I forgot how much I hate this phase.
I'm sure there is a better way to do this, but I use bondo filler to create an even seem around the box. One step I should have done was to sand down the mdf before I started bond. In many cases, with the tight fit of the flat packs, I could have created a pretty even seem with sanding the mdf, with minimal bondo. But I didn't realize that until later.
Experienced finishers please weigh in, but from my noob adventures in my first build, I found that bondo works better than wood filler. Mainly it seems to lay down better and has less pits and holes in it. I'm sure I did something wrong, but I found with plain wood filler, as I sanded down the filler, I got pits/holes in the final layer and had to lay another layer. I got some of that with bondo, but much less.
As far as bondo, yes, this is the stuff used on cars. From what I read it works great with MDF. A word of warning is to play around with how much hardener to use and use smaller amounts of filler. If you use the "recommended" amount, it will dry very fast. If you are good with this stuff, that's fine. You can sand it in 30 min. But, if you are noob like me, that gets tough to get the filler spread out right, so I dialed back the hardener a bit. Takes longer to dry, but it easier to work with.
Once the bondo drys, use a rough grit to knock down the first layers and then when you are down to level (can't feel the filler edge) shift to finer grit. At least for me, even with a half sheet orbital sander, it takes me a long time to sand it down. And it takes a couple of times (filler/sanding) to get it right.BondoBondo Phase
. This is the second round of filler. You can see I already sanded down one layer and laid the next layer down.Post Sanding. This is the bottom of the box. This one is pretty smooth.Minor Fix. This is the other bottom that has a small pit that needs to be filled.Edited by Java - 11/22/12 at 12:44pm