Glen-L.com

Hi Gents
I am building a Zip. I have read that you should saturate the hull with epoxy before you fill in screw holes etc. with hard setting putty. I have also read that you fill in first, then saturate with epoxy. I have also read that you should never sand bare plywood. Can someone please tell me if it really matters or not.
Many thanks
William

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Moneypenny UK

I encapsulate then fill. My logic (likely screwed up) was that the filler would be too thick to properly encapsulate the damaged grain around the heads. In the event of a screw-pop the wood would still be sealed.

Sanding ply myth likely stems from thin veneers on the surfaces, and the risk of sanding through them.

I found it better to work with ply that was encapsulated, especially for sanding. Bare ply is much softer than any of your fillers/epoxy etc. Therefore if you are working with encapsulated wood, the sanding surfaces are all about the same and I got better smoother finish.
I encapsulated before filling or sanding anything, screwholes or otherwise.

Hi Guys
Thanks for taking the time to reply. I agree, I will encapsulate before filling. I just wanted confirmation. The 'experts' in some books have conflicting opinions.
William

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Moneypenny UK

Hi William,

Not sure what ply you're building with but in the case of Doug Fir & Larch (very common) the gaps between growth rings (different tone) are of varying hardness... enough to make smaller drill bits wander, even. Sanding on such plywood where the rings have been "peeled" and laid up into ply can result in "scalloped" surfaces where these variances resist abrasion at different amounts.

Saturation with epoxy tends to level out the playing field.

Edited to add: As you probably already know, curing epoxy produces an "amine blush" which doesn't stick well to other physical and chemical structures. It's removed by a number of means, but if you try to stick putty to amine blush you'd have problems. Since the blush is going to be located in a screw hole... well you see the difficulty.

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Avoid Haste.