Sanded through fiberglass

I tried searching but couldn't find a post about this. I'm doing my pre-varnish sanding and while trying to smooth out around a low spot on the side panel of my mill creek I sanded a 1inch round spot down to wood. What is the best way to handle this?  I assume the integrity won't be affected and I'm goncerned that if I try to patch a piece of fiberglass over the wood it will be hard to hide. So should I just coat with 3 coats of epoxy in the spot or patch repair with fiberglass?

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RE: Sanded through fiberglass


If you just epoxy it, you'll need enough coats to match the height of the filled weave.

A 2" to 3" diameter glass patch will work fine, too. It's not that hard to hide it. It's just a matter of feathering the edges with some carfeul sanding.

Whichever way you're happiest to tackle it will be fine.

Have fun,



RE: Sanded through fiberglass

Good point. I just checked and there is a definite difference in feel between the two areas so I think I will try patching it thanks for the quick response. 


RE: Sanded through fiberglass

Scott, I'm assuming the reason you sanded through the fiberglass was because it was higher than the nearby surfaces, and you were trying to fair the hull before varnishing. It would have been better to build up the low sports before sanding, rather than grinding down through the fiberglass in the high spots.

A fairing compound made of epoxy thickened with easily sanded micro-balloons (or equivalent) can be used on low spots that will be painted. But since you want a bright finish, you might have built them up with extra coats of unthickened epoxy, or even an extra layer of fiberglass just in those areas, if necessary.

For your present situation, I see two options:

1) Apply a fiberglass patch (with fill coats) to the area that you sanded through. Also build up the nearby low areas with epoxy, and extra fiberglass, if necessary. Then sand the entire area fair.

2) Don't do a fiberglass patch, but apply at least 3 coats of unthickened epoxy to the entire area, including the low spots. Sand everything fair, but add additonal epoxy to any low areas as needed, rather than sanding too much off the high spots.

Either way should look fine, and will result in a good boat.

Old Yeller



RE: Sanded through fiberglass

when sanding through the glass for a small section, both approaches are valid.  to a large extent, its about how much time you want to put in and what created the problem in the first place,

it's important to try to determine is why you sanded through. 

if you sanded through becasue you had a high point/bulge in that area (and the area is now fair becuase you sanded through), a couple coats of epoxy will be fine and easier to work with.  otherwise, if it is fair and you put a patch over it, you will simply sand it off again (or create a bulge) if you put cloth over it without taking it down a little bit before you apply the patch.

if you got a little agreesive with a sander and created a flat spot, than a patch will go on easy and be easier to fair in as the thickness of the cloth will fill in the flat spot.

how can you check to know what is going on?  a stiff ruler or a piece of scrap okoume that you can bend over the surface will help you see what issue you have and help get the surface right prior to picking your technique for fixing this.



RE: Sanded through fiberglass

One other thought, Scott: Sanding through fiberglass sometimes also happens where the glass did not get stuck down properly, and lifted away from the wood. In that case, there probably aren't nearby low areas that need to be filled, and a simple fiberglass patch can usually be applied and easily sanded fair.

Old Yeller

RE: Sanded through fiberglass

Thanks for all the great advice. I had two issues with the fiberglass. One was as I described and it was due to poor control and impatience with the orbital sander. It was an area that was vertical and I must have been tilted to one side. It is small enough that I think I will just try epoxying as described above. 


The other problem was with the end tape over the bow. I had some air bubbles trapped under there that I didn't think would be a problem but as I was sanding bits of fiberglass crumbled away. I just sanded smooth and retaped the bow. It should be ready for ramming a battleship when I'm done...


It is the mistakes that happened way in the beginning that I am paying for now. 

Next boat will go much easier, right?

RE: Sanded through fiberglass

"Next boat will go much easier, right?" Absolutely. Even with thorough instructions and solid advice there really is no substitute for experience, which begins to accumulate as soon as you begin.

Old Yeller

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