Page 10 - Demo

10 Flooring Specialist Summer 2026FLOOR PREPNot that long ago, a concrete slab was a typical concrete slab. You showed up on a job, ran your moisture tests, did your prep and installed the floor. There were variables of course, but for the most part you knew what you were dealing with. That%u2019s changing. Across the country ready-mix producers are quietly shifting to Portland Limestone Cement, also known as PLC or Type IL. In many markets it%u2019s already the default, yet most flooring contractors aren%u2019t being told. So you walk onto a job thinking you%u2019re dealing with a traditional Portland cement slab%u2026and you%u2019re not. That%u2019s where things can start to go sideways.Same Concrete%u2014Different BehaviorLet%u2019s get one thing out of the way: PLC isn%u2019t some experimental material. Structurally, it performs. Engineers are comfortable with it. Concrete contractors are placing it every day. But from a flooring standpoint, it doesn%u2019t always behave how you%u2019d expect. The biggest difference? PLC mixes tend to hold onto moisture longer. They can create tighter, denser surfaces and don%u2019t always follow the same drying patterns contractors have relied on for years. In other words, the rules haven%u2019t changed%u2014but the assumptions have.The Moisture TrapHere%u2019s where most problems start. You walk a slab. It looks and feels dry. The schedule says it should be dry. But when you drop probes in, the RH is still high. That%u2019s not unusual with PLC. These slabs can achieve strength on time (which keeps the job moving), but internally they%u2019re still holding moisture. If you%u2019re installing resilient, wood or anything moisture-sensitive, that%u2019s a problem waiting to happen. And if you%u2019re relying on how things %u201cusually%u201d dry, you%u2019re left guessing. What contractors are learning the hard way: You can%u2019t shortcut moisture testing anymore. If anything, PLC makes proper RH testing more important, not less. And it means being ready to push back when the schedule doesn%u2019t match the slab conditions.The Surface Isn%u2019t What It Used to BeAnother thing you%u2019ll notice is the surface. Some PLC slabs finish tighter, smoother and less porous. That might seem like a benefit, but for adhesives it can be the opposite. If the surface is too dense, you don%u2019t get proper adhesive wet-out or penetration. So that bond you%u2019re counting on is already PLC Concrete: The New Reality Under Your FeetBy Jeffrey B Johnson, MAPEI FCIS business & marketing managerPhotos courtesy of MAPEIcontinued >>>