Zimmerit: History and How-to
How To - The Putty Texturing Method
The best method for modelling zimmerit in scale is by texturing putty. Here is a description of how to do it. Study some good photographs to see what small variations are specific to the vehicle, such as how the pattern forms around hull fixtures.
The photograph to the right shows my Tamiya Pz.IV Ausf.J with Zimmerit applied using the textured putty method. I used plastic putty, in this case Squadron's Green Putty and R&J Product's Zimm-it-rite, (which are the light grey areas). The Zimm-it-rite was the superior of the two materials because it had a much longer working time -- hours as opposed to minutes as for the Green Putty. Also, since it does not attack the plastic, it is very forgiving, Zimm-it-rite can easily be washed off before it sets. I recommend Zimm-it-rite as the best material for modelling Zimmerit.
So, using putty, either Green Putty, Milliput or Zimm-it-rite, I recommend the use Zimm-it-rite however, follow the steps below to produce an authentic and in scale Zimmerit pattern. I wrote this description with Zimm-it-rite in mind, but I have noted differences in brackets for plastic putty, and for other epoxy putties the techniques should be the same.
Determine which details to fix before or leave off until after the zimmerit is applied. Generally small parts such as tools, headlights, mufflers, etc., should be fixed after, while parts that are integral to the hull such as Saukopf mantlets are best fixed before the zimmerit. Using the reference photographs as a guide, pencil in some guide lines. This may seem pointless since you will obscure the lines with putty but they do help you visualise the finished plate as you are working on it, thus keep the pattern consistent. If damaged zimmerit is to be shown then these areas should be masked off now. I use ordinary masking tape. Be sure to check reference photos to see how real zimmerit falls off too.
The surface should be washed to remove grease and then roughened up with coarse sand paper to give the Zimm-it-rite something to grip. This roughening up step is the key to a good Zimm-it-rite application, (for plastic putty: you can skip this step since solvent based putty dissolves the plastic).
It is quite easy to fix stowage, tools and such on after the Zimmerit is applied if small squares of 0.015" sheet stock are glued to the points were these fittings are fixed to the hull. If you look closely at reference photographs you can see that this is actually how the tool racks are fitted, so there is a space between the hull and tool rack, (especially on Panthers). The putty is spread just thick enough to leave the tabs showing - after texturing the fittings can be glued directly to these tabs; referring to fig.1 below, note the tabs are circled in red. Also, just to be on the safe side, its a good idea to mask any areas where zimmerit is not supposed to go.