Point 1: Choose the right stone for the right project.

As we know, there are many different types of stone with various finishes and backings that are available in the marketplace. Always use the correct type of stone and finish for the appropriate application. For example, don't use a very soft and porous type stone (e.g. sandstone, limestone) for an entranceway or lobby floor to a store, office building or airport. These types of stones are better suited for vertical work or in areas that will experience less traffic. The finish is also important in these areas. Honed or thermal finishes many times are the better choice for high traffic. These finishes may also better comply with the slip-resistance requirements of commercial projects. Polished finishes can be limited to accent pieces on floors or for use on vertical applications. Also, consider the density of the stone when choosing a product. The denser the stone, the better it will wear.

Point 2: What is the application?

A few questions concerning the application require answers before the installation can be specified and can commence. Is the application interior or exterior? If it is in an exterior application, will it be exposed to freeze / thaw conditions? Will the stone be exposed to continuous underwater submersion or intermittent water exposure? Is it a vertical or horizontal application? These questions demand answers, since these answers will have a direct bearing on the choice of installation products and even the type of stone and finish. For example, if the stone will be installed in an exterior application or a submerged application, the installation products must be suitable and not degrade in these environments. All installation products are not created equally. Some installation products can handle these applications, while others cannot. Consult your adhesive manufacturer for more information on which installation products can be used for your specific application.

Point 3: Is the stone gauged to an even thickness?

If it is, then it can be installed in either a thin-bed or medium-bed method of application. An evenly gauged stone will be relatively easy to install in these methods of installation. As a rule of thumb, if the stone varies more than 3⁄16 inch (4.5 mm) in thickness, it should probably be installed using the thick-bed method of installation. A medium-bed mortar should be able to accommodate any irregularities up to an irregularity of 3⁄16 inch (4.5 mm). If a mortar bed is required, then the stone should be installed in the wet set method, meaning that a bond coat is applied to the fresh mortar and the stones are beaten into the fresh mortar to the desired height.

Point 4: Check the back of the stone.

Take a look at 10 different stones. You may be surprised to see how many stones have various types of backings on them. These backings may be composed of polyester or epoxy backings with fiber mesh scrims, or they may have another thinly cut stone laminated to the back of the “main” stone. These backings are also designed to provide rigidity and to stabilize some of the more fragile stone types used on floors. However, these backings can possibly present some challenges to the installer. First, contact the stone supplier to see if they have any special instructions from the manufacturer that provides direction for which type of adhesive mortar should be used for the stone that they supply. In many instances, the backing on the stone is some sort of resin backing. More often than not, it should be installed in an epoxy-based adhesive. Also, check to see how well the backing material is bonded to the stone itself. It makes no sense to use a high-strength adhesive mortar just to have the backing peel away from the back of the stone. Some manufacturers of these types of stones will broadcast sharp sand or other aggregate into the resin to facilitate a better mechanical bond with the adhesive mortar. However, if there is a question as to the ability of the adhesive mortar bonding to these resin backings, it makes sense to be on the side of caution and use an epoxy adhesive mortar.

Point 5: Why should a crack suppression membrane be considered?

Considering the investment that is being made with using stone as a finish material; it makes sense to want to ensure that it stays looking beautiful for years to come. Using a crack suppression membrane to either treat existing hairline or concrete shrinkage cracks will help to prevent the transmission of these cracks through to the stone finish. In addition, using a full floor treatment in an effort to guard against future potential cracks also makes sense when one considers that these materials generally add about $1.50 per square foot to the installation. When factoring what the cost is to replace cracked stones, the initial investment in a crack suppression membrane is obvious. The use of a crack suppression membrane should be considered if the installation includes an electric radiant or hydronic heating system. The membrane will help to prevent any cracks that may result from the thermal cycling of the heating system. The cycling of the heating systems could cause some hairline cracks to occur in the setting system that may potentially transmit through the finish layer.

Point 6: Use a waterproofing membrane in wet areas.

If the installation will be made on an exterior building face or in a water feature or in the bathroom and shower areas, a waterproofing membrane should be used to protect the occupied spaces around the application. Stone is not waterproof in itself; a waterproofing membrane must be specified and used in these applications. In addition, if the application is an exterior project over occupied space, further precaution is needed. In these instances, a primary roofing membrane should be used first and then a setting bed with a draining layer should be used. Reference the industry standards for these unique applications. It's important to keep in mind that water damage still remains one of the biggest threats to stone applications. It's important to use an appropriate waterproofing membrane in these applications.

Point 7: Prepare the substrate.

