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CARE AND MAINTENANCE—DETERIORATION, AGING, AND REFINISHING

 

The following is a recommendation for handling Deterioration, Aging and Refinishing of Cast Stone Material. Cast stone material is subject to deterioration, chipping, scaling, flaking, separation, and erosion. We will attempt to provide a simple overview of each type of concern with some corrective measures that you might want to explore as well as those that you may not want to attempt.

 

Note that cast stone color and texture are subject to changes throughout the years. Aging through inclement weather, sun bleaching, staining from trees, roofing material, mold, mildew, and algae changes the appearance of the cast stone. Matching the color of the repaired work to the current color is almost impossible. Sands change continuously thus matching the exact sand color and aggregate, will not be an easy task.

 

Manufacturers, masons, and contractors can come close to the same color but time, aging and weathering will have to transpire before the repair is unnoticeable. Time and patience are necessary in any repair. Proper precautions during manufacturing, installation, and maintenance will help minimize the chances of some of these occurrences.

 

Anchors, Ties, Cramps and Reinforcement Deterioration

 

Anchors are devices, metal, ties, bolts, inserts, or fittings that are used to attach masonry units, including cast stone, to other masonry units or structures. Cramps are strips of metal with ends bent at right angles.

 

Steel reinforcements (rebar) are usually added to the cast stone material during the initial manufacturing process when they can be placed at least on a half inch from the face or surface of the finished cast stone. If the material is placed too close to the surface of the cast stone and the surface of the cast stone material is damaged, the reinforcement material can discolor or rust depending on the type of reinforcement material that was originally used.

 

Regardless of whether or not internal reinforcements of cast stone were used, exterior reinforcements (anchors, ties, or cramps) are used to secure the cast stone to other masonry units or the main structure. If the cast stone material has moved over time resulting from inclement weather conditions, moisture, shrinkage, and settling, gaps may appear allowing environmental agents to deteriorate the reinforcements.

 

Chipping, cracking, and any other damage to the cast stone material, as well as joints and sealants, also allow environmental agents to deteriorate the reinforcements. Cast stone units that have predominantly thin joints are subject to deterioration where chips, or spalls, have taken place.

 

Two primary examples of such deterioration are in the upper areas of ashlar or in frieze units. Ashlar units are usually large masonry units that are dressed, or decorative stone units that have square cuts, used as facing stone on walls of stone or brick, usually of greater size than eleven inches, and that have been set with thin joints.

 

Frieze units are horizontal bands of sculptured material or a part of an entablature (a continuous lintel support supported by columns or a wall). The entablature consists of a cornice, frieze, and architrave—the uppermost portion of column structures.

 

Deterioration of the cast stone material

 

Deterioration of cast stone caused by deterioration of the aggregate is uncommon. What one suspects is a deterioration of the cast stone is usually the weathering or aging, mildew, mold, algae, discoloration from trees, saps, roofing materials, and such, that stain the cast stone.

 

Proper water repellents and sealants should be applied at the end of each project to help prevent this type of occurrence. Applications should be repeated every five to ten years depending on the repellent used and the environmental conditions.

 

There is a possibility that a reaction occurs between the alkalis in the cement matrix and the sand or stone aggregates used during manufacturing that can cause deterioration.

 

Flaking of cast stone material

 

Flaking of cast stone products made with today’s technology is very uncommon. There are many possibilities for flaking that one would see typically on older masonry units.

 

The individual components used to manufacture cast stone is important, as well as their proper storage. Cement that has been improperly stored, or is of poor quality can create a problem with the mix. Impurities in water can be a subject of concern. Set accelerators and admixtures can also create problems years later. Improper mixing of the ingredients, improper use of admixtures, and improper tamping (compaction) can result in a cast stone material that is porous, leaving it susceptible to flaking, scaling, or chipping especially in areas of extreme temperatures. Unfortunately, if flaking, chipping, and scaling are an occurrence of the cast stone material, it makes it very difficult to repair. Those pieces that are experiencing this type of deterioration that is unattractive or may allow further deterioration to the integrity of the structure may need to be replaced.

 

Separation

 

As with flaking, scaling and chipping of the cast stone material, separation of the facing and core layers of the cast stone may occur. Manufacturing considerations are suspect when this type of deterioration occurs. Poor cement, impure water, improper use of admixtures, and set accelerators, improper mixing techniques, poor tamping techniques, length of time the mixture has been sitting prior to tamping, or the mixing of batch mixtures (wet and dry mixtures in layers) and improper curing techniques are all possible reasons for separation of cast stone materials.

 

Surface erosion

 

Although not as serious as flaking, scaling, or chipping due to possibly improper manufacturing techniques, surface erosion may be seen. This is usually caused by a deterioration of the cementing mixture of cast stone pieces that have profiles that project and are subject to water runoff or water collection.

