A couple people have asked me for tutorials on how to use bondo-glass, and I know there are more than a few people out there that have never used any kind of bondo at all. What better time to do a tutorial than while working on my own armor.
First off, here's a list of things that I use.
1 can of Bondo-Glass
1 can of regular Bondo
2 tubes of red cream hardener
1 peach-colored scraper-style Bondo applicator (i'll explain this in a minute)
80 grit sandpaper
160 grit sandpaper (or something close)
320 grit sandpaper
1 rubber sanding block (for the 80 grit sandpaper)
1 razor knife (any kind of razor knife will do)
Something flat, smooth, and hard to mix the bondo and bondo-glass on. I used 1/8" posterboard.
Step 1:
Use the 80 grit sandpaper, and rough up the plastic pretty good. This is important, so take your time and make sure you get everything, specifically the edges.
Step 2:
A. Open the can of bondo-glass and use something to stir it with. It's dark green, stinks like hell, and will have some oil sitting on top of it. Make sure you mix it up very well.
B. Once it's mixed, use your scraper to get enough out of the can to completely cover your piece of armor. Don't use too much, or it will just be wasted. Close the can back up when you've got enough on your mixing board.
C. Open one of your tubes of hardening cream, and squeeze it out across the top of your bondo-glass. The directions on the can say that if you use 1/4 of the can, squeeze out 1/4 of the tube. If you don't use enough, it will take longer to harden, and won't be as hard when it's cured. If you use too much, it will set VERY QUICKLY, but it will be very very hard.
D. Use your scraper to mix the bondo-glass and hardener. There really isn't a trick to this, you just get faster at it with practice. Scrape it all off your board, and then spread it back onto the board. Repeat this until you have an even color throughout the bondo-glass, but don't take too long. The minute you mix the hardener in, the clock is ticking.
E. Load your scraper up with bondo-glass, and apply it to your armor in a clean stroke. Don't worry about making it nice at neat at this point, just aim for 100% coverage. After you've got it all covered in bondo-glass, continually smooth it down with your scraper, paying attention to edges and corners, until it starts to get a grainy consistance, and doesn't smooth out anymore. At this point, just put your armor piece down on something, and use your razor knife to clean off your scraper. The bondo-glass should be tacky, kindof sticky-feeling, and should come right off your scraper. You can throw it away and use a new one next time if you want, but if you're on a budget (like me), clean off your scraper first, then your mixing board. Once that's done, the bondo-glass on your armor should feel warm... that's the chemical reaction between the bondo-glass and the hardener. At this point, you can also use your razor knife to trim the rough spots along the edges, and any globs or raised spots. Don't go too crazy with it, but you can clean it up pretty good with a razor.
Step 3:
Give it about 20 minutes to fully cure, and you can start sanding it with the 80 grit sandpaper. I recommend using the sanding block entire for this part. You'll have to use a good bit of pressure at first to get through the top layer, but once you do, it's pretty easy. Try not to go all the way through to the plastic, but if you do it's not a big deal. I used my dremel to do my rough sanding at first, then the sanding block to smooth it out after that. If you use your dremel, take your time. One slipup could mess you up pretty good. Or be a nice weathering feature.
When you've got it sanded down to the point where there are minimal low spots throughout, and the edges are pretty uniform, bust out the 160 grit sandpaper and go over it by hand. You can use the sanding block if you want to, but I do it by hand. Try to get rid of the scratches created by the 80 grit paper. Again, take your time on this and focus on uniformity. You're not trying to remove material at this point, just to smooth out the deeper scratches from the 80 grit.
Step 4:
A. Set your piece aside (I recommend washing it in cold water to remove all the particles from sanding) and pull out your can of regular Bondo, which is a light grey color. Using the same method you used for the bondo-glass, mix it up first, then scrape some out on your mixing board. You won't need nearly as much as you did the bondo-glass, because this is only for filling in the little pits and scratches that are still in the bondo-glass.
B. When you mix in the cream hardener, which is red, the end result should be the same color as the bondo scraper. That's one of the reasons I use those, so I know when I've got the right amount. Put in more hardener if it's too light a color, or more bondo if it's too dark. When it's mixed, it will be a much creamer substance than the bondo-glass.
C. Using your scraper, apply the bondo in a thin, even coat over the entire surface. Again, focus on 100% coverage instead of neatness at first. Once it's covered completely, just as before, continue to smooth it down until the consistance starts to get grainy.
D. This is when you can again clean off your scraper, mixing board, and work area. When that's done, trim the excess bondo off your piece with your razor knife. Don't trim too much, just the excess.
E. Take out your 80 grit sanding block again, and work on smoothing it all down to an even coat. Regular bondo sands much easier than bondo-glass, and is also VERY dusty.
F. Once you've got it all sanded uniformly, use the 160 grit and again work on sanding out the scratches left by the 80 grit. Work on getting your sides and edges nice and crisp, unless you're going to make battle damage.
G. When you've got it sanded nice and smooth with the 160, bring out the 320 and work on making the surface feel like glass. It helps to wash the piece off in cold water after finishing with the 160, before you use the 320. The sand particles will be the consistance of talcum powder or confectionary suger, so if you're married, and you choose to do your sanding inside (like I do), make sure you're away from anything that will get covered in this very very fine powder.
Step 5:
Now we're ready for primer. Use whatever color primer you want, I use white wet/dry sandable primer on mine. Apply the first coat evenly, but not thickly. Wait an hour or so for it to cure completely, then apply a second coat just like the first one. Again, wait an hour to cure. If you use rough primer, use the 320 grit paper to sand it smooth. After priming, apply your base coat of paint. I used two coats of metallic silver paint because I'm going to try the layered weathering method.
What you do at this point is up to you.
Make sure you're in a well ventilated area when you use the bondo-glass and bondo... you'll see quickly that it smells real bad. I don't know how harmful the fumes are, but it stinks pretty good.