fiberglass problem!

Hi all,

I'm building a Petrel kayak. I finished all the stripping. Sanded the deck, put on a first layer of glass, let it dry until tacky and then applied a fill coat of epoxy. I'm working in a barn. While I was working the temps were in low 70s. After I finished the glassing, the temp went down to mid 50s. Several weeks ater, the fiberglass started to delaminate in one place on the deck. In another place, it got a crack. I haven't yet glassed the inside.

I'm attaching pictures with links because for the life of me, I can't figure out how to embed pictures in this post.

What went wrong? Did I apply the glass too thick? Was the temperature wrong? Did I not sand enough or sand too much? How can I make sure this doesn't happen again? And how can I fix this? Is it best to sand off this section and apply a fiberglass patch?? I'm so bummed!

Thanks in advance,


9 replies:

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RE: fiberglass problem!

   Pics didn't show... But without looking my first two suspects would be a poor mechanical bond.  Sanding is normally the culprit.

Other advice is to use a digital scale in grams when mixing epoxy.  You'll have way less chance of a random uncured patch occuring....which will cause a delamination issue.

RE: fiberglass problem!

   Saw the pics.  Any chance oil or something got on the surface between coats?  

RE: fiberglass problem!


It’s frustrating but don’t let this get you down. At all.  After you use the boat for a few seasons you’ll end up fixing something like this anyway. Now you’ll know how.
I’d guess you didn’t squeegee out enough epoxy on the first bedding coat. You want to stop squeegeeing one stroke before it’s too dry ;-) . No way to tell for sure from here though.
Without seeing it I’d guess finishing the fill coats before fixing the bubble would be a good idea. That way you’ll have a solid thickness of epoxy to work with when sanding and feathering the patch area. You want to have enough epoxy that you don’t cut into the existing glass when feathering edges. Use your best judgement here.
Sanding the bubble off isn’t a good idea. Use a utility knife to cut away the offending section. Try not to score the wood, it’l telegraph. If the patch will cover your beautiful pattern work consider pealing the glass back to a less visible spot. Parts of patch will likely telegraph through. To do that you’ll probably need a heat gun to warm the epoxy enough to release. You’ll want to be very careful not to overheat. And the fumes released are very very unhealthy, use a respirator outdoors. Seriously, you can feel your brain cells dying.
Next thing is to feather the old glass edge. You could sand the edges but run the risk of cutting more wood than glass/epoxy. Since the wood is so much softer than epoxy you can cut through a lot of wood before the epoxy is feathered enough. A curved carbide paint scraper would be great here. The curved edge will let you focus material removal accurately and the carbide keeps an edge practically forever. Your nearest big box/hardware/paint store will have them in several sizes. Work towards a transition where you can’t feel the edge. It sounds like using a bazooka on a fly but trust me!
Wipe with denatured alcohol after a good sanding to make sure any (possible) contamination is removed.
Cut a glass patch two inches or so larger than repair area. I make them a little larger still and remove some of the threads of warp or weft leaving a fringe of one or the other depending on orientation. The remaining threads will be easier to feather into the existing epoxy. Again, curved carbide paint scraper is a good choice.
Sticking the patch down will be a sloppy pain, glass will want to shed from the patch. Pick the blobs out as best as you can. I’ve had good luck putting the patch on then covering with cling wrap and squeegeeing the patch through the wrap. Cuts down on gobs of thread pulling free. Get the patch well bedded, you don’t want it floating in epoxy. Leave the plastic wrap on till the epoxy kicks so you don't pull the patch up. Fill the weave only after it’s good and kicked, you don’t want to take a chance on pulling the patch loose on the fill coat.   

My guess would be the glass pulled free during the extended cure time at 50 degrees, or you tugged one corner when the epoxy hadn’t kicked yet and stressed the cloth enough to pop loose when you weren’t looking. You’ll be able to get a read on it by examining the area under the pulled away section. If the epoxy looks (feels) well adhered to the wood you had a mechanical problem like the glass wasn’t bedded thoroughly or gravity sucked the glass free. I don’t think you had an epoxy ratio problem as the rest of it cured properly. It’s possible there was an unmixed pocket in your batch. Stir the daylights out of it then stir a little more. Epoxy is a chemical reaction process and all the material has to be well incorporated to cure properly.

