I've heard several different reasons why they stopped using zimmerit. The ones stated above, as well as that the Russians started using anti-tank weapons instead of magnetic mines. Cold have been a combination of all of them, I guess. One of those OBE things!
I've done pe zim and used the Polyester Putty method mentioned above. I do not care for pe zim (at least, not on 1/35th scale. On 1/72, it's probably okay). First, it doesn't have enough relief to it. Second, there are gaps between the edges of pe pieces.
As far as the putty method goes. Tamiya Polyester Putty is about twice the cost of Squadron Green or White putty, but you get about twice as much, so I think it workds out about the same. It's a two part putty and the set up time depends on how much hardener you mix in with the putty. I keep putting less and less in. It still sets up pretty fast. Not nearly as fast as does Squadron, but faster than I'd like, most of the time. It also (to me) has a much stronger oder than Squadron putty. One thing thats really good about it is you can sand/scrape it off it you don't like it. It's also relatively easy to chip it off areas where it got accidently (i.e. weld seams).
Another couple of products that you might want to consider are Zimm-it-right. I'm not sure where you can get this stuff. The other is called Apoxi-Sculpt and it's available from R&J Enterprises. They are both supposed to be great stuff for doing zimm. Their "set up" time is in the hours, rather than minutes. I haven't tried either one, as yet.
If you decide to zimm something, find some good ref pictures on the zimm pattern used and where on the tank it was applied. Especially if you're doing a specific tank. For instance, on a Tiger I, some tanks had zimm on the front, lower hull between the fenders. Many didn't. (I found this out the hard way, right after I'd zimmed that part of my Tiger Mid Production!!)
Good luck with it.
Bill
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DML M4A2 Red Army
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-- There is a fine line between "hobby" and "mental illness". (Author unknown)