Historic natural stone, tile, and masonry, such as floors and walls, architectural features, statues, fountains, monuments, and the like can become damaged with use or exposure to the elements. When professional attention is necessary, it is important to select a qualified contractor who not only has the knowledge, skills, and training to work with your natural stone, tile, or masonry, but who also understands historic conservation methods and employs responsible preservation practices. At Set in Stone Restoration, we do our research and ask the appropriate questions to gain a clear understanding of our client’s expectations before we write specifications or prescribe treatments for historic surfaces. Then, we perform the work according to the plan, and in most cases, we are able to achieve the desired outcome for your marble, granite, travertine, slate, onyx, limestone, and more.

Four Approaches to Historical Stone Restoration

We can customize our services to address concerns and resolve problems while staying within the standards addressed by the Secretary of Interiors Standards for the Treatment of Historic Properties. These standards specify four approaches, beginning with the gentlest means possible and progressing to more aggressive methods:

1. Preservation emphasizes repair and maintenance of the surface as it is rather than restoring or reconstructing it to its original appearance.
2. Rehabilitation recognizes that in order to accommodate continued or new use, a surface may need to be repaired, altered, or added to without altering the historic character of the surface. Of the four approaches, this is the most flexible.
3. Restoration means accurately depicting the character of a surface as it appeared at a particular historical time period. It may involve removing added features or reconstructing missing features.
4. Reconstruction involves new construction of non-surviving portions of a surface to replicate its appearance at a particular historical time period.

To aid the reader’s understanding of these approaches, we will use a hypothetical polished terrazzo floor as an example. Suppose the floor has developed a patina over time. One area has minor damage, say, a small chip. Another area has some pretty major damage, for example, a section of terrazzo is missing. The original floor had a honed finish, but back in the 1950s someone had it polished. The now-polished terrazzo is covered with fine scratches, dirt, and scuff marks.

To preserve this terrazzo floor, our goal would be to remove the dirt and scuff marks. We might begin by cleaning with plain water, and if necessary, use a professional pH-neutral cleaner or a mild alkaline solution and a soft bristle brush. We would make no attempt to remove the scratches, repair damage, or replace the missing terrazzo.

To rehabilitate this terrazzo floor, we would first attempt to achieve the desired result using the gentlest means possible. If the outcome were not acceptable, we might lightly hone the terrazzo, removing only .0008 inches of material (an insignificant amount). This would remove the 1950s polish and make the appearance of the floor more closely resemble that of the original historical appearance. We would make no attempt to repair damage or replace the missing terrazzo.

To restore this terrazzo floor, we might clean and lightly hone and use tinted filler and matching aggregates (historically accurate mixes) to fill in the small chip. We would make no attempt to replace the missing terrazzo.

To rehabilitate this terrazzo floor, we would clean, hone, and repair the chip, but regarding the major damage, we would likely either consult with a stone conservator, depending on the difficulty level, availability of appropriate materials, etc., or refer the client to a stone conservator.

Diagnosing Problems

Exposure to water or moisture, light, chemicals, foot traffic or use, and other factors can have a negative affect on natural stone, tile, and masonry surfaces. The most common problems are the accumulation of dirt and grime, scratches, dullness, chips, and cracks. Here are other problems you may encounter:

• Efflorescence is a deposit of soluble salts on the surface. It appears as a powdery white haze.
• Subflorescence is a potentially harmful accumulation of soluble salts under or just below the surface. Once pressure buildup is sufficient, spalling or delamination may occur.
• Spalling is a breaking off of the surface layer.
• Delamination is a peeling of the surface layer.
• Detachment is cracking that has turned into a clean break.
• Sugaring is a granular disintegration of the surface.
• Weathering is roundness, smoothness, or loss of detail.

Solutions

At Set In Stone Restoration, we employ the most appropriate methods to resolve historic natural stone, tile, and masonry problems. We always protect the surfaces surrounding our work area. Following are some of the solutions we use.

• Cleaning with plain water, in some cases, can be very effective for safely removing dirt and stains. Whether we are wiping, gently flushing, or using a low-pressure continuous spray, we always use great care.
• Cleaning agents are used only when plain water will not suffice. Our cleaning solutions may include organic surfactants, pH-neutral cleaners, and alkaline or acidic cleaners followed by neutralizers.
• Abrasives are usually avoided. On the rare occasion that we feel an abrasive may be necessary, we will consult with other experts for confirmation and guidance.
• Crack repair may involve stabilizing the crack to prevent further damage and/or doing cosmetic repairs.
• Chip and hole patching is performed using historically accurate filler mixes and painstaking precision to blend the repaired area with the surrounding surface.
• Replacement is using materials matching as closely as possible to the surrounding surfaces. Replacement services are performed under the guidance of a stone conservator.

A Note on Historic Buildings

Historic buildings are notorious for developing structural problems, plumbing failures, and other age-related problems. Sometimes we make recommendations for extraneous problems to be resolved prior to doing our work. For example, if a building has a moisture problem that is causing efflorescence, the moisture problem must be resolved first, and then the efflorescence problem can be resolved afterward. If we removed the efflorescence only, the problem would just reoccur.

A Note on Polishing Historic Stone

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