I’m mystified by the crack.

Let us know what you find when you get in there.


RE: fiberglass problem!

   Always use a digital scale in grams when mixing epoxy, it's way better than the pumps. From what I read about your lay-up, it seems to me you let the epoxy tack-up and then you applyed more epoxy on curying epoxy? Bad move, you fish-eyed the epoxy. This should have never been done, let the epoxy cure before you add more. And any bubbles you people have in your lay-up's, Use Peel-ply and you'll never have bubbles again.

RE: fiberglass problem!


FWIW, I never use scales, just pumps, and I've frequently put more epoxy over epoxy that had not finished curing. Nor do I get bubbles even though I never use Peel-Ply.

All that to say (without starting any religious wars about the merits of the techniques), that I respectfully disagree with your diagnoses. I think Karmi had something else going on that needs to be solved before moving onto new mixing and layup methods.



RE: fiberglass problem!

   I looked at the photos.  Nice woodwork under there!  I'm with Silver Salt on how it happened. The glass pulled under gravity or a bit of tension from elsewhere and caused it to lift up, my best guess.  The low temps meant there was more time to let it happen when you turned your back.  If it was surface contamination, I'd expect more random or general bubbles.  Those have the elongated look of a wrinkle or pucker.  I had a couple of these happen on my skerry.  I used my Dremel tool with tapered and round cutting bits to nibble away the lifted glass. I wasn't sure I could cut them with a razor without slicing myself or the boat. Then you can patch like SS described.  I just filled one or two with thickened epoxy mix because I was painting, they weren't in critical spots and wanted to get on with it.  The one that looks whitish may be a spot that just didn't quite get enough resin on the first coat.

Also, like SS says, squeegee the heck out of the fabric, but smoothly, so as not to drag it.  I've used peel ply, but it really is best on flat surfaces.  On compound curves, even gentle ones, it doesn't like to conform as well as the glass.

I agree with Laszlo that it doesn't look like bad ratios, and I never had any trouble using either pumps or graduated beakers with the Mas epoxies.  Other systems which have big ratios like 4:1 or 5:1 might get more finicky but not Mas.

RE: fiberglass problem!

thanks for the pictures.

my question that i think really determines the way you go here is, what is the quality of the epoxy/glass adjacent to the bubbles....and is it properly cured?.

if you take a dull nail and push it into the epoxy adjacent to the it dentable/rubbery or is it hard and solid (for that matter you can test the entire surface that you recently glassd)

if it is hard and solid....then you epoxy was fine and something caused the cloth to ripple up before it cured it happened is not particularly important.  if that is the case...properly cured epoxy....then you can just cut the bubbles out (and any remaining loose glass) and apply epoxy and glass over it and feather it in....just like a normal glass repair if you had a scratch that went through the glass.    

if its not properly cured....e.g., rubbery....then you need to address that prior to moving forward.  good epoxy over improperly cured epoxy will never resolve that problem.

do the nail test around each bubble and the overall surface....sometimes, with multiple batches in a session, one of the batches can be messed up if you got the mix wrong and the and so you have problems in only one area.

before we get into how you resolve that, let us know what's the basic answer on the epoxy quality that has been applied.


RE: fiberglass problem!

   Thank you all so much for the insight! I really appreciate the tips about how to make the patch and fix this going forward. 

  After some reflecting, I think that the cause of the problem was that I didn't mix the epoxy well enough. I believe this is the case because the section that is bubbled is flexible. If the epoxy was properly mixed, it would be hard. Lesson learned. I'll certainly make sure that it doesn't happen again!

RE: fiberglass problem!

   Actually a layer of fiberglass wetted out with resin and cured will remain somewhat flexible.  If it is sticky to the touch or has slime that wipes off (uncured resin) then you had a mixing problem.  If it is dry, but flexible with a hollow underneath it, you mixed ok, but it just pulled away from the surface some way.  Either way, definitely fixable.

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