Silly question time ... sanding glass cloth?

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Silly question time ... sanding glass cloth?

Postby SMHolmans on Sun Oct 14, 2018 12:54 pm

Evening from wet and windy Oxford in the UK.

I'm just a few days into my PocketShip build and on a steep learning curve. I've not worked with fibreglass cloth before and I'm wondering, just how tough is this stuff? The reason I ask is that I have glassed the inside of the centre board case halves and I am now sanding them smooth - is it easy to inadvertently sand right through the glass, and would it be obvious if I had? It's 200g, as supplied with the kit. I'm using a good random orbital sander, with 120 grit.


Many thanks!


Steve
SMHolmans
 
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Re: Silly question time ... sanding glass cloth?

Postby TassiePete on Sun Oct 14, 2018 4:32 pm

Hi Steve,

If the cloth has been laid down nicely (no creases in the cloth or bits of wood under the cloth), and the weave is properly filled, then sanding is easy. As long as you keep the sander flat on the panel, you won't cut into the cloth. I usually started with #80 and then finished with #120. If you do get too close and hit the cloth, it will be very visible. The area will turn white and fuzzy. Very small areas (coin size) away from the edges of the panel, you can ignore - just put couple of layers epoxy over it and sand it smooth (once it's painted, nobody will know). If it is a bigger area (or 'structural', near the edge ), you may want to cover the area with a patch over the top. Let it overlap all around by a couple of inches. A couple of filler coats of epoxy and the patch can be faired in easily.

I used credit/membership-cards to wet out the cloth and to collect 'surplus' epoxy. Don't use too much epoxy when wetting out, or the cloth will float up. Spread and then remove as much as you can without getting white patches (starved of epoxy). At this point you determine how much sanding you will have to do later.

When filling the weave, I found it much better to roll on 3 or 4 thin even coats of epoxy rather than 2 thick coats. Sanding panels is painless and quick, if the epoxy isn't full of drips, lumps and bumps.

Before sanding, always (?) give the panels (or whatever) a good scrub with warm water and a kitchen scour to get rid of amine. It saves on sanding disks (and frustration). After you have done a few pieces, it will become easy ...

Cheers,

Peter
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Re: Silly question time ... sanding glass cloth?

Postby SMHolmans on Sun Oct 14, 2018 5:59 pm

Wonderful! Thanks for the advice. Very helpful.
SMHolmans
 
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