fiberglass strips on exterior keel have air under them

Fiberglassing over plywood and one-off fiberglass methods. See: "Boatbuilding Methods", in the left-hand column of the Home page.

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Rob&Nick
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Joined: Thu Sep 14, 2017 1:04 pm

fiberglass strips on exterior keel have air under them

Postby Rob&Nick » Thu Sep 14, 2017 1:47 pm

Hi, All,

We're new here as posters, but have been reading the forum extensively for several months. Thank you for all of the help! We are building the 16' cabin skiff. We've finished the hull, frame and decks, and have now turned it over in order to work on the hull exterior. We're writing because our second application of fiberglass strips to the bow section of the keel did not come out properly. Our question is, how should we fix it?

We found a few posts here by folks who mention the same problem. One sanded off the white spots and applied patches. The other sanded off the entire fiberglass application.

We feel that it is particularly important that the fiberglass on the bow keel be very good.

Details (photos attached): This happened only for the second application of the strips--that is, for the wider strips that straddle the narrower strips underneath. The problem is that there is air under the fiberglass in several spots--one larger spot and a number of smaller ones. In those spots the fiberglass is flexible even though it has cured. Instead of being transparent, it is white. We know it should not be like that, and this is the first time this has happened. This is the first time that we left the boat outside where the air is cooler (about 50 degrees F).

Thank you--

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PeterG
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Joined: Mon Dec 03, 2007 7:08 am
Location: Connecticut

Re: fiberglass strips on exterior keel have air under them

Postby PeterG » Fri Sep 15, 2017 7:23 am

That is some really rugged, heavy duty fiberglass you have there. That looks like 17 or 18 oz. biaxial? That looks way too heavy for use on the exterior of a hull. I've used it for structural repairs in boats. I am not familiar with the design you are working on, but is that what's called for in the plans/instructions? Typically the Glen L hull designs recommend a light weight cloth, like 4 to 7 oz. for the exterior. The stitch and glue designs will use other types of fiberglass for reinforcement, applied inside and out but I'm not up to speed on those.

I can tell you what happened is the glass you applied was starved for resin. Not enough was applied to fill the weave. Or the resin drained out, ran down vertical surfaces before it gelled. Either way, I don't think you have any choice but remove the fiberglass, smooth out the wood, and start over. But first check that you are using the right type of fiberglass. Lay the fiberglass on the wood dry, no resin. Smooth it into place with a stiff, dry paint brush to make sure it's in contact with the wood. If it won't lay flat at corners because the fiberglass is too stiff, or has low spots that the cloth won't lay into, try reworking the wood surface to round the corners or apply some fairing compound made of resin mixed with a thickening filler at inside corners or low spots. Or switch to a more flexible weave of fiberglass. Apply the resin to the fill the weave, use a grooved roller to smooth out the fiberglass and make sure it is tight to the wood. This will also help push any excess resin around too. The fiberglass should go pretty much clear when it's wetted out properly. Any whitish spots under the glass are air pockets and should be rolled out. Let the resin turn to a gel state and apply another coat to fill the coarse weave. You can use a plastic spreader to push that resin around to a consistent thickness. Let it gel and then repeat the whole process for the next layer.

I hope this helps and that your boat comes out the way you want. Feel free to ask questions and most of all, have fun! Oh, and post pictures of you project, we all like to follow projects and it'll help others too.
Last edited by PeterG on Fri Sep 15, 2017 11:31 am, edited 1 time in total.
Murphy's Law: Anything that can go wrong, will go wrong.
Griffin's Law: Murphy was an optimist.

JimmY
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Location: Brighton, MI

Re: fiberglass strips on exterior keel have air under them

Postby JimmY » Fri Sep 15, 2017 9:34 am

Hi Rob & Nick,

I agree with Peter in that the fiberglass was starved for epoxy or pulled away from the boat. It might have been, being the second layer, that epoxy moved more if the glass below was smoother than raw wood.

With epoxy, it is not like paint where is will stay in place once you put it down. Epoxy will behave like a liquid until it gels and cures. Think of syrup that gets thicker and thicker over time, even though it is getting thicker it will still try to run and move. My guess is that the glass you are using is pretty stiff and if you laid it around the corner of your boat that it would not conform to it. So, when you applied epoxy you were able to get it wetted out and it conformed to the boat. You then went away and the glass was always trying to flatten out and pulled away from the boat before the epoxy cured. You will either need to baby sit the glass (keep trying to brush it down) until the epoxy gels, find thinner glass that will lay down, or find some other way to hold the glass and epoxy in place while it cures. If you are committed to using that glass, you might try peel-ply, which is just 100% polyester fabric, to hold it in place. You would wet out the glass, and then tape the peel-ply over it. The peel-ply will wet out as well, and you can add more epoxy to dry spots through the peel-ply. Just make sure to leave an over hang that is not over epoxy so you can rip the peel-ply off after the epoxy cures.

Whatever you do, I think you ill need to sand off the failed layer and try again.
-Jim
Nothing says poor craftsmanship like wrinkles in your duct tape!

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billy c
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Re: fiberglass strips on exterior keel have air under them

Postby billy c » Fri Sep 15, 2017 12:06 pm

Peter and Jimmy gives great advice above. I've used pretty thick tape on some of my fiberglass boat repairs and wetted the glass tape till it went clear before applying it to the hull.
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Rob&Nick
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Re: fiberglass strips on exterior keel have air under them

Postby Rob&Nick » Fri Sep 15, 2017 5:59 pm

Hi All,

Thanks for your replies. We have ground off the existing fiberglass and replaced it with thoroughly wetted out strips.
The fiberglass we're using is a quite heavy weave but is what was recommended for the seams. A lighter 7oz fabric will be used for covering the entire hull.
We'll post pictures of the boat when we get a chance.

Thanks again.

PeterG
Posts: 351
Joined: Mon Dec 03, 2007 7:08 am
Location: Connecticut

Re: fiberglass strips on exterior keel have air under them

Postby PeterG » Fri Sep 15, 2017 8:01 pm

Okay, sounds great! Glad we could be of help. Good luck and keep us posted!
Murphy's Law: Anything that can go wrong, will go wrong.
Griffin's Law: Murphy was an optimist.


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