Multiple problems with fiberglassing hull -- advice?

Hmmm...I've just finished fiberglassing the hull and it didn't go well. I have multiple problems:

1) waves in fiberglass


2) rough edges at bow and stern fiberglass patches


3) white spots where I did try to sand and caught the fiberglass

I know I'm stuck with the last problem, but:

  • How do I avoid the white spots when I start sanding? Do you get them whenever you sand through to the fiberglass? (I've read several of the posts on this, but everyone seems to be able to avoid the fiberglass, but I'm not sure how)
  • How can I "feather" the epoxy on those patches so they flow into the epoxy around them? (here, I really can't see how I'll avoid the fiberglass when sanding the edges of these patches)
  • Any way of fixing or covering up those waves in the fiberglass (the worst problem)? Keep adding epoxy to fill in the waves and deal with the weight?

Thanks for any help,


9 replies:

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RE: Multiple problems with fiberglassing hull -- advice?

I can't comment on 1) and 3) but I don't see 2) as a problem.  Once you put on a few fill coats of epoxy and do some sanding, those edges where the fibreglass overlaps will simply disappear.


RE: Multiple problems with fiberglassing hull -- advice?

Thanks Dogan. When I start sanding the edge on (2), do I need to avoid hitting the fiberglass at all to avoid white spots? ...and therefore add quite a bit of epoxy at the edge before sanding?


RE: Multiple problems with fiberglassing hull -- advice?

I had a similar problem with corrugations on my Ganymede. It comes from not squeegeeing enough epoxy so the cloth floats up on it. The rough edges will feather out easily when you sand out the hull. The white spots will disappear when you apply the finish coat of epoxy. Don't be afraid to sand down to the cloth; just try not to sand through it. You will have to sand through it, though, to get rid of the corrugations. Fortunately, these tend to happen where the cloth is least needed. You can either apply another layer of cloth, or just cover it over with epoxy, which is what I did. Remember, it's the epoxy that makes it waterproof, not the cloth. The cloth gives it strength and impact resistance. Hope this helps - Wes

RE: Multiple problems with fiberglassing hull -- advice?

I think the corrugations (or waves) came from the previous step of smoothing the fiberglass out. I had a tough time getting the fiberglass to lay flat against the bow and had to "move" a lot of fiberglass down the sides of the boat. I think that put some twist or kinks in the fiberglass that weren't visible until I had the epoxy on and forced it around the hard chine. I saw the corrugations while the epoxy was still wet and did my best to smooth them out before it hardened. No matter how much I squeegeed (word?), the correugations remained.

As for removing them, I'll try your suggestion, Wes, and hope for the best. Sanding some and then try to cover with epoxy. Not really interested in sanding down to wood and adding another layer of cloth. My guess (with my skills at least) is that that would probably be more visible in the end.



RE: Multiple problems with fiberglassing hull -- advice?

I haven't mastered the art of posting photos on this site, but you can see photos of the corrugations on my Ganymede at
I just sanded them out until everything felt smooth, then added another coat of epoxy. The boat is now varnished and there is no sign whatsoever that they were ever there. -Wes

RE: Multiple problems with fiberglassing hull -- advice?

From the look of the picture (2), I would say 3 or 4 more coats of epoxy on that edge prior to any sanding would smoothen it out. 

I added a strip on the bow of my CH17LT just like that and I coated it many times before sanding (just around the strip, not the whole hull).

RE: Multiple problems with fiberglassing hull -- advice?


My first boat had the same problem as photo 1. I sanded the cloth smooth, almost down to the wood, and added a second layer of cloth. After a couple coats of epoxy and feathering the edges it all became smooth and invisible. Photo 2 is normal for bow and stern patches. They require a few coats of epoxy and you'll have to feather the edge of the cloth, meaning you'll be sanding into the cloth to make it blend. That's normal and nothing to fear. Photo 3, as has been pointed out, is no problem and will be taken care of with the next fill coat. Nicking the cloth occasionally isn't a bad thing, sanding thru it is. Even that can be fixed with a small patch of cloth that will become invisible with fill coats and feathering. Remember, you're building a boat, you'll learn how to fix one at the same time. That skill will probably come in to play in the future after a few years of use.

Have fun!

George K 

RE: Multiple problems with fiberglassing hull -- advice?

A flexible cabinet scraper is a great tool for feathering the edges of fiberglass tapes or patches, without abrading adjacent surfaces.  If you sharpen them frequently (with a file, and burnishing tool) they're very satisfying to use.


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