There is nothing worse than specifying a beautiful stone and then seeing a horrific installation where there is lippage and an uneven flooring finish as the end result. Preparing the substrate is key. Industry standards require that the substrate will not vary more than 1⁄4 inch in 10 feet. In some cases, when using a polished stone or a large-format dimension size, tolerances should be even tighter to reduce the reflection of lights or sunlight on a floor. Usually 1⁄8 inch in 10 feet is required for these types of finishes. Another point to consider is to make sure that the substrate is rigid enough to support the stone and the installation system. The use of high-strength patching materials and self-leveling underlayments can be used to make the substrate comply with these industry standards.

The Marble Institute of America (MIA) requires that deflection of substrates should not exceed L/720 when stone is used. In addition, concrete slabs should be cured and dry enough to receive the installation.

In today's fast-track construction, moisture-related issues are becoming more commonplace. Usually, a reading of 75 to 85% concrete relative humidity (using a hygrometer), or 6 to 7% moisture content of concrete (using a moisture meter) or 5 pounds per 1,000 square feet (using a calcium chloride test) are good indicators that the concrete is dry enough to receive the installation.

Point 8: Use good adhesive mortar and installation practices.

Once the substrate has been prepared and the appropriate membrane is in place (if applicable), the installation of the stone itself can commence. Good installation techniques should be followed when installing the stones. For thin-bed and medium-bed installations, this includes using the appropriate-sized notch trowel and back troweling the stones to ensure complete bedding of the stones with no voids. It is always a good idea to periodically pull up a freshly installed stone to verify the coverage and mortar transfer. All of these methods and practices are all the more important if the stones that are being used are thin and fragile. The thinner the stone, the more effort is required to ensure a good installation. Use a high-strength, latex-fortified, thin-bed or medium-bed mortar for the best performance. These mortars achieve high-shear, tensile and compressive strengths. They are also shock and vibration resistant. They are ideal for use in today's commercial buildings. In some cases, if the stones are moisture sensitive (usually green marbles and some agglomerates), a 100% solid epoxy adhesive mortar should be used to prevent curling or warping of the stones. In addition, use a white-colored adhesive mortar for light- or white-colored stones. Some installers will only use a white mortar regardless of the stone color to avoid confusion on the project site. The use of a white mortar will prevent darkening of the stone, which could change the overall appearance of the entire installation. Always honor expansion joints that may exist in the substrate and bring them through the stone finish. Movement joints should also be placed at the perimeter of the installation as well as in the field. A good rule of thumb is to follow the Handbook for Tile Installations (TCA) guidelines outlined in “Expansion Joint Detail EJ171.” Although this is a tile industry publication, the MIA also points back to this detail in their installation manual. Use a suitable flexible sealant that is non-staining and will hold up to the traffic and maintenance that the area will see. Note that most acrylic-type colored caulks are not suitable for these installations.

Point 9: Selecting an appropriate grout for stones.

As for the finishing touch, the grout used should really complement the stone installation. Most of the problems that occur with stone installations are related to the grout, whether it is color consistency or durability. A compatibility test should always be performed on the stone with the grout that will be used. Some stones may require that sealer be applied to the face of the stones to make the grouting and clean-up process easier. Some stones may be stained by the grout, if the sealer precaution is not followed. If a Portland cement-based grout is chosen, the use of a high-quality latex-fortified grout is always a good idea. There have been great strides with new products in this area. For even better performance, there are now new types of grouts that can be used with stone that will not experience all of the typical inherent problems that Portland cement-based grouts do. Some of these products include a unique cross-linking technology grout and various epoxy-based grouts.

Some of the advantages to these cross-linking technology grouts and epoxy grouts are as follows:

They contain no Portland cement, which can lead to efflorescence or mottling and other color problems associated with Portland cement-based grouts.

These grouts are very dense and have an extremely low porosity rate, which makes them extremely resistant to staining.

• They provide uniform color - reducing color shade variations.
• They are very durable - will not crack or peel.
• They are easy to clean and maintain due to their smooth texture.
• They never require a grout sealer.
• Generally, the grout is as dense and durable as the stone itself.

Point 10: Follow the stone manufacturer's maintenance regimen.

Once the installation is complete, it's time for the stone to do its thing: look beautiful for many years and to provide the high performance that we have all come to expect. In order to ensure that the stone does this for a long time, it's important that it be taken care of in accordance with the manufacturer's or supplier's maintenance guidelines. This includes using any required sealers and cleaners. Usually, a neutral pH cleaner should only be used with stone finishes. In commercial environments, a maintenance prescription can even be written by the supplier to ensure optimal performance.

Conclusion

The use of stone in commercial environments is continuing to rise. It is one of the most versatile building materials known. To ensure that it is specified and installed correctly, these 10 points will help to avoid common mistakes and problems that are associated with stone installations. It is our goal to continue to increase the per capita consumption of stone. The way to do this is to ensure that stone is successfully installed, so that commercial building owners will consistently demand stone as a finish material for years and years to come.

Arthur Mintie is Director of Technical Services at Laticrete International, Inc. He can be reached at www.laticrete.com or 1-800-243-4788.