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Patching: Care And Maintenance – Technical Bulletin #38

The best insurance against chipped stone is care in handling and protection of the unit after installation. Even with all of the special care and protection, building stone still becomes chipped from time to time and a certain amount of patching is to be expected.

Any chip obvious from a 20′ distance should be patched. Chips measuring 1/4″ and less across the face should not be patched and are usually left alone. Stone units with chips larger than 8″ square should be replaced, unless the damaged portion can be salvaged and expoxied back to the unit. Most cracks can be patched if the units are reinforced.

Climatic conditions must be taken into consideration before patching is to commence. Do not patch stone in freezing weather or if a freeze is anticipated within 24 hours. On hot sunny days patching should be done during the morning hours where the Cast Stone is shaded or at temperatures less than 90 degrees Fahrenheit. Patches should be covered with a damp cloth and plastic sheet to prevent the cement from hydrating too quickly.

The same material that was used to manufacture the Cast Stone should be used for patching. Experimental batches should not be used in an effort to obtain an instant color match. The water/cement ration used should be as close as possible to the mix at the time of manufacture. Acrylic acrylic bonding agents may be used, but not in place of water. Use as a wetting agent; less than a tablespoon per handful of patching material.  Never use metal tools for applying a patch. Stones which were acid etched at the factory will require the same treatment applied to the patch.

A properly executed patch will not match in color immediately. Dry cast products will appear lighter where repaired; wet cast products may appear darker. Patches that match immediately or in two or three days have a tendency to change color later on after weathering. Through curing, weathering and ultraviolet light, the patch will eventually return to the original stone color. This process could take 3 months to a year or longer depending on the climatic conditions and exposure to the weather.

Patches which cannot be seen from a 20′ distance when viewed in good typical lighting should be accepted. Request bulletin #36 on Inspection and Acceptance.

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This Technical Bulletin is provided by the Cast Stone Institute, and is intended for guidance only. Specific details should be obtained from the manufacturer or supplier of the Cast Stone units.