Hi windsurfer 18, 

the advantage of doing it the original way is to ensure you have the longest pieces and dont, in your sanding, take long runs and cut them into shorter runs....which degrades the strength a tiny bit. (btw i don't take credit for this analysis, but read it in a book discussing glassing technique and why the order is the way described and not reversed)

it can also be challenging to properly fill/wet out pieces that are going over shorter pieces becuase now there are little shelfs the bigger peice has to work over when it gets to the edge of the smaller piece. bending over those little shelves are also a negative for strength - to the extent possible, you want the straightest fibre runs possible.

finally, i am not sure you would find that you would save a lot of time in sanding.   the best way to save sanding time is careful, neat, glass work and some tricks like cutting pieces to clean lines when it is plasticy vs messy work that is allowed to fully cure.

all that said, i highly encourage folks to experiment and see if there is a better mousetrap.  but there is a lot of accumulated experience on this particular point that i think explains why it is the default approach.

h

Howard's right. The edge transitions have to be smooth or there is the chance of voids which would be the starting points for delamination or leaks, or blobs of epoxy which could float the cloth. You need to either feather the edges or fair them before applying glass that spans the transition and you have to do it for every layer where larger glass covers smaller. Whereas you can have multiple layers of smaller over larger and only need to fair once upon completion, so it's actually more work putting larger on smaller.

Laszlo