Sanding fiberglassed hull & bubbles


 Two questions for the group:

1) I think I did a fairly messy job fiberglassing and applying epoxy to the hull and sanded today, first with 80, then with 220. After several hours of sanding, though, the surface is still somewhat bumpy...traces of drip marks and fiberglass strands are all visible. The hull is smooth enough for me to rub my hand over without any problem, but I just want to check to see if I should sand it until it's completely smooth (which seems like it may take many more hours). I've already applied three layers of epoxy; should I apply a fourth to smooth things out, or would that only make things worse?

2) I was sanding the hull outside largely in the shade this morning but sunlight was striking one part of the boat. There are now some air bubbles under the fiberglass in the spot where the sun was hitting the boat. Any thoughts on this?

 Thanks for any advice.


7 replies:

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RE: Sanding fiberglassed hull & bubbles

You've done 3 coats and you see strands of fiberglass  and the hull is somehat bumpy. NOT a problem. You can put as many coats of epoxy you want on until your happy. Also, if you wait no more then 24 hours between coats, you do not need to sand at all although you can sand if it makes you feel better. I found it's almost impossible to get a perfect smooth surface so don't worry about a bump in the road as you go. On your last coat after it dries, do a good job of sanding and try to remove what you can w/o taking off too much of the fiberlass. If you do, Add another coat of epoxy, again, not a problem

RE: Sanding fiberglassed hull & bubbles

#2 The bubbles under your fresh 'glass job were due to the wood "out-gassing" as it heated up in the sun.

 It's always a good idea to glass & epoxy when there will not be a significant increase in temp while it cures. It's a great idea to do it in the evening & let it cure overnight.

#1 Are you using a roller & tipping out after? You may need a 4th coat if you have sanded into the glass trying to fix drips and runs in the first 3.

However if your 4th coat has drips and runs, you will have the same problem & you will be back to sanding.


RE: Sanding fiberglassed hull & bubbles

Thanks to you both.

RangerAJ: Good analysis of what happened with the out-gassing. Any thoughts on what I can do about the bubbles underneath the fiberglass?

RE: Sanding fiberglassed hull & bubbles

I suppose if they are big enough, they could be filled with epoxy by using a syringe with a needle.

There are a few posts here that refer to how to do it.

Good luck

RE: Sanding fiberglassed hull & bubbles

ARanger makes a good point on apply the epoxy. You can do a really nice job when you apply with a foam roller and them "tip out" with a paint brush. After you apply the epoxy with the roller take a brush and lightly go over the entire surface in long smooth strokes.  The evens out the finish and can take care of drips if you missed any. Try doing this process methodically like doing the bottom panel then the side panel and then do the other side the same way. Good luck!

RE: Sanding fiberglassed hull & bubbles

Anyone know if it is possible to get rid of those tiny bubbles by sanding until you reach the fiberglass gloth?


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