Applying Fiberglass to 3/4" Rounded Edge?

[PeteCress]

viz: http://tinyurl.com/82weba9

The flats are already glassed and I'd like to cover the edges too - more to keep water from penetrating the el-cheapo 3/4" ply than anything else - but it seems like an interesting technique/test case.

I've got some 1 1/2" fiberglass tape.

With the right amount of brushing/coaxing I think the weave could accomodate the shape without having darts snipped into it.

But that leaves adhesion while the resin is still wet.

Is it even possible to do this?

If so, what would the trick(s) be for keeping the tape laying flat while the resin sets up?

I've got some wider tape - maybe 2 or 2.5"... but don't want to waste it if 1.5" can be coaxed into doing the job.

[woodpile]

Could probably wrap some peelply, aka, release fabrick around it and tape the peelply on the dry areas to hold it in place till the resin kicks. The peelply works good for stuff like this cause it helps blend in the cloth edges.

http://www.jamestowndistributors.com...e=GRID&history=

[JimD]

It'll be tricky no matter how you try it. Can't see any way the tape will take the shape without cutting darts. You might try just cutting thin strips of cloth - very carefully. Wet the ply edge with epoxy, lay the dry strip on - very carefully - and then wet out the cloth. Don't bother with brushes, just use well gloved fingers. Or you could just not bother. My usual approach to a situation like this is to work thickened epoxy into the end grain after its been wetted with straight epoxy.

[PeteCress]

http://www.jamestowndistributors.com...e=GRID&history=

That served to remind me that vacuum bagging is something worth learning. Reading The Board Lady's blog on professional surfboard/windsurfer repair (http://www.boardlady.com/repairmenu.htm) a few years back made me a believer, but I never fully confronted the problem of obtaining a vacuum pump.

I'm guessing that, although it would be totally cost-ineffective, vacuum bagging something like this would do the trick quite nicely: wet it, bag it, apply enough vacuum to cling but still allow maipulation, massage it through the bag until all the wrinkles are out, then turn up the vacuum all the way.

I think I'll wimp out on this one and go JimD's route with thickened resin.

[Gib Etheridge]

If you thicken the resin with chopped glass it will do pretty much the same thing. You can chop your own with a pair of scissors. The strands will have to be short, maybe 1/8".

[JimConlin]

I assume that you're talking about a 3/4" radius corner with some porous ply edge in the neighborhood, and that the corner is roughly a right angle.
Your 1-1/2" tape is not useful for this. The circumference of a 3/4" quarter-round is about 1-3/16". This doesn't leave enough tape for a meaningful lap on the panels. If you had 3" tape, I'd OK using that.
I'd suggest applying two strips of cloth, cut on the bias, about 3" wide. Be careful with bias cut cloth, as it's easy to pull it in length which makes it narrower and it's then hard to get back to consistent width. The bias cut is much easier on curves. Apply it dry, one layer at a time and then wet it out with a brush. Stagger the two strips laterally a bit so their edges re not in the same place. When fully wetted out and lying flat, apply some peelply (nylon taffeta coat lining is an OK substitute) and coax the whole works flat with bondo squeegees.

[chas]

If you were doing it again you might glass the curves first, by wetting out a long strip of 1-1/2' tape, cut pieces at 3-4" and half-lap your way around the curves. Sand and fair prior to glassing the faces. Now, I might just epoxy the endgrain and fair with a rich 407 mix. / Jim

[Todd Bradshaw]

With bias-cut strips, it's not difficult to wrap an edge as narrow as 1/4", but regular, fore and aft woven tape is much more difficult to work with. The neat edge of woven tape actually makes this even worse as it restricts the ability of the yarns to move on each other and conform to a non-flat shape. You may find that any time you're covering a complex shape with fiberglass, cutting off the selvedge edges may be well worth the trouble as it frees up the yarns. That doesn't, however, mean that the cloth is going to lie down neatly as you try to bend yarns over an edge. It can set up a scenario where your next hour or better involves running back and forth trying to stick down bubbles where it keeps lifting until the resin stiffens enough to hold them down. Not a good time or a formula for success at all.

Before I forget to mention it, seal the crap out of the plywood edges with unfilled epoxy resin (multiple coats) before taping the edge. Otherwise, it will suck the resin right out of your laminate. One other thing that you can try is to roll a light coat of resin on the area, let it cure until it is no longer liquid, but still sticky, lay your tape on the sticky stuff, lightly brush or coax-out any bubbles with a dry paintbrush and then go back and saturate the cloth with more resin and a brush. The tricky part of this is that the timing can be critical. You really don't want the initial coat partially saturating the cloth as it can harden there and leave dry spots that can't absorb more resin. It has to be hard enough not to penetrate the tape, yet you need to get the cloth stuck down before the sticky surface hardens enough to no longer be sticky. Whether or not this method is possible depends on the particular resin used, the temp/weather conditions, and also how large the taped area will be. Once the surface reaches the proper hardness and tacky state, it probably won't stay that way for very long. It's certainly not as easy as using bias strips, but if you time it right, it usually works. For a much more relaxed approach, cutting your own bias strips is the way to go. This is one tip of my old Prijon Leiser kayak paddle. It shipped with aluminum blade tip protectors, which quickly wore through. I eventually pulled the aluminum and covered each tip with three layers of 7.5 oz. fiberglass cloth, cut into bias strips. Even though the wooden blade is only about 1/4" thick at the edge, it was no problem getting the bias-cut cloth strips to wrap neatly around the entire end - front, back, sides and the edge itself, forming a cap over the end of the blade. With pre-made fiberglass tape, this simply would not be possible.

[the_gr8t_waldo]

3/4 rad is really hard to work with....it'll get considerably easyer if you can increase it to 1" or more. cut yer own tape so that it's on the bias(on a 45 degree angle as it passes over the chine). consider changing the layup to two layers of lighter tapes..the last bigger so that it's about 1" over the first........ and coat the raw wood with epoxy untill it'll not accept any more epoxy, befor rolling out, and wetting the tape. i've had some luck wrapping small dias, by covering the works with peel-ply and then a full 12"'width of saran-wrap. you can press out all the air and if the edge seal is good enough( always wanted to try masking tape for this), no air will be able to enter the matrix and allow the fiberglass tape to lif from the plywood.

[TXdoug]

There is good advice on this thread. Skip the tape and use some bias cut strips. I can't tell how big your part is but I have Vac bagged small parts with a seal a meal.


Another option would be to use peel ply then wrap and spring clamp some mattress foam over it to hold things tight.

[bwd]

ppsssssssssssst

3M 77
glass
resin
done

[Todd Bradshaw]

3M 77

Spray contact cement? Sounds like a perfect recipe for future delamination to me.

[JimConlin]

Todd,
3M #77 is widely used in laying up dry reinforcements before infusion.

[Todd Bradshaw]

Interesting. How do they handle the fact that you are then coating your primary bonding surface with a coat of something that isn't going to stick as well as the resin itself would? I could be wrong, but it kind of reminds me of the old paint bond thing, where a fresh coat of paint is only bonded as well as the old layer under it. Seems like a lot of trouble when all you need to do is cut bias strips and they'll bend over just about any radius using nothing but resin.