Just curious how others specify installation of large format wall tile (porcelain) … and by large format, I’m talking tile that is 16 inches x 24 inches in size.
Thanks!
TCNA 2012 says W231/W241-12 “for areas where wall flatness is critical, such as when tiles with any edge longer than 15 inches are specified.” (it’s a mortar bed installation with bond coat, optional waterproof membrane, mortar bed, scratch coat, metal lath, & cleavage membrane, over wood or metal studs). Mortar bed thickness is 1 inch over metal studs and maximum stud spacing is 16 inches o.c.
Since I almost always cite TCNA installations, I wouldn’t mess with anything else unless the tile manufacturer said this is wrong and gave a guaranteed alternative - and even then I’d want to know why.
Cute photo!
To facilitate a tile installation that will meet ANSI finish requirements the substrate must meet the following subsurface tolerance. For tiles with at least one edge 15 in length, maximum allowable variation is 1/8 in 10 from the required plane with no more than 1/16 variation in 24 when measured from the high points in the surface. Mortar coverage for ceramic tile for dry areas is 80% and for wet areas is 95%. Mortar coverage is to be evenly distributed to support edges and corners. Key mortar into the substrate with the flat side of the trowel. Comb the notched side of the trowel in one direction. Firmly press tiles into the mortar and move them perpendicularly across the ridges forward and back to flatten the ridges and fill the valleys. Periodically remove and check a tile to ensure proper coverage is being attained.
you should consult with the tile manufactures to discuss grout joint size, tile and pattern selections that will minimize issues relating to flatness and lippage.
Big problem maybe getting a flat wall for a thinset application. I like the idea of doing a mortar bed, but I hardly ever see this anymore. If you do that, make sure your designers take the increased thickness into account for accessibility requirements.
I’d contact the folks at Custom Building Products, Mapei or Laticrete. All three make good large-format, medium bed mortars that should work well. I’d use this over cement board as you’ll get a better bond. Using a medium bed mortar will help take those pesky tolerances out of the equation which will be a problem otherwise. If this is a wet area, waterproofing membrane will be needed.
Check the bond strength of the products being considered.
I would steer clear of thinset mortars and organic adhesives. Epoxy setting systems may work, but I’d check out the medium bed mortars first.
Depending on the size and height of the wall, do not overlook to check the structural strength of the supporting wall. On a couple of occasions, I have needed to decrease the stud spacing or stiffen the stud.
The Division 09 section for non-structural metal framing should include performance requirements for deflection such as L/360 or whatever is recommended for these large format tiles. We delegate the design of the non-structural stud gage and spacing. Gages shown are minimum, spacing shown are maximum.
For example:
1.3 SYSTEM DESCRIPTION
A. Structural Design:
- [Structural design of [overhead] non-structural lightgage metal framing systems shall be furnished by the Contractor.]
- Select framing systems, gages, supports, bracing, and connections as necessary to meet the structural requirements specified.
- Partition framing shall conform to the widths indicated, unless approved otherwise. Provide thicker gages and decreased stud spacing as necessary to meet the design requirements.
- Select framing members based on the manufacturer’s published span tables.
B. Design Loads: - Interior Ceiling Assemblies: 5 pounds per square foot uniform live load, plus dead loads.
- Exterior Soffit Assemblies: 30 psf positive and negative uniform live load, plus dead loads.
- Interior Partitions without Wall Mounted Casework: 5 pounds per square foot uniform live lateral load.
- Interior Partitions with Wall Mounted Casework: 5 pounds per square foot uniform live lateral load, casework dead load, and casework live load of 25 PSF of shelf area.
- Seismic Loads: Conform to the requirements of currently enforced edition of the jurisdictional code authorities.
C. Deflection Requirements: - Maximum deflection of L/240 for flexible finish materials such as gypsum board and veneer plaster.
- Maximum deflection of L/360 for rigid finish materials including gypsum plaster, cement plaster, ceramic tile, maximum 3/8" thick stone tile, or mirrors.
I hope to see some or all y’all in Phoenix. I will be wearing the Hoss cowboy hat with a red maple leaf pin in front.
I’m not sure if L/360 is stiff enough. The BIA recommends L/600 to prevent cracking in brick veneer over steel studs.
These large size tiles are more sensitive to wall deflection than plaster or more conventional size tiles. Thus you may want to consider even tighter criteria.
Some of the glass mat products also have weight restrictions so make sure to comply with the manufacturers restrictions as well.
Thanks much for the great input and food for thought!!!
I always recommend the mortar setting bed as the installation method for oversized tile but get resistance at times so I’ll be passing this along to our designers.
If you are instaling the tile in a public space you might consider eliminating the steel stud, lath, membrane and backer board issues altogher by placing the tile on CMU. This is not always an option and you do need to make sure the mason builds a flat wall but it can take away a lot of the deflection worries (assuming the structure can handle the wieght)as well as being more damage tolerant.
I have seen many installations where all of the extra attention and work associated with making a stud wall perform as needed for a large format tile installation could have been just as easily (and cheaply) acheived by hiring a mason.
The main problem (aside from the extra room needed for the wall) is the range in CMU widths permitted under ASTM standards. If the non-tiled surface can take the variation (as much as 3/8 inch if memory serves me correctly), then this strategy may work well. Otherwise, you may have to parge the wall to float it to level. At this point you may have wished that you did the stud wall.
I don’t think true mortar bed is needed. Thin-set medium bed is probably fine. Brick veneers are much more sensitive, I think, to deflection because minor cracks can turn into major leaks, which is not an issue with interior construction in a dry environment. Mortar manufacturers make non-sag formulations to help with installation. Even then, the weight of these large tiles will make a good job a challenge. Variation in flatness is not so much of a problem on walls because no one will trip on it. You may, however, see it if the lighting is at a low angle. Another thing to consider is that not all tile is particularly flat corner-to-corner, and this may show shadows as well.