I have built a custom box out of fiberglass. I would like to try to clear some things up. After it is all done with the glassing part I add Bondo. After I add the bondo I sand and add more bondo and sand again. When is it enough Bondo (how many layer should I need to do)? I have started my sand ing with a 60 grit and then going to move to a 220 grit, 400,600,800. I have noticed after the 60 grit that there very little pits. Do I need to refill with Bondo before I continue or just keep sand or what? Also I was sanding in some spots the I sanded all the bondo away and the glass is coming though. It is smooth, do I need to redo this area as well or that is fine like that? You can see this box here.
https://www.cardomain.com/memberpage/529247/2 . I took off the purple cover. No pics of Bondo yet.
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Body filler isn't used to add thickness, but to fill in any spots. I usually use around 36-40 grit paper for my shaping. Then when the shape is perfect, I apply a last thin layer of body filler, and sand down with 120 grit. I then primer, then sand with 220.
BTW, if you are going for a gloss painted finish, then you will have to be sure it is perfect. It may look good in the filler or primer stage, but once you paint it all the imperfections will show up. A good way to prevent that is to feel the imperfections rather than try to see them. Just close your eyes and run your hand over the surface. You will be able to feel the high and low spots, and will know how much more you will have to sand.
Steven Kephart
Adire Audio
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i agree. but id suggest sanding with some even finer grit paper than just 220. basically, the finer the grit you sand with, the smoother its going to be. you could work all the way up to wetsanding with 2000grit if you want, but that isnt neccessary. just start with 60 and work your way up until you are satisfied.