[wdb]

I think you mean 'kleien' instead of 'klaaivormen'?

[com]

I’ve heard “kleivormen” in Hoorn, “klei maken” (a little more gross - no surprise given their famous export, disease swearing, I suppose) in Den Haag, and “kleien” below the great rivers.

Edit: spelling, never ran into the NL word for clay in writing as an adult language learner not into geophysics, civil engineering or pottery