Beyond the Basics: How Additives Like HPMC & RDP Boost Tile Adhesive Performance What makes some adhesives excel in these areas while others fall short? The answer often lies in two key additives—HPMC and RDP—and a few other unsung ingredients that turn basic glue into high-performance adhesive. Tile adhesive is not just cement and water—it's the additives that turn basic glue into a high-performance workhorse. In my latest article, I break down the unsung heroes behind strong, workable, weather-resistant tile adhesive. HPMC acts as the "regulator" that buys you time to adjust tiles (keeps adhesive from drying out too fast) and no more sliding! RDP is the "bodyguard" that fights humidity, frost, and aging—critical for tropical or cold climates. Plus the supporting players of additives that prevent cracks, fix pinholes, and boost flexibility. Skip these, and even the strongest adhesive might fail fast.