Static cracks versus moving cracks
Most shrinkage cracks in a residential slab are static. They formed as the concrete cured and are not going anywhere. Those fill permanently. A crack that is still moving seasonally, often from settlement or frost, will telegraph through any repair. We look for offset between the two sides and staining that indicates ongoing movement.
Why rigid rather than flexible filler
A flexible caulk stays soft and the coating over it deflects and splits along the line. A rigid polyurea cures harder than the slab, so the repair carries load across the gap and the coating sits on a continuous surface. It is counterintuitive but it is what the material science supports.
Control joints are a different decision
Control joints are deliberate cracks. They can be filled flush for a seamless look on a stable interior slab, or honoured through the coating on a slab that is still moving. That judgement is made on site rather than from a price list, and a contractor who does the same thing everywhere is not making the call at all.
When to walk away from coating
Structural cracking with vertical offset between the sides, or cracking that has appeared and widened recently, indicates a slab or subgrade problem that a coating cannot address. In those cases the honest answer is to investigate the cause first, and we will say so.
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