Recreation Service. Washington. D.C. 20243. <br /> <br />27 <br />