Originally Posted by
sybrmike
A fillet is just a rounded corner. You can make bedding and fillet material by mixing a filler (micro balloons, talc, chopped strand, wood dust, etc) with resin to form a goopy putty like substance.
You want to use a bedding material between the stringers and hull so that there is uniform contact between the two surfaces which avoids air pockets and local stress points that can lead to cracks. It takes a little practice to get the consistency just right - too dry & it won't squish well, too wet & it won't hold shape. Be fairly liberal with laying down the bedding material and use what squishes out when you set the stringer in to form a radius (fillet) between the hull and stringer before it sets up (I like to use the rounded end of a 1" wide wooden tongue depressor). You'll probably have to go back after it sets to build up and dress up the fillets before glassing. Again, a fillet is just a radiused filler to help the glass lay down in the corner.
1-1/2" seems pretty big for biaxial cloth. I'm no glassman, but I can lay heavy 17 oz biaxial with a 1/2 to 1" fillet. Also, rather than sanding the fillets perfectly smooth prior to glassing - you can rough sand (80 grit) them relatively smooth & then lay down another pass of fillet filler material and then lay the glass while the filler is still wet. This way you can really work the glass into the fillet without bubbles. Preparation is key (cloth pre-cut, all supplies handy, etc.) & have to pre-wet the cloth, work quickly, & watch your resin kick times.