 

Such items as sills, coping, or banding that have been improperly installed to act as a gutter, or are improperly sloped, are subject to erosion. Water tables and lower portions of the buildings and planter boxes, fountains, and garden décor that are subject to excessive moisture are more susceptible to erosion than those items that are on the interior, or protected from standing water and moisture and were properly protected with water repellents.

 

Although not the intended surface texture, the erosion makes the cast stone rougher in nature. Depending on the size of the aggregate in the overall mix, the roughness may be more prominent in some cast stone pieces than in others. Unless you replace the pieces, there is not much you can do with this type of erosion.

 

In the past, history has shown that a fine layer of decorative tooling was applied to the outermost portion, or facing of the cast stone pieces. This décor was not originally part of the mold that the cast stone mixture was tamped or compacted in. It was usually made up of a thin layer of cement, sand, and color pigments to give the desired decorative effect of that era. This thin decorative outer layer had a tendency to erode and separate from the originally manufactured cast stone.

 

The running of color pigments in these erosion areas may also cause unwanted staining. The cracked, scaled, flaked, separated, or chipped outer layer is difficult to match. It is not recommended that one patch this type of deterioration. Since it has been seen throughout history that placing a fine layer of material on the face of a cast stone piece will deteriorate over time, it is not prudent to repair the cast stone in the same fashion, or the same unwanted results will occur again.

 

Refinishing Cast Stone Material

 

Throughout this bulletin, we have tried to convey the possible reasons why cast stone material deteriorates, flakes, chips, separations, and erodes. Proactive, preventive care, proper manufacturing, proper installation, and continued maintenance are better precautionary tools than any restorative solutions.

 

Proper ingredients used to mix the cast stone material, proper water concentration, proper tamping and casting, proper curing, proper storage, proper installation, proper reinforcements, proper cleaning, and proper water repellents are essential. Continued maintenance and care is cheaper and more successful than restorative measures. Proper jointing, sealants, and mortars must be considered especially when weather consideration, extreme temperatures and movement are taken into account. Proper consideration and preventive measures must be taken for excess moisture and water runoff and collection, especially around the base of buildings and planters.

 

Cast stone material is very difficult to re-tool, grind, or sand blast, and may prove to be impossible without breaking the cast stone or damaging it. Depending on the aggregate used, re-tooling and grinding may discover that the original aggregate used was too large and coarse.  Fine lines and decorative designs may also be an impossibility.

 

When sandblasting the cast stone, bigger aggregates may chip or crack off and ruin the finely sculptured design that you desire. Since you would probably be using a sticky pattern mat for the sand blasting or painting, you may find that what little sticky nature the matting may have to it, it may pull the fine surface layer of the older cast stone material off.

 

Re-tooling, grinding, or sandblasting may make matters worse if the cast stone were manufactured with the added fine layer of sculptured design. The process may intensify the chipping, scaling, separation, and flaking due the vibration and movement of the outer surface.

 

Trying to match the historic coating of the cast stone material surface with today’s cement, sand, admixtures, and pigments may not prove advantageous and will probably not result in your desired effect. Since separation is the reason that the outer layer needs replacing today, separation should be the concern, eventually. Additionally, this type of coating may be counter-intuitive as it may trap moisture in the cast stone units and eventually be the cause of future outer surface chipping and cracking.

 

Older methods of staining and coloring of cast stone are a fine art. Replicating the older artwork may not be successful or longlasting. One must make themself very familiar with using colors, pigments, stains, and paints.

 

As an example, tea-staining is an older method of staining stone. One must find someone that is exceptionally familiar with the staining method as cast stone is very porous and applying a tea bag to the cast stone will leave an unmistakable dark mark—wanted or unwanted. If unwanted, the color is dark, and very difficult to remove or hide.

 

In conclusion, it is prudent to seek professional advice when attempting to restore any structure that has cast stone material. Ingredients of yester-year, as well as the processes used have changed, and matching the style, technique, design, colors, and layering may be impossible thus making replacement your only option.

 

If you choose to do any repair on your own, we suggest that you attempt to try the repair technique and coloring on an inconspicuous spot. Remember that wet cast stone patching will be darker than the older, drier areas, and may take up to a year or more to match the coloring. Additionally, weather, staining, and aging of material will probably be impossible to match for any expert in the cast stone industry. We can do our best to match color and texture, but age will play an important factor in the blending of the older with the newer pieces.

 

Remember to always take necessary precautions to protect doors, windows, decorative trims, and grade materials from any work that you attempt. Should you wish to wash the stone, confirm that you have considerations in place for water run-off. Completely rinsing the cast stone in water and confirming that any collection of water does not hold any acidic mixture in it for any length of time is important. Make sure that you use only the pressure from your water hose. Do not use high-pressure equipment or sandblasting to clean the cast stone.

 

There is so little one can do to change the appearance of cast stone once one commences repairs. Careful planning and research is essential.

 

CARE AND MAINTENANCE —DETERIORATION, AGING, AND REFINISHING (PDF)

 

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.