Touchup and Repair
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 touch up is to be expected. Damage to stone either while in transit or during installation is usually classified as repair.
Touch up - Any chip obvious from a 20’ distance should be touched up with material provided by the manufacturer. Chips measuring 1/4” and less across the face are usually left alone. The stone mason should include touch up as part of the ordinary pointing and washdown operations prior to final inspection.
Repair - Chips measuring larger than 1/4” across the face are usually addressed in a separate operation as soon as possible following occurrence of damage. The procedure for repair will include dressing the damage and applying fresh material to achieve the desired finish and shape, covering the repair with a wet rag and/or plastic cover, then taking steps to blend the repair into the adjacent areas. 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 repaired if the units are reinforced. Units which are load bearing should be epoxy injected after the cause of the restrained movement has been identified. Cracks which are observed in installed units can be grouted with native material if the crack is less than .007 in. and the forces which caused the crack have been eliminated.
Climatic conditions must be taken into consideration before repair is to commence. Do not repair stone in freezing weather or if a freeze is anticipated within 24 hours. On hot sunny days repair should be done during the morning hours where the Cast Stone is shaded or at temperatures less than 90 degrees Fahrenheit. Repairs 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 touch up and repair. Experimental batches should not be used in an effort to obtain an instant color match. The water/cement ratio used should be as close as possible to the mix at the time of manufacture. Acrylic bonding agents may be used, but not in place of water. Use as a wetting agent; less than a tablespoon per handful of the concrete material. Never use metal tools for applying a repair. Stones which were acid etched at the factory will require the same treatment applied to the touch up or repair.
A properly executed repair will not match in color immediately. Dry cast products will appear lighter where repaired; wet cast products may appear darker. Repairs 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.
Repairs which cannot be seen from a 20’ distance when viewed in good typical lighting should be accepted. Request Bulletin #36 on Inspection and Acceptance.
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.