Need Help with Casting Resin Disaster

[pnolan48]

I admit at the start that I lost my attention when mixing casting resin to make a few small parts this afternoon. Instead of just a few parts, which would have required mixing 0.25 oz of each component, I decided to mix about 1.5 oz each, and also cast a few containers and skylites. It's hard to mix 0.25 oz together accurately; much easier to measure 1.5 oz.

So I didn't shake either component well, did wait a few minutes for the bubbles to rise, then didn't mix the two very well before pouring into the molds.

I knew within two minutes that a gooey disaster was underway. Of course it didn't set! Or rather, set partially, which is even gooe-ier.

Any ideas about how to clean out the molds? I've wiped them out with paper towels and made a few sacrificial pours (well shaken and mixed), but the crisp edges are now soft and gooey. I don't know if more sacrificial pours will finally clean out the excess goo. Should I just bite the bullet and make new molds? Man, these were nice molds--very smooth, with razor sharp edges. I'm hesitant to go into the molds with a solvent.

[central.vermont]

Just a thought Pete. But the first thing that came to mind was cleaning it with Goo Gone. Call me crazy but it might work! 

Jon

[jimmo]

With my last disaster like that, I used mineral spirits to clean out the goo. I took a shallow plastic pan (like you get with some takeout) and used a 1 inch brush to scrub the molds clean. They swelled a bit but after letting them dry overnight they were fine. After that I made sure I sprayed them good with mold release. My molds were SmoothOn Mold Max 30 (pink stuff).

[pnolan48]

Thanks Jimmo!

These are MoldStar 30 (deep blue). I was using SmoothCast 300 (I let it set 30 minutes, or until it is cool), as the molds for containers really don't trap air, so quick set is OK. My third (or fourth, I've lost count) sacrificial pour was SmoothCast 310, with a much longer setting time. I pulled one of the four containers after only four hours, and it looks like that pulled out all the gunk, with a marginally usable cast piece, lo and behold. I'll let the other three set overnight, as well as the skylite, and the four tiny booby hatches that started this whole disaster. The booby hatches mold is polyurethane (transparent amber) of about 50 stiffness--ah, the mistakes we make when we first start out, as these are some of my first molds.

Now, off to get the goo off of my hands! (Yes, I used gloves, but they tore, and this stuff gets EVERYWHERE all by itself.)

Let you all know tomorrow afternoon or Tuesday.

[peteski]

Sounds like you solved your problem Pete!  Good job.  I just want to chime in on mixing small quantities of resin.  All of my resin castings have been so far miniscule. N scale golf carts or dodge-em cars, or items even smaller (like street lamp bases or finials).

So I only mix very small quantities of resin each time (I end up tossing about 90% of even the Smooth-On trial size kits because the resin goes bad before I have a chance to use it - even when using their gas-blanket).  Anyways, when I make the rubber molds, I mix the rubber in one of those 1oz medicine measuring cups.  Since my molds are also small, I usually have plenty of mixed RTV left in the cup. I spread it all the way  up the walls of the cup then let it harden in the cup. Then I remove what looks like a RTV mold of a medicine cup.

I use that soft cup for mixing my resin.  My resin is stored in 10 plastic paint bottles (old Accu-Paint bottles with a yorker spout lids).  Then I dispense ans measure the A and B parts by counting drops. It takes few tries to come up with a proper proportion (since part A and B are different viscosity, so the drops are not equal in volume), but since I mix it in those soft RTV cup, it is easily cleaned out.  In the end, I end up with a proportion of let's say 10 drops of A and 13 drops of B. I mix it in the rubber cup using a rounded Popsicle stick, then I often use a toothpick to "pour" drops of the the resin into my 1-piece open molds.  Whatever resin is leftover I let it harden in the rubber cup. I can then easily remove it and mix another batch.  I also first coat the wooden Popsicle stick and toothpick with epoxy to seal them and prevent them from absorbing moisture which could cause bubbles in the resin.  Once I'm done pouring a batch, I clean them with a piece of a paper towel to make them ready for next use.

[pnolan48]

Very innovative way to do mixes, Pete!

I am at the very opposite end when it comes to quantities. Some of my molds required more than a liter (quart+) of silicon. I use 11 oz and 18 oz cups. I pour 7 oz of each component into the 11 oz cups--that is to the top of the ribs in most designs. It may take two or three sets of cups. I mix the 14 oz of A & B in the 18 oz cup and begin to pour. Then I mix the second set of A & B into the same 18 oz cup and continue the pour. If I pour very slowly (and there is plenty of time) I can see most of the air bubbles pop while flowing out of the cup. Then onto the third set of A & B. In this way I am not trying to mix up a huge amount of A & B in a great big pot.

