I tested out a Salt Weathering technique for chassis weathering that I thought some of you guys might appreciate. This is not an original idea. I've seen military aircraft guys use this to simulate random patchy camouflage paint on modern Navy aircraft, and armor guys use it to simulate rust under peeling paint. I recently watched some Dr. Cranky videos on Youtube and he was using this technique to simulate a grungy chassis on a post-apocalyptic zombie hunter type vehicle. That got me to thinking that it could be used to simulate a muddy chassis on a 4x4 that I'm building.
This is my first attempt at this, so I decided not to risk ruining the model I'm building. Instead I mocked up an approximation of a ladder vehicle chassis with some scrap sprue. The floor pan is a sample credit card from the junkmail and the front and rear suspension are a spare set from one of those Revell "Donk" kits.
With the test mule assembled, I sprayed the whole thing with flat black Krylon right from the spray can. After about an hour, I airbrushed two shades of dark gray (Tamiya Nato Black and Testors Engine Gray) lightly around the chassis. Leaving more protected the top of the chassis darker and spraying the lighter gray more on the more weathered areas areas towards the ground like the bottoms of the frame rails and the bottoms of the axle and suspension.
I let that dry a couple days, and in the mean time bought some fresh salt (the stuff I had on hand was gummy from moisture and would not work).From all the research that I did on the subject, it seemed that I would need some fine and some course salt. I picked up these two at Walmart for right at $2.
I poured equal amounts of the two salts on a piece of paper and mixed it together. I then I wet the chassis with a spray bottle filled with warm plain tap water and started sprinkling the salt mixture around just pinching it in my fingers and just carefully dropping it all over. I heavily salted the chassis, especially the top areas that may not get as much mud and dirt. I let that dry overnight and then airbrushed some dark brown randomly around from the bottom (though I did hit the tops of the axle and suspension).
After the dark brown dried, I wet the chassis again with warm water and sprinkled another layer of salt. Then I went with a lighter brown. I did this four times working my way down to a tan color.
This picture shows after my third layer. It was saltier than a ballpark pretzel by that time.
After the last coat of tan dried, I took a stiff toothbrush and scrubbed off the salt. I got 95% off that way, but some salt was left in the nooks and crannies. It actually looked a lot like some small pebbles and dirt clods were stuck up in the recesses and I may choose to leave my model that way. However, just to see what would happen, I rinsed the assembly under warm water in the sink and that was all easily washed away.
Here's the final result. I don't think it came out half bad for a first effort. (sorry about the poor pictures, my camera wasn't cooperating with me).
BTW, the paint I used was cheap craft paint. I've wanted to test using this in an airbrush for a long time now so this was a good opportunity. To thin it, I poured some Liquitex Airbrush medium in a small cup about 60% full. I then took a craft stick and added a small amount of craft paint to the mix until I got it about the consistency of 2% milk. I made it a little too thick at first, so I added some Testors Acryl universal thinner to one of the mixes as well, but it wasn't really necessary. All you really need is the Liquitex Airbrush Medium to thin it.
I wouldn't want to use this as a primary paint, but for weathering I think it works very nicely. One of the complaints about craft paint is that it isn't very durable on plastic. For weathering I think that is actually a benefit. Mud and dirt are not durable either. They are easily wiped or washed off, so if the weathering gets rubbed off on the high spots from handling, it actually makes it look more realistic. When I am finished with my weathering, I'll seal it all in with some Future mixed with Tamiya X-21 flattening agent. You could also mix some of that mixture in with the craft paint as you airbrush it to increase durability.
Edited by dmk, 18 September 2013 - 09:07 AM.