How Clay Moves Under Slabs
Alabama red clay expands significantly when wet and shrinks when dry. That cyclic movement stresses the slab from below, producing typical hairline shrinkage cracks and occasional structural movement.
Impact on Coating Choice
Small shrinkage cracks are cosmetic and easy to seal before coating. Active structural cracks need to be identified — a rigid coating over a moving crack will telegraph the crack.
What We Do About It
- Chase and fill hairline cracks with structural polyurea before coating
- Use semi-rigid fillers on active joints so the coating flexes with them
- Watch for cove-line cracking around slab perimeter (expansive clay signature)
- Recommend structural assessment when we see excessive movement
Long-Term Reality
A well-installed floor can flex enough for typical Alabama clay movement. Aggressive movement — from poor drainage, plumbing leaks, or foundation issues — needs to be addressed structurally, not coated over.