Brownstone Restoration

Composite repair, the application of a tinted mortar-like patch to the surface of a deteriorated stone or portion of a stone, is one of the most common techniques utilized to repair deteriorated brownstone surfaces. Composite repairs are appropriate where small areas of mechanical damage have occurred or where the entire face of a unit has exfoliated. Composite repairs last longer in locations that do not have heavy exposure to rain. Composites applied to windowsills and wall copings often fail prematurely, due to water infiltration and disaggregation of the stone beneath the repair. In areas where direct wetting of the patch is not a problem, such as sheltered vertical wall surfaces, composites may be very durable. Satisfactory adhesion of a composite repair requires removal of all deteriorated stone down to solid material. The sound stone is then scarified or roughened to provide some mechanical anchorage for the composite patch. For large repairs, rods and wire armatures are sometimes added to provide additional support and to assure that the patch does not separate from the substrate. The rods can be made of fiberglass, nylon, or stainless steel. A durable composite repair must be at least 3/4” thick.

Due to the difficulty of exact color matching, composites applied to the full face of a deteriorated stone unit are the most successful visually. Usually, it is preferable to apply composite repairs separately to individual stone units, stopping the edge of the repair at the mortar joint that separates the unit from adjacent stones.