Polyurethane Resins
  Why has my polyurethane part delaminated?
 

Thick-walled parts, built up in several pours, can delaminate if one of the layers has cured too much before the next layer is poured.

The second and subsequent pours can usually be made between 3/4 hour and 1 hr after the previous pour.

Delamination may occur if the original surface is moist or greasy, not allowing it to bond with the subsequent layers.