When a moulder packs green sand into the drag and cope, the sticky clay binder makes the two halves want to fuse. A thin layer of this fine, dry, binder-free sand is sprinkled over the joint line before the top half is rammed. This ensures the mold can be cleanly separated to remove the pattern.
Heard on the job
Dust a little more parting sand around the deep pockets or the cope will pull chunks out of the drag when we lift it.