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Old 12-23-2015, 10:31 AM   #1 (permalink)
 
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Default SILMAR 41 -Can it go bad?

I purchased a gallon of Silmar 41 this past summer and it worked great for a while. Lately it just won't solidify. It takes days to get semi-solid. I'm sure I'm using the right proportions with the hardener. My garage is about 60 degrees but I poured and taken it inside and it still won't harden. When I first got it it would begin to harden in 10-15 minutes. It no longer sets up like that. Can it go bad after a while and could it go bad so soon?
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Old 12-23-2015, 10:55 AM   #2 (permalink)
 
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I would suspect the hardener before the resin.
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Old 12-23-2015, 11:05 AM   #3 (permalink)
 
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It's shelf life is 3 months. It is possible to last longer but they only guarantee 3 months. Try mixing it though. I heard from someone that the styrene will seperate over time from the rest of it.
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Old 12-23-2015, 11:17 AM   #4 (permalink)
 
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Kevin,

I'm having the same problem with my Silmar 41 right now once it goes below 60 degrees it doesn't like to set. Daytime temps are in the low 60's but night time is down in the 40's and I usually cast in the evening so it's not warm enough for it to set.

I've been trying to find a way to keep mine warm while in the pressure pot.

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Old 12-23-2015, 11:20 AM   #5 (permalink)
 
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Quote:
Originally Posted by brownsfn2 View Post
It's shelf life is 3 months. It is possible to last longer but they only guarantee 3 months. Try mixing it though. I heard from someone that the styrene will seperate over time from the rest of it.
Doh.... I should have thought of that before buying 2 gallons of PR in the Fall. Dang Ohio weather and unheated garage. I better get moving....
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Old 12-23-2015, 11:21 AM   #6 (permalink)
 
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Something else to consider. What and how much, if anything, are you using as pigment?
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Old 12-23-2015, 11:36 AM   #7 (permalink)
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Trukfixr has a point I find that blues really affect the set time.
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Old 12-23-2015, 10:16 PM   #8 (permalink)
 
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It could be the MEKP. If you shake it up, you should see bubbles on the surface for several minutes. If they go away similar to shaking plain water, then it's probably bad. I was told this by someone from US Composits.

If you think your MEKP is ok, try warming your PR in a warm water bath prior to using. I do this in the colder months, and it works for me. In fact it usually sets a little faster than in the summer.
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Old 12-24-2015, 09:35 AM   #9 (permalink)
 
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Typically, when polyester resin (including Silmar 41) goes bad, it starts gelling on its own, and eventually hardens in the container. As long as the resin is still liquid, it should still be good. I've cast Silmar 41 successfully, even when the can was partially crystallized and I had to strain out gelled globs.

Provided you store it in a cool, dry, dark place, MEKP should last almost indefinitely.

I suspect temperature is the culprit in your case. Silmar 41 is formulated for use at 70-80 degrees Farenheit. If the resin is much cooler than that, it will not gel (or will take very long to gel) unless you use very high amounts of hardener. I concur with the others who have suggested warming the resin. Silpak (for example), recommends heating their casting resin to 80F and the molds to 100-125F, with 0.5-1.5% MEKP.

When I cast Silmar 41 in the winter, I preheat the resin in my powdercoat oven before mixing in the MEKP. I find that casting under pressure slows the cure, so I also put the pressure pot somewhere warm while the resin sets (in the sun during the summer, by my heater during the winter).

I hope that helps,
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Old 12-24-2015, 09:43 AM   #10 (permalink)
 
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I only pour small amounts, max 3 ozs, at a time and use a coffee cup warmer (sometimes sold as a candle warmer) to preheat my resin. I start to heat it as I get my pigments together.

After I mix in my pigments I put it back on the heat and the warmer kind of pushes the bubble to the top where they either break or I skim them off. I then put it back on the heat after I mix in the MEKP. Just have to not turn my back on it, goes from water thin to gel in seconds.

I also sometimes put the mold back on the heat. I've had ready to turn blanks in just a few hours.
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