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Group Epoxy Repairs in Unreinforced Concrete or MasonryEpoxy is recognized by many experts as a competent repair for steel reinforced concrete. Hoever, for unreinforced concrete or masonry, epoxy has limitations. These limitations need to be understood. Epoxy is a generic term for a family of chemical products, not a single product. Not all epoxies are suitable for construction. To recommend patching a crack with epoxy is much like recommending a wall be repaired with "cementitious material". One may have in mind a 3000 psi concrete when one specifies "cementitious material" and, in fact receive a lean grout or a 2-sack soil slurry mix. One must specify what type of epoxy is required to ensure satisfactory results. For a manufacturer's warranty to be valid, epoxy must be applied to surfaces prepared according to strict published manufacturer's instructions. In addition, manufacturer's warranty requirements require testing of finished work. Installation instructions for epoxies require a clean and dry bonding surface. Application of epoxy to dusty surfaces only ensures a strong bond will occur between the epoxy and the dust. If the crack is not thoroughly cleaned before applying epoxy, cracks can occur under normal stresses such as temperature shrinkage. Many epoxy failures may be attributed to failure to provide the surface environment for epoxy bonding. Cleaning and preparing the surface to receive the epoxy may cost more than materials and applications! Concrete perimeter walls, for example, must be exposed on all sides to allow thorough cleaning of the surfaces to receive epoxy. If only part of the footing is exposed, "cleaning" with compressed air will only blow the dust deeper into an exposed crack. In addition, the City of Los Angeles now requires waivers and special inspections for epoxy installation. Contractors will need to budget for these special inspection fees. Epoxy can be brittle. Although epoxies are quite strong when tested in a tensile strength testing device with a gradual load increase, sharp impacts can cause failure at the point of bonding in construction grade epoxies. Therefore, there is cause to believe cracks may recur in epoxy filled cracks under impact loading from future earthquakes. Such cracks have been observed in slabs which were repaired using epoxy after the Sylmar quake in 1971. Epoxy only repairs the crack into which it is applied. Not all crack damage is confined to a single visible crack. Invisible microcracks may branch from a crack repaired by epoxy or may parallel an epoxy repaired crack. The stress that caused the visible crack may pulverize concrete on the compression side of the crack for several inches on each side of the crack. For this reason, epoxy repairs to concrete may accomplish little other than filling one crack so that a new crack becomes visible at a weakened concrete or masonry plane located 1/4 inch away from the repaired crack. Epoxy will not eliminate beam stresses where soil has been compacted beneath the crack. If the soil beneath a section of the foundation has settled, the foundation may not bear directly on the soil, but may act as a beam spanning soft soil pockets. If new beam stresses have been introduced by the earthquake, new cracks may occur in an unreinforced footing wall near epoxy repairs. The unreinforced concrete was not designed to resist bending stresses introduced by ground movement. Epoxy is inappropriate for exposed finishes. Epoxy repairs have a slick glassy appearance which is not appropriate for exposed slabs or for masonry walls or fireplaces. For surfaces not covered by carpeting, linoleum or tile, the glassy appearance of the epoxy decreases the architectural quality of the exposure and devalues the property. Back to the Home page. [ Real Property ]
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