Hi I went and jumped on a deal on craigslist for a 55 gallon barrel of silmar casting resin… SIL94BA-870 is the product code… It is a PER. It was never opened still sealed but had been bought back in 2008. I tested a small batch and ended up with some rubber basically… after a day of curing with the suggested 2% catalyst. Now the MEKP could be bad being It came with the barrel. I will try some fresh stuff. I read on one of the posts here somebody suggesting mixing it up via some bubbling process thread here http://www.compositescentral.net/showthread.php?t=528
I have also read the idea of adding some cobalt to it… anyone have any idea where to buy it? Anyone else have any suggestions for me? I dont want to have to take this barrel and just drop it off at hazmat instead of utilizing it. Thanks!
So far of all my searches for cobalt online it is impossible to find a company in the US selling it… anyone got an idea? or maybe some around for sale? Still trying other options. thanks.
ok made another test with what I thought to maybe be newer mekp. this time I left it in the sun and it turned yellow… as well I believe I used way too much hardener… what causes extreme yellowing? Would it be from too much hardener? or that it was in the sun? Preforming another test with recomended amount of hardener. I would like to try mixing with the bubbling method but I am afraid of the moister problem people have mentioned. been searching the forums here I hope I havent been too annoyingly Newb here. Thanks.
Cobalt (6% cobalt napthenate) is an accelerator. You can get it from Mahogany Co in Mays Landing NJ for ~48$/gal. I don’t know about PER, but for VER we use, it’s around 0.05 to 0.1%/wt. depending on the gel time wanted.
Not sure if it will help your old resin. If it’s too thick, maybe add up to 5% styrene to thin it, then do your mixing by the final weight.
The cobalt will also add color to the resin, it is blue!!
I do NOT like the idea of bubbling the resin to mix it!!! That would just introduce air into the resin, and leave you with, well…bubbles!
Very probably your MEKP has gone bad. It is prone to degradation, especially in (sun)light.
If the resin is still workable, the geltime might have drifted somewhat, but it should not pose any problem.
Adding too much MEKP indeed turns the stuff yellow (residual styrene) and undercures the polyester. When MEKP is mixed into polyester, it forms radicals, which react with the cobalt, which in turn reacts with the polyester, and the cobalt is freeed up again. Too much MEKP will make too much radicals, and these react with each other, stopping the process.
Add 1-3% of MEKP, not less, not more, unless you know exactly what you are doing. Starting with 2% is always good.
There are also peroxides with faster final cure, but you could also add some other promotors to achieve a faster final cure. But first get fresh MEKP to experiment with.
so I realized that I was a whole decimal point off… so I had been adding 20% catalyst!!! haha… wow I didnt know my math was that bad… so I am testing a new batch and crossing my fingers 
Thanks for your help guys…
20%??? That’s a lot!!! 
No worries though, I find myself messing up the simple math now all the time. Let us know if it works now that you caught the error.
Success!!! got pretty rock solid clear resin in only about 30 minutes! I am excited to finally get started on some projects! So what I did was added about 40 drops catalyst from a tincture bottle dropper to 100 ml of resin… I figured that would be about 2% if 20 drops = 1ml. Is this how yall sort of figure it? the resin got really bubbly though so maybe less hardener would be better? I am excited… I was worried I bought bad resin… can yall believe I bought 55 gallons for 160 bucks?
20% and it didn’t exotherm? Maybe the yellowing was caused by heat degradation! Woo. This is why I double check everything AND weigh by scale, not drop size.
interesting… what kind of scale do you use?
shrugs I know we have a few Mettler-Toledos around. Something with 100th gram accuracy, depending on your average part size. For 1kg resin, I try my best to put in 0.01% 2,4-P in the resin, and it is close enough. I wouldn’t get anything less than 10th gram accuracy. Again, if you are only doing small parts, you need better accuracy. Maybe a graduated pippet system would be cheaper than a lab scale? See if the manfu. has volume/weight charts so you can measure volume and calculate the weight of the few drops?