Thursday, May 08, 2008

Epoxy Sanding

Once the epoxy had hardened, it was time to sand in preparation for varnishing and painted. My plan all along was to varnish all of the interior and the exterior of the transoms. The rest of the exterior would be painted in a dark green color to match the hull color of our Potter 19, "Promise".

Of all the steps in building the pram, this is the one I underestimated the importance of getting right. I had assumed that any flaws with the epoxy coating that sanding didn't remove would be taken care of by either the paint primer or by multiple coats of varnish. While this was true for the smaller imperfections, it wasn't true for the larger blemishes, such as drips and runs in the epoxy or where fiberglassing had gotten "wavy". In hindsight, I see that I should have spent more time sanding to a uniform level. This would have resulted in sanding through the epoxy in spots (which happened anyway), but I should have been not afraid to add more epoxy coats and re-sanded those. In short, I should not have considered epoxy coating and sanding as separate steps, rather as a single effort to produce an absolutely smooth and even, fully sealed surface ready for paint or varnish.

But I didn't realize this until I started painting and varnishing. Oh well. Next boat.

I started with the interior (since it was what I just finished epoxy coating). For the first time, I used my random-orbit sander (connected to my shop vac). As I feared, it resulted in my sanding through the epoxy to wood or fiberglass in spots. I could only use the sander on the bottom of the inside and on the seats. I did wind up recoating the seats and the bottom with more epoxy. Those were the surfaces that turned out the best - I just wish I had recoated more places. Also, I didn't re-sand with the sander, opting to hand sand the recoated surfaces. I think this was a mistake. The sander did a much better job. I was just too afraid of sanding too much. Instead, I sanded too little.

Eventually, I got it tolerable enough and flipped the boat over to sand the exterior.

The exterior was a similar story, except I did use the sander for the first pass (150 grit). I sanded through the epoxy in spots at the edges of the laps. I recoated, but here I made another big mistake. I only recoated the edges where I had sanded through. I should have recoated the entire exterior again and resanded with the power sander. But I didn't and wound up having an uneven surface on the outside of the panels. At this point I was still assuming that the primer and paint would cover this up.

The interior, after sanding epoxy coats

1 comment:

Harry said...

looks great, I'll check back later to read more.and ya paint don't cover nothing. Harry