Homebrew fairing compound

[galleywench]

Hey all, I'm about 1-2 weeks out from where I can actually begin fairing the decks of Magic and I have a few questions regarding mixing up my own fairing compound. I like the thought of the pre-mix products like Awlfair or Quickfair, but I still have quite a bit of regular epoxy left and want to save money where I can so I'll be making my own. I've done a bunch of thickened mixes in the course of the recore but none with the intent of fairing. For the chainplate and through deck fitting areas I thickened with only Aerosil. It works for intended purpose, but not fun to sand. For some of the 'pre-fairing' between 2nd and 3rd layers of epoxy I have been doing a 1:1 mix of Aerosil and Qcell glass bubbles. It sands better and the Qcells make a really creamy, easy to spread mixture. However, for the actual fairing compound for the final layer, I've read that some people are using ratios in the order of 2 or 3 parts Qcells/microballons to 1 part Aerosil/Cabosil. I'm sure it makes for much better sanding, but how does it affect durability? Also, with a higher ratio like that, do I need to do an epoxy overcoat to seal the Qcells/microballons or will a 2 part primer suffice?

I should note that I am doing a bunch of 'pre-fairing' before the 3rd layer is laminated in place so the amount of final fairing should be minimal (fill depth shouldn't be more than 1/8" max).

Any input would be greatly appreciated.

[Quetzalsailor]

Read up in West's information, too.

I don't think that there is much to fear in making fairing compounds; that's what you do with West System.

I will relate that the real issue for us amateurs is the way various mixes and sequential applications tend to have varying densities. Thus they sand differently and it will be difficult to achieve adequate perfection under painted surfaces. Rather like expecting to get a decent finish on ordinary fir plywood.

[galleywench]

Read up in West's information, too.
I don't think that there is much to fear in making fairing compounds; that's what you do with West System.

From what I've read I think your correct. My main concern is durability down the road. If I just put enough Aerosil in to get the thixotropic properties I need and add a bunch more QCell for sandability, will the cured compound come apart when the deck is walked on? Alternatively, is it overkill if I go with a mix that is heavily weighted on the Aerosil side do I just make more sanding work for myself without any benefit?

I will relate that the real issue for us amateurs is the way various mixes and sequential applications tend to have varying densities. Thus they sand differently and it will be difficult to achieve adequate perfection under painted surfaces. Rather like expecting to get a decent finish on ordinary fir plywood

From a consistency point of view I've been pretty lucky so far. I have a 5 gallon pail that I mix up a 1:1 mix of Aerosil and QCells to get the ratio roughly correct (and consistent across multiple epoxy batches). I've found a nice spreadable putty can be made when I add a one quart cup of mixed up fillers to 18 oz of mixed resin. Of course if you let the filler sit in the quart container before adding to the epoxy it compresses to about 2/3 of original volume, but this method seems to be working for me pretty well. For the actual fairing stage I hope I can up the QCell ratio in the 5 gallon pail.

I may just be overthinking things at this point. Or maybe I've spent a little too much time alone in my shed with big bottles of glue.