With the filler applied to...
With the filler applied to the entire surface of our enclosure, we wait for the "green stage."
Properly mixed body fillers should have approximately 10 minutes of working time before beginning to set. If this is your first project using body fillers or a specific brand, I recommend mixing a small test batch, without applying it to the project, and use a stopwatch to see how long it takes to set. This will give you a reference for how much hardener should be added to the filler. Different types and brands of filler require different amounts of hardener for proper working times. Some reinforced fillers will not fully cure if sufficient cream hardener is not added, while too much hardener will not give you enough working time. Be sure to thoroughly and completely mix the hardener with the filler (for at least 30 seconds) to avoid having soft or uncured areas. Creating a smooth shape with body fillers takes time and practice. Applying a smooth coat can help reduce grinding and make things easier, but is not critical at this stage. Cutting the plastic spreaders to custom shapes can help ease spreading. The spreaders can be cleaned with acetone and reused.
The basic shape is quickly...
The basic shape is quickly smoothed out using 36-grit sandpaper during the "green stage."
Although I usually apply the reinforced filler and allow it to cure overnight without touching it, those of you without access to compressed air or air tools will want to take one more step before calling it a day. Instead of allowing the filler to become rock hard before sanding, sit there and wait for it to reach the "green stage." Don't call your girlfriend, don't have a beer and don't go to the bathroom (if you must go, go really quickly!), because you might miss your golden opportunity to save a lot of sanding time. After the filler sets and completes its exothermic reaction (in which it heats up and starts cooling back down), it reaches a stage when it can be easily sanded using 36-grit sandpaper. If the filler "rolls" off with the sandpaper, wait a little longer until it sands off like grated Parmesan cheese. Taking the time to knock down the high spots, spreader marks and rough areas during this "green stage" will save a lot of time and effort later. Next time we will cover the finishing stages of our composite enclosure.
Tools and Supplies:
Automotive Upholstery Store:
Light colored speaker grille cloth
DuoFast TI-3118A pneumatic upholstery staple gun w/ 3/8" crown x 3/16" or 5/32" 22-gauge wire staples
Home Improvement Store/McMaster.com:
36- and 50-grit sandpaper
As the application R&D supervisor at Alpine Electronics from 1995 to 2003, Chris Yato was in charge of creating and managing numerous demo vehicles that served as centerpieces at CES. All of them have been featured inthis magazine. He is currently the special projects manager/fabrication trainer for Competition Soundworks in California. E-mail him at chris@teamcsw.com.