Dealing with cut end of fiberglass

I'm getting reading to do the fiberglass on the hull of my WD12 and I'm concerned about the cut ends of the fiberglass un-ravelling when I brush epoxy on them - especially in the area of the bow and stern.

I had this problem when I glassed the inside of the boat - ending up with a balled mess at the cut end of the tapes.  Any suggestions?

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RE: Dealing with cut end of fiberglass

Hi DMK, 

that sounds pretty frustrating.   and yes, if you try to wet out cut ends of glass, and you get a little agressive, you are typically going to get a mess.

so the general approach to avoiding that is organize your glassing so that you are never really wetting all the way out to a cut edge.

on the outside of the hull, for example, the cloth is typically draped over the hull and the cut edges are hanging several inches below the hull and are not wet out.  when the epoxy/cloth starts to cure and gets to a plasticy state, it is cut away with a box cutter along to leave a very nice clean edge.

on inside work you can lay out a blue tape line where you want the glass to be and lay a bigger piece over it and wet out to the blue tape....then cut the excess glass with a box cutter to your blue tape and pull off the excess glass with the cut edge.   again, here in this technique, you never actually try to wet out a cut edge.  the picture below shows this technique.  you can see the cut edge is outside the blue line.  when it was plasticy, we just took a box cutter to the inside of the blue line and pulled the excess material off....nice and clean.

another example of using blue tape to avoid a cut edge is glassing the shown in this picture.  

again, when the glass has cured a bit and is plasticy, a box cutter is used to remove the excess   which then looks like this and is pretty easy to sand and fare in:

anyway,  i  hope you get the general idea...

all that said, to the extent you can't avoid it, it is important to be delicate wetting out cut edges and avoid trying to stroke it too much which will just lead to stands coming off.  easier said than done, i know,  but after a couple boats you would clearly get the hang of it.  but in summary, we just try to avoid that situation as much as possible in the first place...and if you can't you will just do some extra sanding



RE: Dealing with cut end of fiberglass

Usually I just outline the glass piece with blue tape before I cut it out. When it's cut, all the glass fibers are immobilized on both sides of the cut line. For really tight spots or where I want extra control, I do what Howard says and put tape on the boat, but I use clear plastic packing tape since epoxy can eventually soak through blue tape and bond it to the boat.


RE: Dealing with cut end of fiberglass

This is one of those things that I wish had a full page dedicated to it in the instructions, or perhaps some reference videos. The challenge of taming those cut edges surprised me a bit, notably when working with the multiple staggered layers (3 in some places) of cloth on the hull of a Shearwater sport.

However, speaking from the perspective of a total novice here, I can say that with some practice things got better. I eventually found how to get just the right brush angle, brush pressure, brush speed and quantity of epoxy on the brush to wet out those edged with minimal loose fibers. On any next builds though, I'm most definitely going to embrace that tape trick!

This leads me to a related question. For those of us who had trouble taming those edges when applying epoxy what sort of techniques should be used to properly blend-away the loose fibers while later sanding and filling the weave? I have numerous places where rouge fibers "flow" away from the cut line at an agle and are now forever embedded into surrounding epoxy. They are nice and flat, but as they are single fibers they create a pretty pronounced edge that I don't think will easily sand-down or cover-over. I'm not too worried about this, but I'm curious if there are any tricks to help blend these anomalies into a nice smooth surface. Is it as simple as just spending a little extra sanding time in these areas?

RE: Dealing with cut end of fiberglass

   I totally understand your frustration.  Even using the tape method, which works great, I inevitably have an area with a stray strand somewhere on the boat at some point in the build. What works for me is to use a sharp scraper to remove the stray strand, followed by a light sanding. This usually does the trick. 

RE: Dealing with cut end of fiberglass

Thanks Peter. Do you reccomend doing that scraping before adding the additional fill coats or after? It's not totally clear to me what level of scraping/sanding is best before filling the weave. I assume that large drips and runs (and maybe the lines form loose fibers) are best addressed before new coats, but I'm also wary about cutting into the fiberglass while it's still so close to the surface.  

RE: Dealing with cut end of fiberglass

   I usually do it as soon as possible, in order to give the subsequent layers of epoxy an opportunity to level out. If you wait, you have to scrape down through the new epoxy to get at the strand, which is a lot more work and will leave a dished out area that will then have to be filled in some way, especially if you're going to be painting the boat. Paint is much less forgiving of surface defects than varnish. Remember to use a light touch with the scraper and stop before you go too deep.  And doing this before the epoxy goes totally hard, usually within 2 days or so, will also make the job much easier. 

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