Tuesday, August 24, 2010

Adhered Thin Stone Wall Cladding Installations

As a Stone Consultant and Stone Contractor in Florida, and particularly South Florida over the past 30 years, I have observed many improper installations by local subcontractors. In particular, adhered stone installations for wall cladding using the spot bonding method (be it 4 spot, 6 spot, etc). Based on my experience any stone or tile adhered directly to the substrate should follow ANSI tile installation standards which require 80% coverage on the back of the tile for interior surfaces except showers which should be 95% and exteriors at 100% coverage.

In many cases even thick stone (3/4” or 1-1/4” thickness) has been installed using a variety of bonding mortars and also spot bonding methods but using no means of mechanical anchorage on interior walls as well as exterior walls. Many times the Owner, Architect or General Contractor are not aware of the proper installation methods and accept a low cost alternative to a mechanically anchored system.

Industry Installation Standards

MIA – Marble Institute of America - Dimension Stone Design Manual
ANSI – American National Standards Institute – Standards for Installation of Ceramic Tile
TCNA – Tile Council of North America Handbook for Ceramic Tile Installation

The MIA Design Manual recommends using only ¼” to ½” thick stone up to heights not to exceed 15’-0”. The size of the stone panels should not exceed 36” in the longest dimension or be more than 720 square inches in total area. The weight of each piece should not be more than 15 lbs. per sq. ft.

The MIA endorses the use of some of the installation methods detailed in the TCNA Handbook for Ceramic Tile Installation for installation of stone tile. The methods endorsed for wall tile installations are W201, W202, W211, W221, W222, W231, W241, W243 and W244E. For stone tile walls directly adhered to concrete or stable masonry surfaces with thinset mortar W202 is the required method. Please note that a waterproof membrane is required for all exterior installations. TCNA method W215 Spot-Bonding Epoxy for ceramic tile, is as of the date of this writing not endorsed in the MIA Design Manual for adhered stone. The TCNA refers to the epoxy manufacturers specifications for ceramic tile installation instructions using this method. Also of note, movement joints are always mandatory per Method EJ171, as detailed in the TCNA Handbook (see below).

Movement Joints - Vertical and Horizontal

Especially important to a successful adhered wall cladding installation are the placement of movement joints. The TCNA Handbook establishes the guidelines for movement joints as follows. Interior movement joints should be placed 20’ to 25’ in each direction. Exterior movement joints should be placed 8’ to 12’ in each direction. Also, interior tile work exposed to direct sunlight or moisture should be placed at 8’ to 12’ intervals in each direction. Please note, in areas where the stone tile is spanning different materials such as concrete columns or slab lines to adjoining masonry walls or other changes in backing materials, such as gypsum board, then a movement joint is also necessary. Basically, a soft joint should be located where any dissimilar materials meet since they have different rates of expansion and contraction as well as differing movement as a result of differential movement of the building structure.

Substrate Tolerances

When adhering directly to the backup substrate it is important to inspect for tolerances of the substrate and proper preparation by other trades. The MIA requires a more stringent tolerance for the backup substrate than the TCNA does for a ceramic tile installation. The MIA requires the backup to be within 1/8” in 10’-0” of the required plane for thinset stone veneer where the TCNA requires the backup to be within ¼” in 10’-0” for installation of ceramic tile in thinset mortar.

Joint Size

Another important consideration for an adhered stone tile installation is joint size. Optimum joint size should be considered relative to the size of the stone tile and the stone tile fabrication tolerances in order to mitigate the appearance of lippage. Lippage, an installation tolerance, will be covered in an upcoming Blog Post.

Typically, and in accordance with the MIA Design Manual guidelines, exterior stone wall cladding should have joints that are ¼” width minimum but 3/8” preferably. For larger size exterior wall panels ½” wide joints are frequently required depending on inherent warpage and stone fabrication tolerances. Interior stone wall cladding should have joints that are 1/16” minimum but preferably 1/8” in width depending on stone fabrication tolerances and inherent warpage. For large panel size units ¼” or larger width joints are required frequently. Tight, hand-butted joints should not be used under any circumstances.

Mesh Backing

Depending on the type of stone material used you may come across stone tile panels with fiberglass mesh reinforcement applied to the back side of the tile. This reinforcing mesh is embedded in an epoxy or polyester resin. This method of backing is generally used to reduce breakage and make handling safer when working with large slabs of fragile stone. However, please be aware that cementitious materials, such as thinset mortars, will not adhere properly to epoxy adhesives. Only compatible epoxy adhesives should be used that provide the required bonding strengths to the fiberglass and epoxy backing you are bonding to. It is interesting to note that a well known manufacturer of epoxy stone adhesive has specific requirements for removing any epoxy and mesh backing down to the bare stone where you will be using their adhesive to bond to the back of the tile. This should be done using a mechanical wheel grinder with a diamond blade before application of their epoxy stone adhesive.

Please let me know if you think this post was helpful and any other information you would like to share regarding your experiences.


  1. This is a great post Ed. I emailed a copy to my office computer so I can share it with others. I've completed a few jobs with a stone epoxy and spotting. I read the part about it not being a MIA recommended installation. Is that because of the need for a further review or because of perceived problems? I'd be interested to know.

  2. Pat,
    Welcome and thanks for the comments. Please share this information with your readers. I would be interested to learn how you came to visit this Blog.

    To answer your question, my blog entry states that TCNA method W215 Spot-Bonding Epoxy for ceramic tile is not listed in the MIA Design Manual as an endorsed installation method. This does not necessarily mean there are any "perceived problems" with that installation method. Since this method is relatively new compared to the mechanical anchorage methods there is less of the installation method history. My mention in the blog concerning the epoxy spot bonded method was meant as cautionary advice for installers. As stated in the TCNA manual concerning this method Installers should follow the manufacturer's installation instructions and recommendations. At some point in time the MIA may endorse or issue an update or bulletin with their comments relating to the epoxy spot-bonding method for natural stone.

    Thank you for your interest in this Blog.

  3. Ed,
    I think that I came over from a post on Linkin in the MIA Group.

    We're about to do another small job using the epoxy spot method. These are interior applications, and we do use the manufacturer's recommendations as you mentioned.

    We've been happy with the outcome so far using the epoxy spots. Like any setting system though, reasonable caution is advised. We try to stay away from pushing the system.

    Best regards,

  4. Have you ever seen 18" x 36" x 3/4" thick, 10 lbs square foot, limestone tile installed on an ICF house vertically up to approximately 25' high over stucco brown coat with heavy mesh thinsetted with no mechanical fasteners? I am being asked to do this with approximately 4000 sf of stone.

  5. flmac1961 I personally have not installed stone at the sizes you mention with the direct adhered method. I would prefer to use mechanical anchors with relieving angles at 15' intervals.

    As stated in this blog post above

    "The MIA Design Manual recommends using only ¼” to ½” thick stone up to heights not to exceed 15’-0”. The size of the stone panels should not exceed 36” in the longest dimension or be more than 720 square inches in total area. The weight of each piece should not be more than 15 lbs. per sq. ft."

    Your 3/4" thickness would exceed the 1/4" - 1/2" recommendation of the MIA. Also your height of 25' would need to be relieved at the 15' level. If there was a failure an independent expert might point this out and you would be at financial risk. The overall dimension and weight per piece seem to be within the maximum allowances of 15 lbs per sq.ft. and 720 sq.in.

    There are always new setting materials coming out that exceed past limitations. You might want to contact manufacturers such as Laticrete and others that may have recommendations for this installation and provide a warranty with their specific products and setting methods.