Strategy for applying this surface coat


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quinn
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My plug is done and I'm about ready to lay up a mold. This will be used for prepreg so I'm using premium resin tech rdr-1902 high temp surface coat and rdr-3212 resin. I have some concerns with the surface coat. It's a bit thicker than I imagined but I guess that's good so it won't run, however after mixing a small test batch, it seems pretty slow to release air bubbles. As you can see in the pic of my plug, there are areas with vertical walls and even a few areas of negative angle. For air to release from the surface coat as I brush it on, these bubbles need to rise to the surface to pop right? So any areas that are beyond vertical with a negative angle, I would think are gonna have a hard time releasing air. I picture a bubble just rising up against the surface of the plug and staying there. I'm wondering if I should apply the surface coat in partial areas with the plug oriented so surface coat I'm applying is face up, allowing better release of air bubbles.  Do I need to bother? Or can I just brush it on the whole thing as it sits in the pic? Looks like pics got rotated 90 degrees, the pointed nose is up
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quinn
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KLComposites - 2/19/2019 2:09:22 PM
I make wet-laid molds out of fiberglass, compensating for the reduced stiffness with extra thickness. The glass, being translucent when saturated, allows me to see any voids between the surface coat and the first several layers of reinforcement that need to be rolled out. Any air, no matter how small the bubble, will expand as its heated in the post-cure cycle and pop through the surface coat, leading to what you've described - burst pinholes and/or blisters.

Ah, that makes sense. The waviness/dimples I saw did appear to be positive bumps when sanding. Would make sense that expanding air would push these out. I remember thinking when I was doing wet lay that I can't tell if there's air in the laminate, definitely easier to see with fg. I always thought the issue with a fg mold for cf parts was the difference in expansion rate? Is this not a concern?
Anyway, I think that makes sense as a reason for the dimple shapes, but not so sure about the couple patches of little micro air pockets. I kind of doubt the surface coat got soft enough for little bubbles to actually flow through it from the laminate. I'm thinking those micro voids were more likely in the surface coat to begin with.

Edited 6 Years Ago by quinn
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