What 40 Years at Blue Bell's 358 Foot Elevation Does to Expansion Joints, Tile & Concrete
A pool shell, its expansion joints, and its tile bond coat all move slightly with every change in temperature. They expand when the surrounding material warms and contract when it cools. This movement is normal and expected, and a properly functioning expansion joint is designed to absorb it without transferring stress to the tile or concrete nearby. The amount of movement in any given cycle depends directly on how wide the temperature swing is during that cycle. A bigger swing means more movement. A smaller swing means less.
Blue Bell’s position at 358 feet above sea level means the community experiences wider temperature swings between summer highs and winter lows than the valley communities in the Schuylkill and Wissahickon corridors below. Each annual thermal cycle at this elevation covers more temperature range than the identical cycle at a lower elevation.Â
The expansion joints, tile bond coat, and concrete on a Blue Bell pool move slightly further during each cycle than the same components on an identical pool at 150 feet would move. Over a single season, that difference is barely noticeable. Over 40 or more years on the pools from the 1970s and 1980s that make up most of Blue Bell’s residential stock, that small additional movement per cycle accumulates into a measurable difference in total structural stress.
This is why the repair findings we see on older Blue Bell pools follow a recognizable pattern. Expansion joints that have hardened and lost flexibility transfer their absorbed movement to adjacent tile and concrete. The tile bond coat in that area weakens and tiles loosen. The concrete nearby develops cracks at the point where the stress concentrates without a functioning joint to release it.