Layering Polyester Resin

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Jarred

Jarred

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Hello all and thanks in advance for answering. I have read the library including the snakeskin casting tutorials.

I am working on my second attempt at casting snakeskin blanks. I made a "resin saver"-type silicone mold based off of the size of various blanks I want to cast. The snakeskin-wrapped tubes were painted with Castin' Crafts polyester resin and the rest of it put into an old ultrasonic cleaner, then poured. I touched up the amount of resin in each of the wells after pouring, and then put the mold into a pressure pot at 50 PSI overnight.

The resin looks great around the snakeskin-- however, the resin in all of the blanks sunk more than I am comfortable with leaving as-is-- I need to pour some more into each well. My question is about the timing of the second pour. Castin' Crafts documentation says don't wait until full cure, some other resources say wait until cure, rough sand, then layer. I'm concerned that I will not be able to get back to the blanks before they have fully cured. Does anyone have any experience in this problem?

Thanks,

Jarred
 
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Will say this I use Silmar41 resin and have casted over resin 24 hours after first cast with no problem. About 15 years ago when I got into pen turning I started with Cast-n-craft resins and made bottlestops with coins floating in them. This required a couple pours but what I would do was make the second and third pours right after the resin kicked in previous pour and had no problems. Now I have no other experience with later pouring with that stuff. That back then and probably still is a different formula than the Silmar resin so all I can say is give it a try.
 
Thanks for the complement Don. As far as the question goes I've done multiple cast with P.R. and had great results. I haven't tried to suspend an object but I have done it for the same reason your asking about. The only thing I did before recasting was to take steel wool or scotch bright and knock the glassy sheen off the blank. That was my thinking on maybe giving the new resin something to bond to without creating scratches that might show up after the recast. Good luck! One other thing. If your going to be doing a lot of casting I'd think about purchasing a good mold. If it's going to be once in a great while then I understand. In the long run I don't think it's worth the frustration touching up or redoing blanks when you could be just one and done.
 
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You have two choices when layering polyester resin pours:
  1. Pour the next layer after the prior layer has set but while the surface is still tacky. That way, the next layer will bond chemically to the prior layer. This results in the strongest bond and is generally the preferred method.
  2. Wait until the prior layer has set and the surface is no longer tacky. Then scuff the surface with 320g sandpaper (or equivalent), clean it, and pour the next layer. The next layer will not bond chemically to the prior layer. Scuffing the surface is necessary to give it some "tooth" for a mechanical bond to hold on to. This method produces a weaker bond than above.
I hope that helps,
Eric
 
Thanks everyone for the responses, I appreciate it very much. I will run some steel wool over the blanks and hope for the best.

Jarred
 
PR is made to take layered pours. My only suggestions would be to get some Silmar 41 poly resin from a dealer. This will insure fresh resin with the longest shelf life for your use. I've recast poly resin Blanks months after the initial pour (to fix chips or breakouts) with no problem. I've even recast snakeskins that didn't work the first time, after soaking the bad blank in acetone to recover the skin. Good luck!
 
John,

Great information. I have heard of Silmar 41 and will check it out. Good tip on recovering the skin as well.

Jarred
 
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