Stone damage, such as spalling and cracking, that is too great to repair in situ may need full replacement. In cases where a portion of a stone unit is damaged and the stone is hard to match, it may be able to be partially replaced with a dutchman repair.  

• Vertical Panels – Stone panels can be directly adhered to a wall substrate in select circumstances, depending on the weight, overall dimensions, and configuration. Wall substrate flatness is critical for a successful installation and must fall within a tolerance of 1/8 inch variation in every 10 foot and not greater than 1/32 inch between each stone panel. Each panel should be fully back-buttered to achieve 100% adhesive contact between it and the substrate. Bond should be tested to confirm adequate adhesion of the panels to the substrate. 

• Flooring and Stairs – Floor panels are 100% back-buttered with a cementitious bond coat, set in a dry-pack mortar bed and tamped down until true and level. The dry-pack mortar bed can be bonded or unbonded to the concrete sub-slab. Membranes are also commonly used to isolate cracks in the concrete sub-slab, reduce moisture transfer, or when joints in a concrete sub-slab do not match up with joints in the stone flooring. Stone stair treads and risers are set in a solid mortar setting bed. Depending on the design, anchorage may be required.  

• Countertops – Stone countertops are required to overhang from their supports. The thickness of the stone slab will vary based on supporting details. Countertops are usually fabricated by the stone supplier in the required size and shape as dictated by the design. Adhesives are typically used to attach the countertops to their supports and may require shims in some applications. 

Joint spacing and allowable lippage are based on stone dimensions, surface finish, and installation. For very large panels, joint spacing can be adjusted to minimize lippage. Joints between stone units are typically a minimum of 1/16 inches wide and filled with sanded or unsanded cementitious grout or sealant. Unsanded joint fillers are typically used for narrow joints and stone panels that are softer or have a polished surface. Cementitious grouts can be polymer modified to reduce moisture permeability and increase flexibility. Specialty sealants are also available that are mold and bacteria resistant for wet areas. Any material used to fill stone panel joints must be non-staining to avoid discoloration along the joint edges often referred to as haloing. Accelerated leach/stain testing is recommended for the selected stone and joint material. 

Localized interior stone damage, such as chips or spalls, can be repaired in situ using resinous patching compounds that are epoxy, polyester, acrylic, and/or urethane based. The type of patching compound is selected depending on its properties and application. Viscosity, UV-resistance, curing time, hardness, and abrasion resistance all impact the appropriateness of patching material. These compounds can be color-matched in the field by skilled craftworkers to match the existing color and translucency of stone, as well as sanded down and polished to a high shine. 

Crack repair options depend on the size of the crack and unit stability. Hairline, surficial cracks can be filled with an appropriate penetrating adhesive. Deeper or through-body cracks typically require patching and anchorage, or replacement and reconstruction if the stone unit has cracked into multiple pieces. If cracking is caused by structural instability or issues with original installation, the unit may need adhesive injection under a flooring unit or resetting and regrouting.  

Stone flooring that has severe scratches, scuffs, or coatings can be resurfaced and restored to its original appearance. For calcium carbonate stones that don’t polish well, crystallization is a chemical process that can be used to bring the surface to a high shine. Depending on the thickness of the stone unit, it can be resurfaced many times before replacement is necessary.  

Abrasion resistance and slip resistance are important properties to consider when choosing a type of stone flooring. The amount of foot and equipment traffic as well as proximity to outdoors will determine the level of abrasion resistance necessary. Slip resistance is necessary for the safety of building occupants and is determined by the dynamic coefficient of friction (DCOF), interior environment, building use, and slope of flooring.  

Resin impregnators are often applied during fabrication to stone slabs that are later highly polished, most commonly those that are used for countertops. Resin impregnation aids in the aesthetic uniformity of surface polish by filling cracks, fissures, and tiny voids in the natural stone. Impregnating water repellents are a separate class of impregnators applied post-installation and are often referred to as sealers. Though commonly used, these types of impregnators aren’t needed to protect interior stone surfaces. Impregnating water repellent may be helpful on highly porous stone or in areas where staining potential is high. Any impregnator chosen should be compatible with the specific type of stone present.  

Daily dust mopping and vacuuming reduces grit that can act as an abrasive, helping preserve the stone surface. Cleaning up spills, damp mopping, and wiping down stone with warm water helps prevent deep staining over time. For floors, regular cleaning with a pH neutral stone soap and removing stains with stone poultice reduce the need for more aggressive cleaning or restoration. Abrasive cleaning treatments that damage stone surfaces are inappropriate and can leave stone walls and floors open to accelerated weathering and lower resiliency. 

With repair and restoration projects, it’s important to understand the properties of the existing stone system, material properties, and anchorage prior to selecting replacement materials and repair strategies. The following field and laboratory testing may be needed for interior stone evaluation. 

FIELD TESTING:

• Water Penetration 

LABORATORY TESTING:

• Compressive Strength, Density, Porosity 
• Abrasion Resistance  
• Slip Resistance