#MAPEITechTip: What are Specialty Mortars—when are they appropriate?

As we discussed in a previous blog, “How do you know you have selected the ‘right mortar’ for the ‘right tile or stone application’?”…polymers both dried & liquid latex, have dramatically changed how we set tile today—improving bond and mortar’s ability to move and deform as a complete system in both interior and exterior applications. 
 
However what if you need additional features, like a mortar with a quick-turn-around time? Typically these type of mortars are formulated utilizing calcium aluminates cement instead of traditional Portland-Based cements, these cements have special properties that provide resistance to corrosion, abrasion and heat combined with rapid hardening and early compressive strengths.  On a fast track project, these types of mortars will typically permit grouting in as little as 3-4 hours—additionally these mortars do not contribute to efflorescence. 

What are the challenges when installing glass tile?  Like porcelain tile, glass tile has even less texture and porosity, making it a challenge for the adhesive to ‘grab’ the back of the glass tile bond it both chemically and mechanically to the substrate.  What about the color of the mortar itself—have you ever seen a glass tile installation that just didn’t seem to pop and sparkle? Due to the translucent properties of glass tiles (some stones can have this same issue), the color of the mortar can dramatically affect the end result of your glass installation—thusly the birth of ‘Ultra white’ mortars. (See ANSI A137.2)

What about moisture sensitive stone (i.e. e.g.: rosso levanto)—can these be set with traditional Portland-Based mortars?  The stone manufacturer will typically indicate the best adhesive to use with their stone—depending on its susceptibility to curl or warp while the mortar hydrates when exposed to moisture.  If it is unknown whether a stone is moisture sensitive or not, a dimensional stability test will need to be performed to determine the stone’s susceptibility to warp, curl and discolor.  (A Dimensional Stability Test, as noted in the photo, uses a damp piece of felt against the stone tile’s surface while measuring the movement of the stone over a specified amount of time)  If the test determines that a traditional mortar (set time >24 hours) can’t be used due to a stone’s moisture sensitivity, a rapid-setting calcium aluminate mortar ( > 6 hours) can often be used.  The same rapid-setting properties that will allow a fast-track installation, will may also allow installations of a moderately moisture sensitive stone tile, to hydrate more quickly lowering the risk (curling, warping and discoloring) of moisture contact with the stone.  Always do a mock-up board if it is unknown whether or not the stone is moisture sensitive.  It the stone curls, warps or discolors, it will then be necessary to set the stone with a reaction resin, like an epoxy or polyurethane adhesive.  Since these adhesives are ‘reactive’ (exothermic) and use no water, there is no risk of warpage or curling like either traditional or calcium aluminate mortars. These epoxy mortars also work well when setting on suitable metal surfaces such as in elevator cabs and steel stair treads. 
 

Let’s address one more installation—mixed media. What do you do if you want to install tile or stone insets in a glued-down wood flooring installation? Is it necessary to stop and switch to a cementitious mortar?—depending on the adhesive manufacturer the urethane can be used to simultaneously set both at the same time.  Since this blog involves specialty installations, it is always important to check with both the tile/stone/glass and mortar manufacturer for specific recommendations and limitations.