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Sanding into the glass - how do you know?
This is my first glassed boat, a Mill Creek 13.
I've read the shop tips and about 150 threads about sanding. There are plenty of warnings about not sanding too deeply, but how does one know?
How do you know when you are sanding into or through the glass? After sanding off the "print through" of the weave, what indications does one see when actually cutting into the glass?
Wood dust is not the answer I want to hear. :)
13 replies:
RE: Sanding into the glass - how do you know?
THANKS Laszlo! That's exactly what I wanted to know, the indication to watch for.
Appreciate you checking in today.
RE: Sanding into the glass - how do you know?
Hi John,
On my CH16-LT, I had an obvious line where the deck cloth overlapped the side of the hull. I carefully sanded the lower edge of the overhanging cloth until it blended into the side of the hull and the line disappeared. I can feel a very slight ridge in a few spots, but for the most part, you can't tell where the deck cloth ends on the side of the hull.
This is my first kayak, so perhaps one of the more experienced builders will chime in with a better way to do this.
Mark
RE: Sanding into the glass - how do you know?
John,
What I described was the max sanding limit, the point of Sand No More. It's OK to stop sanding before that as long as the boat is smooth enough for you.
Mark,
Sounds to me as if you've got it. You can get rid of that ridge if you want by applying more epoxy on either side of the ridge, only, and sanding the area with a large sanding block. That will fill in the depression and sand down the ridge. But that's only needed if you're chasing the perfect finish. It won't make any difference in how the boat performs.
Laszlo
RE: Sanding into the glass - how do you know?
I was trying to get rid of the shiny spots, and I had four thin coats of epoxy on this surface, but, I hit the glass, Like everyone says can't get rid of it.
Should have laid the yak on it's side and applied the epoxy on a flat surface.
Here is a pic of what it looked like, and still looks like, only shiny.
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Hope that worked.
Ted B
RE: Sanding into the glass - how do you know?
John,
I meant visual smoothness, not tactile. My point was that you don't actually have to sand all the way down to just short of touching the glass. As the builder, you can decide at any point that you're satisfied with the finish and stop. That's what I meant by smooth enough for you.
The uniform cloudiness with no shiny pits is usually a better indicator than just feeling it with your hand (though you should do that too).
Laszlo
RE: Sanding into the glass - how do you know?
Keep in mind that the epoxy is not simply a coating over the fiberglass. When properly applied, the glass, as well as the outer layer of wood, are saturated with epoxy and become a single unit. Even if you sand completely through the glass in spots, you still have a waterproof barrier as long as you don't reach bare wood. The wood gives your boat shape and color; the glass, when saturated with epoxy, gives it stiffness and abrasion resistence; and the epoxy waterproofs it and holds everything together.
-Wes
RE: Sanding into the glass - how do you know?
Now that I understand what to look for, and have made it through the sanding process, I've made a blog entry with a series of pictures that might be helpful to others. See it at: http://www.bob-easton.com/blog/?p=1394
RE: Sanding into the glass - how do you know?
Just to add one more example of when it feels right to you. My first 2 Chesapeaks have one inch overlap with a very obvious (to me) edge, some frayed ends going off at odd angles, hundreds of drips of epoxy down the side. Rough sanded it, slapped on a few coats of varnish and went paddling. People always stop me at launches to say how beautiful the boat is. etc. I don't have a coffee table finish boat to compare to but I don't think it slows me down much. Boomarangs have little waves built into them to creat a better laminar flow. maybe my boat is faster? After 4 years of paddling and scratches and dings and a few sloppy patches, I think it is time to resand and revarnish. Maybe the drips will get a little less noticable with each refinish but I do not really care. To me it's a great way to get on the water, not a piece of art. If I finished it to well I might get to be so careful I would forget to have fun.
Ed
RE: Sanding into the glass - how do you know?
Bob:
Beautiful explaination and pictures of the levels of sanding required.
Your doing a great job!
I find hand sanding much easier than the noisy messy power sanding, you actually feel the cutting action and know when it is time to change the paper.
Ted B
RE: Sanding into the glass - how do you know?
Bob,
Thanks for the nice mention in your blog. Those are good pictures, showing exactly what happens as sanding progresses.I've always been in too much of a hurry to finish the sanding to be photographing then, so I'm really glad someone took those pictures.
Just one little nit with the text - when you first start seeing the weave pattern, the one that disappears with the wet cloth, you are not actually into the glass yet. Almost, but not quite. You're not in it until the pattern shows while wet.
Ed,
That's a good healthy attitude. There's a lot more to building a boat than the last 0.020 inches on the outside. Personally, I'm much more impressed by strength, stiffness per unit weight, durability, etc. - the things that will keep you afloat and get you back to shore in bad weather and rough conditions. No matter how smooth and shiny it may be, all that varnish does is protect the boat from sunlight. It seems really silly to me to spend triple the time it took to build the hull just to get the UV protector smooth. One day, if someone plies me with enough beer, I'll tell everyone my theory that coffee table finishes are the direct result of the rich oppressing the masses, but right now I'm already in enough trouble with the varnish mafia so I'd better go. :-) :-)
Have fun all,
Laszlo
RE: Sanding into the glass - how do you know?
Thanks again Laszlo for the "one little nit." I'll make that more clear.
All of my poxy sanding is now done. The shop has had a complete cleaning to remove as much dust as possible; sure needed it. Everything is as clean as I can get it. So, I'll start painting the bottom this afternoon.
RE: Sanding into the glass - how do you know?
» Submitted by Laszlo - Sun, 5/2/10 » 2:15 PM
Bob,
Just before you actually sand into the glass, you can see the weave. It looks a lot like exposed glass. However, if you wipe it with a wet cloth, it disappears, then comes right back after it dries out again. This is the point to stop sanding. If the boat's still bumpy, roll on another thin coat or two of epoxy and let it cure before sanding any more. You'll notice as you add epoxy that the weave disappears and stays gone.
If the weave does not go away when you wet it down, you're in the glass.
Laszlo