I’m new to boat building, and I didn’t see this question answered. I’m building the Jimmy Skiff II, and I plan to apply fiberglass tape to the fillet joints while they are still wet (instructions page 39) to avoid the sanding that the instructions say is needed if I let the fillets dry first. What I can’t tell from the instructions is the timing of when I am supposed to saturate the fiberglass tape with unthickened epoxy as shown on page 40. In other words, do I immediately apply the unthickened epoxy to the tape so that both the structural fillet and the saturated epoxy are curing at the same time? Or, do allow the structural fillet to cure with the fiberglass tape in place (installed while wet) and THEN once it has cured start the saturation process with unthickened epoxy? Sorry if this has been answered elsewhere…. I couldn’t find it.
I put the fillet in and clean it up and immediately put dry fiberglass tape on it. The tape will start to absorb some of the epoxy right away. Then I trim a chip brush down so the bristles are about a 1/4” long. I use it to coat the tape with unthickened epoxy. It’s kind of a gentle stabbing motion. The main thing is to soak the cloth and chase out bubbles. I also brush the epoxy past the edge of the tape onto the untaped surface a little, say 1\2 inch.
You must saturate the tape as soon as it is applied. If you were to simply press the tape onto a soft filet, then wait for that to set, then attempt to saturate the tape you’d end up with areas of tape at the boundary between the fibers stuck to the filet and those that remained dry that wouldn’t completely wet out. You can wait a few minutes for the filet to become slightly plastic instead of freshly-laid soft before applying the tape, that can help you prevent deforming the shape of the filet as you lay in the tape. Realistically, however, depending on the ambient temperature, how many linear feet you are taping (and the complexity of the filet shape), if you start laying tape as soon as you finish filet shaping, your filet will be well into the plastic stage by the time you get the last of the tape in - so just be careful not to deform the soft filets too much when you start taping. Same teqhnique as Jon just said.
My favorite method is to lay down the fillet, brush it with unthickened epoxy to smooth it, then pre-saturate the tape with epoxy (known in the professional composite industry as pre-impregnating or prepreg) and then lay down the tape while everything is still wet. Details & rationale:
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Brush the fillet with unthickened epoxy to smooth it - if for some reason I get delayed, having smooth fillets will keep me from having to do heavy-duty sanding. If the delay is less than 3 days, I won’t have to do any sanding at all. If it’s longer, then just a light sanding is all it will need. And unthickened epoxy instead of denatured alcohol or acetone avoids incompatibilities in case the alcohol or acetone is contaminated.
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The prepreg process - roll the tape up, put it into a jar, pour in the thoroughly mixed epoxy (resin & hardener). Squeeze the roll with gloved hands to make it absorb the epoxy and thoroughly saturate. Take the roll out of the jar, squeeze out the excess and unroll the tape onto the fillet. Run your gloved finger over the tape to press it onto the fillet and to squeegee the excess epoxy off the tape (I prefer a gloved finger because I can better judge the amount of necessary pressure, can directly feel any bumps or valleys and the roundness of a finger is less likely to dig in than a tool).
Doing it this way uses less epoxy, is potentially much faster than putting down the tape and then saturating it and completely avoids unsaturated or otherwise unsatisfactory tape (if there is something wrong with the tape saturation, I just put it back in the jar and try again; if that doesn’t work, discard the tape). I simply never put a substandard piece of tape into my boat.
The biggest caution is to squeeze and massage the tape gently. Too much handling will generate loose threads and glass “snot”.
Hope this helps,
Laszlo
Thank you for all these replies … EXACTLY what I needed! Much appreciated!
I absolutely agree with Laszlo’ prepreg recommendation, but one word of warning. I have used the cup technique multiple times and it works well, but in warm/hot conditions the epoxy will kick very rapidly. In hot weather, I wet out the tape on a table then use a plastic spreader to wipe off excess epoxy. When the tape is laying flat, it the epoxy is much slower to kick so I don’t roll it up until I am ready to put it into the boat.
Great tip… its very hot here and I’ve noticed the impact!
I had a whole cup of epoxy go off a couple of years go while I was holding it in my hand. It was a little frightening. I tossed it into the yard. The sooner you can get it spread where it needs to go the slower it will kick off.