Different materials, different movement
A gunite shell, a concrete deck, stone coping, and ceramic tile all respond to temperature differently. Bond them rigidly together and something has to give at the weakest point — usually the tile bond or the grout.
That is what the expansion joint between the deck and the coping is for. It is a deliberate gap filled with flexible mastic so the deck can move independently of the pool.
When that mastic fails — and in Texas sun it fails on a schedule — the deck and the shell start fighting each other directly, and water gets into the gap.
The mastic joint is the highest-value cheap maintenance on a pool
Failed mastic lets rain and splash water run behind the coping and under the deck. In expansive clay, that water swells the soil, then it dries and shrinks. The cycle lifts and drops the deck.
Symptoms: coping stones that rock or have popped up, a widening gap you can drop a pencil into, tile falling off just below the coping, and deck cracks running perpendicular to the pool edge.
Redoing mastic is inexpensive. Repairing the coping, tile, and deck damage that follows years of neglect is not. If you do one preventive thing on the structure, do this one.
Tile, waterline, and freeze
Waterline tile sits exactly where water, sun, and freezing air all meet. It gets thermal cycling from both directions plus scale from hard water plus mechanical stress from any shell movement.
Hollow-sounding tile means the bond has already released. It will come off eventually; the only question is whether it does so during a freeze and takes grout and substrate with it.
Aggressive descaling — especially on natural stone and softer tile — is specialist work. Doing it wrong destroys the finish permanently, which is why calcium removal gets referred to a professional who does only that.
Decks and the clay underneath
Central Texas soil shrinks in drought and swells with rain, and pool decks are large flat slabs sitting on top of it. Hairline surface cracks are normal; cracks that widen, offset vertically, or continue into the shell are not.
Extreme summer surface temperatures also matter for use, not just durability — dark decking and some stone become genuinely unsafe to walk on barefoot in August.
Watch drainage. Deck water directed toward the pool edge instead of away from it accelerates every problem on this page.
What to inspect each spring and fall
Run a finger along the expansion joint. Missing, cracked, hard, or pulled-away mastic goes on the list.
Tap along the waterline tile and listen for hollow spots.
Look for coping stones that move, grout that is missing, and any new crack you do not recognize.
Check that deck drains and scuppers are clear before the rainy stretches.
Photograph anything questionable so you can compare next season. Movement over time is the diagnosis; a single photo is not.
