Here is a sbs on how to make zimmerit using Milliput. It was a lot easier than I thought it would be once I got past my fears.

Step one:
I laid out everything I needed to do the zimmerit. I got a clean flat hard surface, in this case a cutting mat, a small cup of water, a small amount of flour (Talc powder can be used also), something to roll the putty with (I used the handle to one of my large exact o knives), a exact o knife, a paint brush (for the water), a sanding stick, Milliput (2 part epoxy, I used the gray and white kind), zimmerit tools (Lion Roar), a spreading tool, and the piece to be zimmed. For the spreading tool I simply took some spare styrene and cut it into two different sizes to help in small and large areas. I filed an angle on the edge of it also.

Step two:
Cut equal sized pieces of each part of the epoxy. Knead the two parts together until it is one solid color and no streaks can be seen. It is important to keep your fingers moist during this time or the putty will crumble into tiny little pieces.

Step three:
Know comes the fun part. It helps if you have been around, or have it yourself, making biscuits because this step is vary similar. I laid some of the flour (or talc powder) on the cutting board and rubbed some on the rolling device. It is important to keep flour under the putty and on the rolling device at all times because you have to get the putty pretty thin, and if the flour is not on there, it will tear the putty to pieces. I rolled it as thin as I could, almost paper thin.

Step four:
Next, I took the sanding stick, a course one, and scuffed the areas receiving the putty. I then cut out a size close to the area I wanted to cover. I took the brush and put water on the model, and also on the side of the putty that will be touching the model. I placed the putty on the model. I made sure my fingers were wet and I pressed the zimmerit in place and around the details. I used my knife to cut around some details and also cut the excess putty from the top and bottom. I used the spreading tools, dipped in water, to smooth out the surface and get rid of my finger prints. This small tool is also helpful for getting it around the small details.

Step five:
When all the surfaces were covered that I planned on zimming, I took my zimmerit tool and dipped it in water. It is important not to do too much at one time, and also to only do one side. This is so the putty does not set up too fast and also so you do not ruin pieces you already did by over handling the model. For this project I chose to do one side and the front and back of the turret. After the zimm tool is nice and wet, I started doing the pattern in the large areas. I pressed it hard and went back and forth over the areas to get nice deep ruts. Here is my own opinion, so take it or leave it. I have looked at a lot of pictures of zimmed vehicles in preparation of this build. I found a really nice King Tiger with zimm on it and it had some great up close shots. One thing I have noticed on all these is the irregularity of the patterns. I think too many people, and the pre zimmed kits, have the zimm in nice even rows, and it looking nice and smooth and even all over. It was not. It was applied much like stucco is applied with a trowel and then the pattern was scored in there. Now I know I used a tool that they did not use, but that is why I overlapped areas and did not make straight lines. Again, this is just from my observations, and I did not even pull it off totally right, but I wanted a random look, and I think I got it. Anyway, while you are doing this part, either with a tool, Tamiya pe tools, or a screw driver head, make sure to keep them wet so the putty will not stick to it. Also keep the putty from building up the tools. I use an old tooth brush to run over the tool now and then.

Step six:
Time for some more fun. Hopefully at this point you have decided what your finished model is going to look like and how much damage is going to be on it. Keep in mind, zimm was similar to concrete, so it chipped easily if shot with small arms or brushing against things. In other words, if your finished model represents a tank that has been around for any amount of time, it will have damage to the zimm. How much? That is up to you. It is just easier at this stage to do the damage because the putty is still able to be cut. I went along with a sharp knife and cut out areas either of battle damage or wear.

Now that the zimmerit is done for the session, let it sit for at least 24 hours or more. Do other areas the following session, and then go back a couple sessions later to finish the sides you missed before. This will give the putty ample time to set up and be able to handle without fear of damaging it. After all the putty if fully cure, you can sand down any rough areas. You can still add more damage, it will just be harder because the putty will be rock hard. Once you are ready to paint, just lay down a primer coat before you paint the main colors to make sure everything is uniform for the base coat. I use Tamiya surface primer or Mr. Surfacer 1200 for my priming.

Here is what the final product looks like.