How sharp to make tail edges before laminating?

Hi all,

I’ve been trolling through the archives and learning a ton before I shape my first board. There is one question I can’t find the question to. From my experience with fiberglass as a boatbuilder years ago, glass doesn’t like to wrap around sharp corners without creating an air pocket. I imagine that the foam needs to be rounded a bit in the tail section and then the sharp edge reformed with a resin dam on the hotcoat. My question is how round do I need to make this edge without creating too much work for myself. I’ll be starting two boards, a mini-simmons and a classic fish. Wrapping the tail of the fish actually is giving me a bit of a mental challenge as to the best way to go about it as far as the buttcrack and pin tips.

any suggestions are greatly appreciated



Shape it the way you want it.  Hard edges can be glassed even by a first timer, if you babysit them.  Get the cloth saturated well and squeeged down.  Once you got everything else, flats, nose and tail relief cuts, rails lapped, excess resin pulled off and resin removed from the opposite side, then come back and using your finger or a hard squeege press that edge down again and squeeze any air bubbles out.  Be patient and wait it out.   I use my finger to press that edge down.  I press hard and run my finger along the edge towards the tail.  Sometimes you will have to do this a few times before it sets.  Another good reason to use UV.   Once you get where you want it, just walk outside and it will stay.  Certain brands of cloth are more prone to bubbles on hard edges.  Saturation and flexibility of the cloth is important.   I recently started using BGF Aerialite for that very reason.  Got tired of chasing bubbles and strings with Hexcel.   Use a resin dam on the hot coat.  I shape mine fairly hard and then get them really hard on the hotcoat.

Thank you sir!

I’ve seen the images of finished shapes before the glass and noticed that the back edges were sharp on most boards and wondered how the lighter glass like 4/6 oz did around those corners. Most of my fiberglass experience is with 12-18 oz and woven roving that definitely didn’t like sharp edges. 

For the buttcrack on a fish, do you just wedge a small piece to fit in there to cover the gap that would be left by the relief cut?


Appreciate it!

The foam after shaping does not need to be razor sharp.  If you soften the edge just a hair you’ll get a stronger tail.   Makes it easier for the glass to wrap the corner.  You then make the edge sharp in the hot-coat stage.

Thanks Mako,

I fugured I’d do a test with a scrap of foam just for my knowledge and soften the edges just a touch. Good to hear your experience. 


I cut a little triangle shaped piece of cloth and stick it in the crack at the last minute.  I use my finger to wet it and make it lay down.

Thanks McDing, Glad to hear a confirmation on my thinking from the experts. 

I don’t even try to wrap my little triangle patch.  I usually don’t need it when I do the bottom.  But when I do the deck there is usually a little area in the but crack on the deck that is sometimes exsposed foam.  That’s where I put my little triangle.  While my deck is still wet I stick the  patch in the crack with a single point pointed down.  I move it down until it covers the exsposed foam.  Wet it out with my finger and just let the single point hang straight down.  Later I either razor cut the point or grind it after the lamination has set.  I guess you could stick it on the foam before you wrap the tail.  But I am always afraid that my squeege work will move that little triangle out of position.  I’m also always hoping that I did such a good job on my relief cuts that I won’t need it.  The deeper the “butt crack” the more likely I will need it.  It’s also a little protection when sanding the crack.  A little extra buffer to protect against burning thru to foam.  Makes a cleaner crack too.  Smoother finish.

It’ll help to wrap the rail around a hard edge nice and tight, so the glass doesn’t have any slack to un-bend off the hard edge and bubble.  This should be obvious, but not all who may read this might realize it.

Interesting thread. I had no problem wrapping sharp edges with epoxy, until I started using s glass. That stuff just doesn’t do it the same. Seems logical to use the resin to build th sharp edge and get a better bond on the lam

Thanks guys! Really helpful info. I have 6 and 4 oz. warp glass and will probably easy the edge just a hair to help it out and sharpen it up with hotcoating. Will also do a quick test piece with a cutoff. 

Definitely right about S cloth.  A little more work to saturate and wrap.  E and Warp are easy compared to S.  Just babysit it until it sets.   Finger it.

I personally think Warp is the easiest to wrap.   Just my personal opinion.  I prefer BGF Aerialite.  JPS has a reputation of being easy to work with.  I haven’t used it in so long, that I couldn’t say.  I find Hexcel to be stringy and doesn’t saturate as easy.  On the hard edges it always seemed to leave a series of very small bubbles in the tail area of the rail.  To prevent this I took up the “finger” technique, which I have seen used many times by pros.

Good to hear McDing. I’ve seen that techinque used in some of the videos I’ve watched. If it gives me any trouble I’ll make sure and give it the finger! :wink:

since i use mostly 9oz biaxial stitch glass i have to round shape my edge for laminate and rebuild it with resin after… Aerialite is easy and fast to soak with resin,probably thanks to specific sizing, but i found that it show more “white wave” when boards dinged.

I tried masking tape (3M the blue one) and it worked!

Saturate the glass with resin, and lay it around the rails, until the surface below is wetted too, or wet the surface separately.

Let it rest until the resin starts kicking (Its about the time, the guys above used the thumb press or finger press method…)

If it kicked, but it is still tacky, use masking tape and tape the glass around the rail using the necessary pressure, to get no bubbles; mask directly on the tacky glass, no need for shrink wrap of similar separators. 

Wait until completely hardened. You then can remove the masking tape, sometimes it needs to scratched off with a scraper or a chisel, but finally it worked without major problems.