With large casting pours, I use a slow setting resin with the same method. With large pours, a slow setting mixture that should have a pot life of 30 minutes actually has a pot life of about seven or eight minutes, due to the heat generated by large volumes. Since many of my large molds are "sandwich squishes"--an interior plug fills up the central volume--I still have to work fast, so the plug more or less disperses the volume before the heat sets in.

I buy four gallons of casting resin (two fast, two slow) at a time, and never have much problem with aging. I buy two gallons of platinum silicon RTV (one each of A & B), and use a gas to displace air. As the RTV ages, I degas both components (although only B or the polymer is supposed to absorb moisture), not to remove air bubbles, but to remove moisture, much like pumping down an A/C system. I also add a little thinner once in a while. My latest batch of RTV was bought in January, and is now about 3/4 used. The remaining 1/4 is still very usable--but I am looking for a large project to use it up soon, before my winter in Alabama. Perhaps a 180' coastal freighter or container ship?

The problem with big batches is, of course, having a little bit around for the next small project! The vacuum pump helps there.

[DKS]

I've had just the same disaster; I thought I'd ruined about 8-10 molds with a gooey mess. I soaked the molds in 91% alcohol overnight, and after some careful poking with some cotton swabs and more alcohol rinses, I recovered the molds. Incidentally, I regularly mix <1.0 oz of resin (that's <0.5 oz of each part). Disposable pipettes allow me to reliably mix only as much as I need. Ironically, I buy several gallons of resin at a time, as I will often fill dozens of molds a day.

[pnolan48]

I've been afraid that 91% alcohol would affect the molds.

[peteski]

I've been afraid that 91% alcohol would affect the molds.

In my experience isopropyl alcohol does not negatively affect Silicone RTV molds, but using naphtha swells them quite a bit  (they eventually return to original size once the naphtha evaporates).

[Sokramiketes]

I wipe out the excess and then just pour in properly mixed resin again.  It'll cure the remaining residue... though you will probably toss the part.

[DKS]

I've been afraid that 91% alcohol would affect the molds.

The molds in question are still in use, better than two years after the accident.

I wipe out the excess and then just pour in properly mixed resin again.  It'll cure the remaining residue... though you will probably toss the part.

Tried that--because of the size and shape of the cavities, simple wiping was not enough, and fresh resin refused to cure itself, let alone the residue in the mold. The alcohol helped dissolve the uncured resin so it could be flushed out.

[briggsmodels]

I can assure you alcohol won't harm your molds. Use 99% tho. I often clean the molds with it to ensure there's no contamination. Use a swab and the alcohol to clean the oops out. Best way.

[pnolan48]

As David found, sacrificial pours will not only not clean out the residue, but cause another mess when the new pours don't harden themselves. Also, the sacrificial pours, where they do harden, will be stickier than usual, posing more threats of tearing. I know this because I tried three pours thinking as Mike did. Best to just wipe as much away as possible, using toothpicks (manicure sticks are better) to scoop away material in the crevices.

I got everything clean and working. I lost one of the four container "bays" in the mold, due to the sticky stuff tearing out two air bubble size holes in the roof. I suppose I could just cut the bumps off every cast from that bay, but they'll just get larger. I have started to repair some of my larger molds (mold material does stick pretty well to mold material), but I'll pass on this.

[Sokramiketes]

As David found, sacrificial pours will not only not clean out the residue, but cause another mess when the new pours don't harden themselves. Also, the sacrificial pours, where they do harden, will be stickier than usual, posing more threats of tearing. I know this because I tried three pours thinking as Mike did. Best to just wipe as much away as possible, using toothpicks (manicure sticks are better) to scoop away material in the crevices.

I got everything clean and working. I lost one of the four container "bays" in the mold, due to the sticky stuff tearing out two air bubble size holes in the roof. I suppose I could just cut the bumps off every cast from that bay, but they'll just get larger. I have started to repair some of my larger molds (mold material does stick pretty well to mold material), but I'll pass on this.

Interesting.  I haven't messed up a pour since switching to Smoothcast products, but swear I pulled a sticky residue off this way with Alumilite... it just left the sacrificial casting with a softer surface than normal.

Maybe mine was more of a missed ratio of resin and catalyst, and this scenario is of non-curable mess is from not shaking the bottles before pouring each part?

[DKS]

...didn't mix the two very well before pouring into the molds.

This is exactly what I had done, so there was all manner of different proportions of partially or unmixed resin--plus three color dyes--in each mold, and I was convinced I'd ruined them. But several cycles of alcohol soaking, wiping and rinsing finally brought them back to life. Took hours to clean up the mess.