Monday, May 23, 2011

Technical Info - new additions to the 2011 TCNA Handbook

This week’s Technical Advisory deals with one of the unique new additions to the 2011 TCNA Handbook – specific installation methods that pertain to the installation of dimensional stone.

Recall that “stone” in the 2011 TCNA Handbook is defined as:

“Natural stone tile, also called dimension stone, is stone that has been harvested from its in-situ position in the Earth and cut and machined into tiles without altering the natural fabric of the material. Dimension stone has a nominal thickness of less than ≤” (19mm) and does not have any facial dimension greater than 2’ (610mm). Agglomerates and other engineered products do not meet this definition and therefore are excluded. Natural stone tiles that meet the definition but not the dimensional requirements are also excluded.” - 2011 TCNA Manual – Natural Stone Tile Selection and Installation Guide page 13.

For a refresher on natural stone tile characteristics and installation tips, reference the Natural Stone Tile Selection and Installation Guide located on pages 13-17 of the 2011 TCNA Handbook.

A note of importance contained within the Natural Stone Tile Selection and Installation Guide concerns “fiberglass mesh reinforced stone”. This note can be used to back up our position on the use of epoxy adhesive with stones backed with epoxy or polyester. The note states: “Many stone products have a mesh reinforcement adhered to the back surface of the tile. The adhesive used to attach the mesh is not standardized, but is commonly an epoxy or polyester-based adhesive that Portland cement mortars will not reliably bond to. Such reinforced stone tiles require epoxy bonding mortar.” An exclusion to this caveat is a specific stone / backing that has been tested and approved to be used with a latex fortified Portland cement based adhesive.

Another item that is need of clarification is the deflection criterion associated with stone installations over floors. The Marble Institute of America requires the following deflection criteria (MIA Design Manual):

Concrete slabs – not to exceed L/360
Plywood / Wood Framed Constructs – not to exceed L/720

Bear in mind that LATICRETE has established a deflection criterion not to exceed L/480 under total anticipated load for “stone” installations for both walls and floors (except when building codes take precedence). This LATICRETE requirement covers both dimensional stone as defined by the TCNA (above) and engineered stones. In addition, the L/480 criterion takes into account the variability in stone hardness and flexural strengths. Many stones may not have the flexural strength / integrity to be installed on slabs that meet L/360 deflection criteria. Therefore, LATICRETE’s more rigid requirement of L/480 covers the instances where these conditions may apply.

Also, it is important to note that all of the thin-bed stone installation methods require a tighter substrate surface tolerance of 1/8” in 10’ from the required plane when measured from the high points in the substrate surface.

EXTERIOR FLOORS – pages 198 - 205

Exterior Floors – (Stone) - pages 198–200
Exterior Roof / Deck Floors (Stone) – pages 201-203
Exterior Balcony / Deck Floors (Stone) – pages 204-205

A simple concept to keep in mind is that all of the exterior floor methods that apply to ceramic tile also apply to stone applications. There are a total of 5 methods that cover the three exterior applications under EXTERIOR Floors. This will not be the case with the INTERIOR Floor methods.

INTERIOR FLOORS – pages 206 – 230

Interior Floors Over Concrete – (Stone) – pages 206 – 221
Interior Floors with Radiant Heat Over Concrete – (Stone) – pages 222 – 225
Interior Floors with Radiant Heat Over Wood – (Stone) – pages 226 – 227
Interior Floors Over Wood – (Stone) – pages 228 – 230

Most of the common installation methods that apply to ceramic tile applications are covered in the stone section. Chemical resistant installations and methods that utilize organic adhesive are not suitable to receive stone as a finish and are therefore excluded.

Stone installation methods over wood framing are limited. There are 3 methods in the handbook over wood frame construction:
F250 (note that this method erroneously states L/360 maximum allowable deflection, it should be L/720)

However, method F250 allows for the use of various backer board types as the underlayment in addition to multiple combinations of plywood underlayment / backer board types.

Some common notes / requirements for the stone methods are as follows:

The stone methods factor in an additional 2lbs. weight per sf when compared to the ceramic tile details.
Consider unsanded grout for soft or semi-soft stones such as limestone, travertine, marble, onyx, or similar.
Cementitious Bond Coat – use white (colored adhesive mortar) for light colored marble, limestone, and other stones where staining or darkening from grey setting materials is possible.

Next week we will discuss vertical stone installation methods. Please let me know if you have any questions or concerns.

Arthur Mintie
Laticrete International
Technical Services Director

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