Wargaming Basics of polyurethane casting

So. You want to cast wargame terrain in polyurethane, but it seems like a mess to get into.  Well, you are 100% correct. 

But it is a hell of a lot of fun once you start creating. It's what being a hobbyist is all about. About six months ago, I began scouring the web for video tutorials and product reviews for casting compounds. I knew I was planning a big wargaming table (the promethium reactorum), and I wanted to do a lot of things that were presented in the tome of 40K wargaming: the Forge World Imperial Armour Masterclass. 

After experimenting with several products and techniques, I want to give you the basics that I've learned, and some of the best products that I've found. The picture below shows my garage work station (It's an old chunk of an Ikea desk on a cardboard box). I suggest setting up a place to work that is at least 5 feet away from anything valuable, especially if you are just learning.  Also, the chemicals you may be working with have dangerous odors and irritants, so a well ventilated garage or outside space is best.

In the picture above, you'll see a roll of paper towels, face masks appropriate for small particulates, a pair of cutters, a plastic cutlery knife, plastic cups, some rubber molds (Woodland Scenics Rocks) and a green thing in a yogurt container (more on that later). The yogurt container is quite good for serving as a container for your mold, and I use the Fage greek yogurt pint container with a flat bottom on the inside.  

If you want to make your own mold, and cast parts from it, you'll need both the 2-part mold-making silicone rubber, and the 2-part polyurethane.  I absolutely love the products made by Polytek, and I couldn't endorse any company more strongly. They have great videos online, they make a wide range of really great products, and they really have great customer service.  Even better, you can order from Amazon (in the US) or just order online directly (I suggest ordering directly, since they give a steep discount on your first purchase). If you are casting solid plastic parts for terrain building, I suggest the products pictured (EasyFlo 60 and PlatSil 73-25), as they worked great for me. One down side was that they use FedEx and for me this caused a bit of a problem, because the UPS guy tends to be a bit better about delivering products without explicit signatures.

If you are using rubber molds (like Woodland Scenics), you will absolutely need a mold release agent.  If you try to skip this to save a couple bucks, you'll destroy your molds within a few casts. Basically, without the release agent, the polyurethane adheres to the mold. I found that Mann 200 (below) is the best for this. I've had one spray can that has lasted over fifty casts, and the molds are still in good shape. Now, to be honest, I'm doing castings of rocks, so the detail is not so important.  If you plan to cast things with tiny details, you may have to pay more attention to the molds over time. 

If you are using silicone rubber molds, you don't need a release agent. That's the advantage of making molds yourself.  The rubber Woodland Scenics molds are actually intended for casting with plaster, which I think is too heavy for what I wanted, but they worked great for casting in polyurethane as long as you use the mold release spray. 

Below are a couple examples of the cast rocks. One thing to note is that you don't want to waste the polyurethane. Therefore, you should cast rocks as thin as possible. This is actually very simple: starting with only a little bit of the mixed liquid plastic, as the polyurethane is curing and becoming more viscous (which only takes about 1-2 minutes) you will want to tilt the mold around in your hand to let the liquid flow around and create a thin shell of the rock mold.  This will make the cast thin, which is also good for breaking it up for more varied rocks. You'll be able to see the curing process, as there is a critical point where the liquid suddenly changes to a white semi-solid polyurethane (science is awesome).

Below is an example of something I cast up for the promethium reactorum. I used the original part and glued it to the bottom of a pint sized yogurt container.  Then, I mixed up the PlatSil (which comes as a 2 part yellow and blue = green) and very slowly poured it around the part. I learned a lot about this process from Youtube videos produced by PolyTek and others. For this part, I used just enough to fill the PlatSil to the very top edge (leaving the piece you see in the yogurt container). This is the mold. 

For the second half of the part (pictured at the lower half of the picture), I first cast a small part using Blue Stuff. Blue Stuff is another cool product that allows you to 'press-mold' into a soft heated piece of polymer (much like athletic mouth guards). You can find a lot of Youtube videos on this product as well. Once I made an original, I then glued it to the bottom of another yogurt container, and poured the PlatSil over it, forming a level and flat mold shown below.

Again, you don't want to waste a lot of the polyurethane, so it doesn't make sense to make a big heavy solid cast. Instead, for the part I show below, I used a hollowed out cardboard tube with masking tape and thin plastic from a plastic sandwich bag to seal the bottom of the cardboard tube. Once I poured the liquid plastic into the mold (filling only half way), I then plunged the cardboard tube down into the mold. I waited 1-2 minutes for the cast to cure partially, and then the tube is fixed in the mold. Once the cast is solid, I then cut off the excess cardboard tube using the HackZall (see my first post ever for details about this awesome tool).

Voila! Let me know if you have questions. It's a fun process, with a bit of a learning curve. But, if you are in to big projects, it's really good skill to know, particularly come the apocalypse.