oops...hit sent before typing.

i tend to build relatively light so the key determinant for me on fillet size is no bigger than i need to/than is required to creat a shape that the glass that is going to go over it will conform to.

i find for me the large craft popsicle sticks which are approximately 6 inches by 3/4 inch is my 'go-to' filleting stick for nice neat small fillets that will pass the test above.  https://www.walmart.com/ip/Creativity-Street-Wooden-Craft-Sticks-6-Jumbo-Natural-500-Pkg/15039832?athcpid=15039832&athpgid=athenaItemPage&athcgid=null&athznid=tic&athieid=v0&athstid=CS020&athguid=fde34e93-1cf-171f661aa2c5be&athancid=null&athena=true

now these sticks will typically not be wide enough to handle the pointy end of a stitch and glue bow and stern as you can't get your fingers in to work the glass.  but for all the other filleting..this is what i work with.  

on your second question, yes, you can add over a fillet that is too small with no problem.

also as a note, i use painters tape laid down before filleting to help keep fillet need and material where you want it.  you put the tape down on either side of where you expect thte fillet to be.  after the filleting, you pull the painters tape up and you get a real clean line...and it looks very professional

h

   Hey ---  thanks for that quick reply. I hadn't even left the forum yet! 

Yes, I use the painter's tape method as well, but for some reason, my fillets this time came in well-inside the tape boundaries. Most of these fillets will be permanently buried inside the hull and so aethetics are less of a concern. But in the cockpit area, the fillets right now are maybe 1/4" wide. I think I'll be ok because of taping over them, and the hull is 'glassed on the outside as well. But I want to be sure so as to not compromise integrity, y'know?

Fillets are there only to support the glass tape. All the real strength comes from the glass. As long as the fillet is wide enough to keep the glass from exceeding its minimum bend radius, it doesn't need to be any wider. In the picture above the fillet is well under 1/4" wide and that boat is still going strong after 12 years.

The 3/4" wide craft sticks that Howard mentions are sized just right for 4 oz cloth. I trimmed a plastic putty  knife to the same radius as a US nickel which works well for 6 oz. cloth. It's also re-usable, the epoxy pops off once it cures.

As long as the glass tape isn't folded or bubbled up, the fillet doesn't need to be any thicker for joint strength. If you need to thicken it for cosmetic reasons, I'd recommend using epoxy/microballoon mix instead of epoxy/woodflour for the cosmetic coat. It's much easier to sand. Just put it on top of the glass., not under.

Laszlo

i know the concern. 

as i mentioned, if the glass will work with it, i think you are fine.  based on some of my boats, 1/4 inch does not sound that far off.  for example, if i am using a 3/4 popsicle stick on a right angle fillet....the fillet size would only be  ~ 1/2 of 3/4 ....which is a little over a 1/4 inch.  i just looked at some of my craft and the fillets are not disimilar to what you describe.  

i tend to think of skulls as boats that are not being 'hardened' to attack rock gardens or otherwise to smash around.   

there are some folks who legitimately are trying to create an 'expedition' grade kayak for extended trips in away places.....and they will use significantly more fibreglass and bigger fillets to withstand expected landings on beaches or rocks in sea conditions that are less than friendly....but you pay a heck of a weight penalty for that. 

for me, who stays in relatively kind conditions, throwing my back-out lifting a heavy kayak is my top concern...not breakinging an unhardened boat...so i keep it light and try not to bang it into anything.

h