I took this picture in the Caen museum in Normandy…it shows how thin the actual zimmerit was, and how it gets battle damaged from glancing shots…
Also some more battle damaged zimmerit…
These 2 are from some before and after shots outside Mortain, I will be posting in my Normandy thread…I have pictures of the same spots today.
I believe the Zimmerit, from the steel surface of the tank to the tops of the ridges, was a little over 5 mm. (of course it could vary + or - a millimeter.) That would be slightly more than .25".
The Zimmerit on the two Panther tanks was museum-applied post war.
You are indeed correct…I had to Goggle it.
Does not matter for the discussion. The other pictures show the original zimm thickness is the same thickness as the reapplied zimm. It looks like the zimm pattern is a series of ridges and valleys. The valleys look to be about the same level as the armor surface leaving the ridges to be the thickness you are actually looking for.
Less, not more 
0.25 inches is 6.4 mm. Though 6 mm is also “a little over 5 mm”.
Per the instructions reproduced in Spielberger’s Sturmgeschütze: Entwicklung und Fertigung der sPak,[1] Zimmerit was to be applied in a “thin” layer (no actual thickness mentioned), left to dry for four hours, next hardened with a blowtorch and then a layer approximately 4 mm thick added, into which ridges were stabbed with a putty knife. That would, at a guess, result in a total thickness perhaps twice that of the layer actually applied?
3rd edition; Stuttgart: Motorbuch Verlag, 1997; ISBN 3-613-01356-8 ↩︎
Are you taking into account “shrinkage”? 
Unavoidable in the fall mornings and winter months…or after a cold shower!
