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The following is a recommendation for Patching, Care and Maintenance of Cast Stone Material.


Careful quality assurance and control of the cast stone on-site are important as chipping and cracking will occur if the cast stone is not properly handled. Ongoing inspection at the job site will keep all parties informed of the expectations and progress of the project.


Even with careful control and handling, chipping may occur and patching can be expected. A good rule of thumb to follow is that any chip that is visible from a twenty-foot distance should be patched. Any chip that is one-quarter inch or less on the face of the cast stone should be left alone. Any piece that has a chip of eight inches or greater should be replaced, unless you feel that it can be patched, or epoxied back into place without compromise. If the cast stone pieces are properly reinforced, most cracking can be patched with proper care.


Weather plays an important factor on when to install and patch. Do not patch on either freezing or extremely hot days. Do not patch when freezing weather is expected within twenty-four hours, or in hot sunny areas over 90°F. The best rule of thumb to do any patching is in weather that is at least 46°F, 60°F being best. For days that will hit 90°F or higher, we strongly suggest that you patch in the early morning and in a shaded area. Additionally, covering the patch with a damp cloth and a plastic sheet will prevent the cement from drying too quickly.


Patch kits should be made from the same mix that the original pieces were made with. Water,  cement, and sand rationing should be close to that of the original mixture. Generally, the mix is three parts sand to one part cement, plus any pigments that the recipe called for.

Add water to make the mix pliable but not too moist. The desire is for zero slump. This is not a wet pour cast product.


Use a spray bottle with water to drench the area requiring patching. An acrylic bonding agent can be used with the patch kit. Less than a tablespoon of the acrylic bonding agent can be used per each handful of patch kit material. Do not replace the water with the bonding agent; water is necessary for proper consistency of the patch kit mixture. Test the patch kit with the bonding agent prior to patching to ensure that the patch does not appear whiter than the original cast stone after drying. If it does, moisten the area to patch, then place a small amount of agent on the chipped portion of the cast stone piece, keeping it away from the edges of the crack. Apply the patch kit material (without bonding agent) to the crack and finish off the edge. The finished piece should conform to the design of the piece mark.


It is best that you do not use metal tools when applying the patch kit material to the cast stone; use wooden or plastic tools. Do not use too many strokes as it will produce a slick, sometimes, glossy, surface. If you leave a little bit extra material on the patch and let it sit for a short while, you can brush it with a soft brush, a piece of carpet, a sponge, a piece of sandpaper, a coarse rag, or something that can give it a rougher finish like the mortar blending.

The acrylic bonding agent can be found in most large home improvement stores.


If the cast stone has been acid washed at the manufacturing plant or later on-site, this same treatment needs to be applied to the stone with the patch. It is a good rule of thumb to wash the entire project with the same solution, at the same time, to ensure consistency of color and texture.


Even with the utmost care and proper patching, please note that color will not match immediately. Dry cast stone products appear lighter than wet cast stone products. It could take up to six to twelve months for the material color to blend after patching.


Depending on the timing of the patch, it is important to consider the following. All materials have been manufactured with the same sand. Sands change throughout the mining process and color control by quarries is impossible to exactly match on a continuous basis. Should you require a patch kit later down the line, please keep in mind that the color and aggregate consistency of the sand can change, even minimally.


Patching has a tendency of being a different color than the original, at the start. Curing, weathering, and ultraviolet light will eventually turn the stone to the original color. Curing, weathering, and ultraviolet light, as well as, any staining from trees or roofing, will change the color of the cast stone throughout time. Patching with that existing color will be impossible to match but throughout time, natural weathering and curing will tend to match the colors. This process can vary in time and up to a year before the colors match.


If you have used a cleaner on the other stone or plan on doing a full cleaning on the project at once, wait five to seven calendar days for the patching material to cure.


If water repellent were used on the original project, it is strongly recommended that you use water repellent on newly patched stone as well. If you have chosen not to use a water repellent on the entire project, you may want to seriously consider its use. If you have material that is in moist areas, such as planter boxes, and along walls that are constantly watered, you may want to seriously consider using water repellent on at least those surfaces.


Note that careful planning at the start will assist in eliminating disappointment for any homeowner or commercial designer at the completion of the project.


When trying something new, test out the patching on an area that is not visible or on a sample stone so you can get the feel of what is required and the color that the patch kit will produce. Obviously, the drying time can be up to twelve months but one can get a good feel for how the patching will measure up to the cast stone already installed.


There is so little one can do to change the appearance of cast stone after installation; therefore, we strongly suggest that careful consideration and planning are executed from the start.




The information within this and all our bulletins has been provided as a guideline and based upon statistical data and prior uses. We always suggest that you consult with your engineer, architect or contractor for the best design and use of cast stone for your project. Our design team is always available to answer any of your questions. We do not accept any liability from damages resulting from your interpretation of the data contained within.