Sanded through glass - now what?

I thought I was being careful, read the instructions, read books, read several posts (here and here) but I am pretty sure I went through the glass on the bottom. There were some slight divots and i was trying to get a consistent gray, but ended up too deep all around the divots. As far as I can tell, I went too far. I never saw strings or wood shavings coming up in the sanding, but I think I should assume that I am into the glass and possibly even through it? This is most of the bottom of the boat (Shearwater 16 hybrid, first time builder). So, should I sand the rest of the weave off and basically start the bottom again, or am I ok to lay on more glass and do two layers of epoxy on that (obviously doing a better job this time)?

I can post pictures later if that will help, but I had a lot of drips in my epoxy, so it was a real challenge to get it smoothed out. Obviously I would prefer not to do glass and epoxy again, but I want this to be right. I will be lacquering it later, btw.

Thanks in advance,


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RE: Sanded through glass - now what?

Yes, picture(s) would help. Sanding into 'glass cloth won't raise any 'strings' as such, you'll just be reducing the fibers to dust that looks like the dust from sanding epoxy.

Usually you can see the weave though once you break into it, well before you've removed it entirely... unless you're using a powerm sander, maybe with too low a grit paper, removing stuff too fast for control.

You already have a good idea of what bare wood looks like, having started with that before you began to cover it with epoxy & cloth, right? Do the divots (these are depressions, right?) you were trying to sand out look like raw wood?

Beginners often encounter problems when the 'glass cloth 'floats' on top of a puddle of epoxy resin. Once the resin hardens you have a high spot with the 'glass close to the surface. Sanding that away will take off the cloth before you get to the resin underneath.

In any event, it's fairly straightforward to add 'patches' over things like this if you're careful to both make the patch big enough to overlap maybe an inch of the 'glass you know is there, as well as feather-sand the edges of the path before building up the entire surface to a uniform depth of resin. It may never look right to you but even finished 'bright' (varnished) it ought to look just fine to almost all casual observers. If you plan on a painted finish no one but you will ever know the patches are there.

RE: Sanded through glass - now what?

Everywhere I have looked, I can still see weave, so I'm really not sure now. Here are a bunch of pics -- hopefully they help. Clearly I let it go on too thick in places and the drps were pretty bad...

The divots are lower spots where it is still shiny. I do have a couple of places where there are small bubbles or a little floating, but not much.

On a related note, if I have a spot where it is all gray but there is a little area that is shiny and clear, but it is all level, is that ok, or am I trying to rough up those clear spots, too?

Thanks again!



RE: Sanded through glass - now what?

In your picture above, mostly what I see is a thick layer of epoxy that has filled the weave surrounding some areas where the glass is saturated but the weave not filled. It looks as if you had drips all across but especially on the lower left.

I don't see any spots on that picture where you've obviously sanded through, What I see is stuff like the 2nd 3rd pictures in the series below. Places where you need to add more epoxy before sanding it smooth. The vast majority of your picture is more like the 5th picture in the series, except with way thicker epoxy.

I'd suggest that you use raking light so that you can see if that's the case. Also, try wiping down the areas with denatured alcohol to see what it would look like if you varnished it right now. If the weave disappears, you have something like the 5th picture. If it fades but not completely, the the 1st or second pictures. If it doesn't fade, then you've sanded into the glass.

The way I'd fix this if it was my boat is to identify the low spots, paint only those with epoxy and then use a longboard to sand the whole surface. I'd repeat the entire process until the whole boat was smooth and dull.

Finally, if you haven't done so, read the Shop Tips article on filling the weave. That's where the pictures came form.

Good luck,


PS - if you click on your picture it will enlarge.


RE: Sanded through glass - now what?

Pics are a big help SD, thanks. You're doing fine with this.

Those 'divots' you see are the opposite of the drips that sit high on the 'glass cloth, your sander left them untouched. Drips show an untouched border around them after being touched lightly by sanding.

The divots need to be sanded very lightly before re-coating. Synthetic abrasive material like 3M's Scotch-Brite is a good choice for this as it doesn't remove a lot of material and will conform easily to the countours of depressions like this. Sandpaper can too if it's 'broken' first by dragging the back side of the paper first in both directions across a hard-edged workbench. This makes the paper more supple making it conform to the uneven surface without digging in. (Easier shown than explained but I can't find anything on the web to illustrate the technique.) The idea is to pull the backside of a sheet of unused paper across a hard edge so thst the paper fibers and glue are flexed. Do this twice, re-orienting the paper 90° for the second pull so it's 'broken' across both length & width.

Those drips can be sanded away with the longboard technique Laszlo suggests is appropriate for leveling things after the low spots have been filled. It's tricky to do with a power sander yett with practice and a careful approach it's not impossible.

The big item is obtaining sandpaper of a size that will cover a longboarding tool without seams. Auto body supply shops ought to have what you need for this operation, or you can find it on-line.

I don't see any indications in your pics that you've gone through the 'cloth. In the one image showing puzzle joint there's a small section where the cloth may have been sanded into. With the alcohol-wetting technique Laszlo's suggested you'll quickly see what that area will look like with more epoxy on it or if you go straight to varnish. Were I you I'd add another coat of epoxy to protect the 'glass then sand again to level things out before varnishing.

RE: Sanded through glass - now what?

Thanks a ton - both responses really help. I have a 1' hand sanding plank but will look into a longboard. Will get it cleaned up and do some epoxy touch ups. The sides and bow/stern were a challenge and that's where almost all my drips happened. I think I just got in a hurry and also wasn't working in good enough light. 

RE: Sanded through glass - now what?

Taking on anything new for the first time, there's a learning curve. Enthusiasm can lead to that curve being steeper than it could be!

Working fast comes with practice. With epoxy it's a useful skill to develop but it takes time, particularly if you don't have a mentor you can observe at work who can slow you down a bit until you gain confidence.

I,m glad you're where you're at with this! You're learning the important bits both by DIY experience as well as what we out here can offer up when you post queries on the forum. 

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