When I built my first boat back in the 80s my attempt to
fillet and glass in the bulkheads was woeful. I took a
piece of 4mm ply and shaped the end of it and then commenced
to try and coax the filleting compound into the joint.
Of course I ended up with a right mess.
I read how it is wise to tape either side of the fillet so you
can remove the tape and the mess prior to glassing.
The other problem that I had was the filleting compound would
squash out of shape.One could wait until cured but that would mean
sanding the fillet to get it smooth enough to take the glass tape
with no air gaps between the two.
These days a very simple and effective method has evolved.
If using 100mm tape I coat 50mm either side of the joint to be
filleted and glassed with resin mixed with slow hardener.
Then I make up the filleting compound with resin with fast hardener.
I deposit the filleting compound in blobs along the joint and run
a bit of rubber 4mm thick and 2.5 inches by 2.5inches with a rounded
corner. The round on the corner is the shape of the fillet that I want.
This rubber tool distributes the compound into the joint and cleans up
the work in the one operation. I then wet out the glass tape on a separate
board and use it to glass the joint.I also apply peel ply an inch or so wider
than the glass used. If doing a few joints by the time I get to glassing
the first one the filleting compound has gelled enough to hold its shape
but still soft enough to take the glass.
Below is a pick of a joint done this way.
The joint is very smooth if you run your hand along it and
very little effort required to fair the edge of the glass tape as the peel ply has done most of the fairing already .
It's a pity my photographic skills didn't also improve along the way.