Saturday, April 23, 2011

Here's a bit on fairing

I faired the floats using the "candy bag method" ie put strips of fairing compound every 10cm or so, fair down to get the level, and then fill between the ridges.  I had to fill three times because the compound shrinks as it cures.  I used SP system S-Fair 600 which is a smooth, quite heavy and very expensive compound.  It's not very easily sanded and takes forever to cure.  Theory is that you'd rather spend time applying fairing compound than removing it.  In retrospect, this does not seem like the best way.  It might have been something about my fairing skills at the time, but the fact is I probably had to re apply fairing compound at low spots 20+ times before I got the desired surface finish.

From a link on Andrew's blog, I got acquainted with the air plane home builders' method of choice, and this is more or less what I have been doing now, also supported by the preferences of the pro that I had a few days, and who is back now to finish the hull.  Some problems though, as when I ask my worker (the not so pro one) to fill the low spots before he goes home, I return the next morning to find he has applied an insufficient layer of fairing compound to 3/4 of one hull side instead of filling the low spots (that I already pointed out to him) on both sides.  So had to fair almost all of it back instead of the patches before the big fill.  That's life when time has to be divided to several tasks and obligations.
I also changed to mixing up my own compound.  This seemed to me as an unpleasant task at first, but it's not that bad actually.  I use Svapox epoxy with GL hardener, an inexpensive laminating system with a medium working time, and add 27% weight (about 300% volume I'd guess) of micro glass balloons to get a non sagging, quite dry (have to use force and slow speed for it to attach properly) and light, easily sanded compound.  The point is to fill ENOUGH to fill all low spots, then sand back to the correct contouring in one go.  Preferably, the low spots should be pre filled and sanded when not fully cured (cheese grating) in order to avoid any low spots to occur due to crimp during cure.  I use my favourite grit 40 on the rigid board until I have the perfect shape and see the high spots of the laminate shining trough the filler.  This saves huge on time spent, and it is much easier to get an even surface compared to the patchwork on the floats.  Then it's time top fill pin holes, and change to finer grit to prepare for the water penetration barrier.
I guess all this is subjective, but this is my experience.

A few shots of the situation after removing 90% of yesterday's compound today:

These kind of disrupted surfaces takes a lot of time:

And I finally made the hole in the bobstay anchor, had been postponing it for a few years:

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