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Hello all,
I'm building the PMD and am applying the sencond coat of epoxy to the strakes. On one side, after sanding, I brushed off the dust, blew it off with an air compressor, then wiped down the strakes with denatured alcohol to ensure I removed all the dust. I only waited perhaps 15 minutes (while I prepped the epoxy) before applying the 2nd coat. Afterwards I worried that I didn't wait long enough, although after several days all looked good. After sanding that side I prepped the other side the same except I used a wet cloth to wipe down the strakes to remove dust. I waited perhaps 30 minutes (until they looked dry), then applied the 2nd coat. But I experienced a fair amount little circulular areas where the epoxy appeared not to stick. I went over those areas a few times, and they seemed better, but a few remained (see picture link). Should I be concerned? How do you all prepare your strakes before epoxying?
https://www.dropbox.com/s/jap7gnlfeo9o9xq/2020-02-17%2012.05.05.jpg?dl=0
4 replies:
RE: Post shanding prep strakes
Thank you spclark. I think I was worried the alcohol wipe may not have been the best way...I should have asked first. I think I will likely have to sand down most of the epoxy and vaccum then alcohol wipe, then re-apply. Also I will stay away from the air compressor. Thanks for these tips.
RE: Post shanding prep strakes
yeah, regular compressors always have moisture and oil in the air. I'm in aerospace mfg and our business was consolidated into another unit. Our parts are very high tolerance (+/- 0.0001" in places) and subject to corrosion, so we always had very high spec compressed air in the shop, but the new location didn't do any of that kind of work, more of a stone age kind of factory. We forced them to tear out all their ancient filthy compressed air lines and put all new compressor, dryer, filters, plumbing in. And they thought they'd save money. :-)
I've been using a Shop-Vac with a special order HEPA filter (not the standard) and it works pretty well to get the dust off the work and stay in the vacuum, but I always wipe down with a clean rag after. I've never had the Mas epoxy blush, so I don't generally wet wipe. The ShopVac hose fits both my sander and my jig saw to get a lot of the chips/dust as they are made. Hand sanding, I'm usually holding the vac hose in one hand and the sandpaper in the other. Now, if I could just stop dripping epoxy where I don't want it...
RE: Post shanding prep strakes
Thank you Mummichog...one of these days I will learn to ask FIRST...back to sanding...uggg :-)
RE: Post shanding prep strakes
» Submitted by spclark - Mon, 2/17/20 » 6:39 PM
I can't clearly see what you're trying to show us all in that image you Dropboxed (severe glare off something destroyed detail!) but as a general rule it's some kind of contamination that causes epoxy not to adhere & 'self-level' prior to cure stage.
You got it right on the first side, what caused you to change method for the second?
If this last application cured hard and as thoroughly as you've seen it happen I'm not inclined to suggest it was improperly mixed, which can effect the same failure appearance as surface contamination... but maybe that's a factor too?
Could also be that you lucked out blowing dust off with a compressor stream if there was any water/oil blown out with the air out of your tank. Alcohol wipe likely removed what contamination may have happened that then left behind what could have been in the air stream for the second side prep when you used only a water-wet wipe for dust removal.
I'd avoid using compressed air for dust removal. Chances of contamination from oil & water in the airstream are just too great. Besides you're not removing the dust but merely blowing it someplace else. Vacuum cleaner much to be preferred, then an alcohol-wipe.