Ready to throw in towel - But I'm stubborn.

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carlmorrell

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May 14, 2013
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Beginner at casting. Experienced at screw-ups. I figured why whine in the forum, I know what I am doing wrong? Do I?

I am using the silicone resin saver molds. Cast-in Craft PR. At most, I need to mix 2 ounces to fill two casts. I am heating my garage to 75-80 degrees. Yes I know that's hot, but I assume I need the warmth to keep the resin flowing.

Yesterday I used 9 drops, and the resin hardened in only a few minutes, cloudy and full of bubbles.

Today, I used 5 drops, (that'hs 2.5 drops per ounce). After I poured the resin, it was hard in about 5 minutes. Hardly enough time to vibrate the bubbles out. And the resin is still cloudy, though not as much as before.

So tomorrow, do I go as low as 2 drops? Or give up, and admit defeat? I would like to add, every time I try to cast something, I have several hours into the blank preparation. I have f-d up stamps, watch parts, and now my idea for family Christmas presents. I am running out of runway.

Rant off.

I am thankful for having such a rewarding hobby, and a universal support group.
 
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The times you are getting seem very fast for the amount of MEKP, UNLESS you are heating the resin. If you are putting the resin in a hot water bath or otherwise heating the resin and / or molds before and / or after adding the MEKP then that would significantly shorten the gel time. More heat = faster cure.

With my shop and resin in the low 80s, I get about 10 minutes before the resin gels with 10 drops of MEKP per ounce. I'm using different resin (Silmar 41) and my MEKP could be older, but with only 2.5 drops per ounce I would expect a much longer time to gel for you.

Did you try doing a resin test? Pour an ounce in a cup and add the recommended amount of MEKP. Nothing else, just the resin and MEKP.. Start timing from the time you add the MEKP. Stir for about 20 seconds. Set the cup on the counter at room temp. No hot water bath, no vibrating. See how long it takes to gel. You can tilt the cup from time to time to see how it's going, but otherwise leave it alone.

Maybe that will help reveal what is causing your quick cure.

Ed
 
PR hardening time is primarily controlled by temperature, the promoter(s) mixed into the resin, and the amount of hardener (MEKP). Whatever the cause, your casts are setting very quickly. I'd try lowering the temperature and reducing the amount of MEKP.

If you keep having trouble and want to come by, let me know. I have a bunch of Silmar 41 I need to use up before it goes bad.

I hope that helps,
Eric
 
Yesterdays failure, I did pre-heat the mold, water for the vibrator, and the resin. I used a non-contact thermometer, was looking for 90 degrees f., and kept a close eye on things.

Today, I heated nothing. Maybe my resin is old? I bought it 2-3 months ago, but who knows how long it was on the shelf. The can looks pretty banged up from the store.

Eric, we have a lot of gossip to catch up on. Either that, or you have been "retired" so long, that your last job is just a fading memory.....:wink:
 
This isn't rocket science. I just did a 4 quart casting on a weird tropical wood trunk in a 1 gallon paint can...one cup at a time, 7 drops per oz. Not one single issue. 15 pen blanks in WW, 7 drops per oz...not one failure. Dozens of PR castings...7 drops per oz, no failures. Tons of info everywhere and then there is just plain good practice over and over again. No one can get it right for you.
 
I vibrate and heat the resin before I add 2 drops of mepk per oz. By the time that's done I have my mold heated and ready to be poured. When you mix the mepk and resin stir slowly so you don't mix in bubbles. Pour the resin in the mold at an angle so any air can be pushed out by the rising resin and I use a small wire to work out any remaining bubbles. Not perfect by no means but gets the job done. I also cast embedded objects in vertical molds so when I stand the tube in the mold I try to put the end pointed upward that will seem to trap the most air.
 
One thing that hasn't been said or asked is what it is that you're casting. I read the part about watch parts and stamps...Is there CA involved...was it fully off gassed? Was there any type of paint or water based media that was uncured? It might not be your methods but the media involved.
 
I appreciate the posts that are constructive.

I have read every article in the IAP libarary more than once. Talked to more than one person that has worked with PR. I even perused eti-usa.com website.

I have composite (carbon fiber/fiberglass from Sollar composites) sleeve wrapped around the brass tube, and secured with CA. Let is set for a day before proceeding. I have silk material, that I applied several light coats of acrylic sealer (mod podge) and again let set for a day. The silk material was attached to the composite with CA. Again allowed to cure for a day before I attempted casting.

Today (or tomorrow), I am going to buy a new can of PR. Thanks for the suggestion that I do a sample mix, and check the cure rate. For my own sanity, I am going to compare the older can to the new one.

I am going to refrain from commenting on the less than constructive posts made.
 
Castin Craft is not bad---but any hobby store would make me nervous. With several thousand sku's, there is no way to know how old your can is (of Castin craft, not the can that keeps getting bigger).

An old can could easily create inconsistencies.
 
I've used the mod podge before when I was doing stamps and I always got cloudy results. As noted, you may have old resin, moisture issues, or issues with the gassing. When I cast pens in the past I heated my resin as well so I would say, trash the mod podge and use thin CA. Let that stuff gas off for a couple days to be safe, then cast. Also, get a new batch of resin
 
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