# Silmar 41 Casting



## jasonb (Dec 26, 2018)

I typically cast small objects with alumilite. I decided to adventure into polyester resin to cast some hybrid lamps. I've casted a couple hybrid blocks so far and both attempts the resin cracked. Roughly 32oz of resin went into each and followed mfg hardener amount. I assume the resin is cracking from too much generated heat when curing? So either thinner and multiple pours or less hardener, should help?
@rocky1 

Pic #1 is the first hybrid light I made and luckily the crack in the resin was close to one end so I just shortened it. I also dyed the resin blue and white with alumilite dye, but as you can tell blue color didn't stay (later I read that alcohol based dye doesn't work)
Pic#2&3 is the 2nd hybrid light and you can see the crack right in the middle.

Reactions: Useful 1


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## Jamesis (Dec 26, 2018)

*Well Hellfire and Brimstone, I died and went to . . . wait a minute . . .

Just kidding, that's one awesome lamp*

Reactions: Like 2 | Agree 1 | Funny 1


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## Jamesis (Dec 26, 2018)

Just out of curiosity, what do you sell those things for. I'm guessing around $50-60?
Are they LED lights? USB Powered?


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## jasonb (Dec 26, 2018)

Jamesis said:


> Just out of curiosity, what do you sell those things for. I'm guessing around $50-60?
> Are they LED lights? USB Powered?


Only finished one so far too see how'd it turn out. 2nd one is turning into a belated xmas gift. No plans to make many more and sale. I used an ikea led on the first one. Deciding if I want to go same route on the 2nd one.


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## Jamesis (Dec 26, 2018)

Seriously Jason, You could sell those on Etsy!


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## rocky1 (Dec 27, 2018)

Top one is way cool Jason! Now if you just knew what you did to make it work like that, it would be cooler yet. Right? 

Not sure what to tell you on the crack. On your other pour, did it happen to crack at the narrowest point in the casting as well? Looking at that one, I suspect the point in the middle, where it cracked, likely cured and cooled before the two sides. As the sides continued to cure, cool, and shrink, it set up stresses that pulled toward both sides causing it to crack. Haven't ever noticed that problem; not going to say I haven't had it, but I haven't seen it. But, by the same respect, I haven't done any 32 oz. pours into a single mold. Pouring that laying down would obviously be the most reasonable approach, but I wonder if pouring it standing on end might not work better. In that manner, circulation in the mold as the resin cured, would work through the narrow spots and prevent them from curing faster than the wider areas.

Otherwise... I have mixed feelings on reducing catalyst in dyed pours anymore. From what I've seen, the longer it takes the resin to cure, the more apt you are to see change in colors, disappearing dyes, and other dye related issues. It needs to cure as quickly as possible, to prevent change in color. But, yes reducing catalyst and curing slower would maybe help, but I think pouring it standing upright would be a better plan. 

Next thing is however... Those purty little swirls in your pearl are going to change if you stand it upright and pour. That ring of sparkly pearl around the edge of the blanks in that middle picture, is created by the resin turning over in the curing process. If you cure it on your work bench, you can watch it do this. Good or bad, it's going to circulate differently standing up.

Reactions: Informative 2


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## rocky1 (Dec 27, 2018)

Some consolation on the changing colors... - you are most certainly not alone there!


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## jasonb (Dec 27, 2018)

On the first piece the crack occured near the base, so at the widest point. I thought about pouring standing up, but at that point it would fit in my pressure pot and I'd switch over to alumilite. I'll give it another shot and try a sandwich pour and see how it goes.


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## Tony (Dec 27, 2018)

Dam cool Jason!

Reactions: Thank You! 1


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## Chris S. (Feb 17, 2019)

Do you need to use a pressure pot with silmar? How bad is the smell? Very cool projects.


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## jasonb (Feb 17, 2019)

Chris S. said:


> Do you need to use a pressure pot with silmar? How bad is the smell? Very cool projects.


No pressure pot needed with silmar. In the garage if closed up, I were a paint respirator dual cartridge mask due to the smell.

Reactions: Thank You! 1 | Agree 1 | Informative 1


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## rocky1 (Feb 18, 2019)

Silmar is pretty ugly in respect to smell Chris. Not something you want to cast with in the house. 

Pressure pot is not necessary, warm your resin before casting, mix gently, pour slowly, avoid as many bubbles as possible in your mold. Alumilite, is a urethane resin, it creates bubbles in the curing process. Silmar a Polyester resin, does not. Crank the blade down, below surface, on your table saw, set your mold on top, and let it run.

Reactions: Thank You! 1 | Agree 1


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## Graybeard (Feb 18, 2019)

Thanks for sharing. We can all learn something. I'm about ready to take the leap using alumilite. So much to learn.

Reactions: Like 1


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## Schroedc (Feb 18, 2019)

Silmar like almost all of the Polyester resins has some shrink to it so what happened was that during the cure with that much resin the amount of shrink was too great and the tension caused the crack. I have cast slabs of resin (No wood in them) 3 inches wide, 1 inch thick, and 14-16 inches long. As they cure they'll shrink up to a 1/4 inch or more in length. Your solution could be multiple pours, 3/8 to 1/2 inch thick max would probably be a good starting point to experiment with, also it'll take longer to cure but cut your catalyst back by 10-20% or so and see if that helps.

Reactions: Thank You! 1 | Informative 1


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## jasonb (Feb 18, 2019)

Schroedc said:


> Silmar like almost all of the Polyester resins has some shrink to it so what happened was that during the cure with that much resin the amount of shrink was too great and the tension caused the crack. I have cast slabs of resin (No wood in them) 3 inches wide, 1 inch thick, and 14-16 inches long. As they cure they'll shrink up to a 1/4 inch or more in length. Your solution could be multiple pours, 3/8 to 1/2 inch thick max would probably be a good starting point to experiment with, also it'll take longer to cure but cut your catalyst back by 10-20% or so and see if that helps.


Makes sense. Going to try again next weekend.


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## Chris S. (Feb 18, 2019)

Thanks guys for info. Figured would smell bad but was hoping not.


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## Rocking RP (Feb 19, 2019)

Very cool idea. Hope you figure out solution to the cracking problem.


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