Diaster with Scale Molds

[jazz2453]

Hello, so I made two molds and they came out awful. That's just the maid idea but here's the whole story:
I was working on the scale sheet model using sports ball foam circle stickers. It came out great, the scales were perfectly fine and looked good. Here I am making the model:
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So, then it came down to molding. We prepped the mold very well, applying the correct sealer and release. We used Shell shock backed with plastipaste to make the mold. We de-molded to find all the foam circles stuck in the mold. No worry, we can just pull them out. That's what we thought... Most came out, but many pieces were stuck under little things of shell shock. We tried for weeks to do everything we could, including using a chemical to dissolve the foam. WELL, it ending up making tiny cracks in the mold. With the foam stuck, and all these cracks, we decided that it was trash. Here's the mold ( it was in the sun for awhile so it turned yellowish).
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So ASAP we ordered different circles and began take 2! This time we ordered foam math counters and they were really thick and looked AMAZING! I was so happy and made sure we did nothing wrong for this mold. Here is the scale model:

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Cool, right? We even made a youtube video beginning how to make the scales: YOUTUBE VIDEO (https://www.youtube.com/watch?annotation_id=annotation_2629163183&feature=iv&src_vid=YnQxrO7edDY&v=LRFWcv6ksq0)
Just today, we used glue to seal the scales, then applied tons of vaseline for release. We even recorded it to make the second part of the video. Then we began making the mold, this time using fiberglass. We made sure we did everything perfect, we made everything neat, we were going to do 2 layers, the second layer including cloth for extra stability. After pouring the material on the scales, we took a break. We came back 20 minutes later to check on it, and this is what we found:

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YAY! All of our hard work and dedication right in the trash! I was devastated, crying. I have orders and needed these molds to finish the tails but instead I get this!
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We probably spent over 50 hours working on these scale sheets (much of other setbacks not even included in the story). We worked so hard and we don't even know what we did wrong. UGHHH!

Can you guys help, do you know what could've gone wrong?

[Mermaid Fenicia]

no links to the pics :(

[jazz2453]

Oops, let me fix that.

[BayouMermaid]

I can't see pictures, so I don't know if we had the same problem. Could you repost them please?

I did a similar process to yours and also had a disaster. Foam circles sealed with glue and coated with vaseline for the positive and fiberglass resin to make the mold. Mistakes that I made according to my dad who has built fiberglass boats before:

Mistake #1. Not using gelcoat. According to my dad, the gelcoat is applied very thinly, preferably sprayed on, and it helps protect the positive and provide a base for the rest of the resin.
Mistake #2. Pouring resin too thick. I should have brushed it on so that it didn't get too hot.
Mistake #3. Using too much MEKP (hardener). The resin kicked too hard making it heat up too fast.
Mistake #4. Not waiting for each batch of resin to harden before applying more layers. This caused the layers to harden unevenly and warp.

My mistakes caused my mold to smoke and warp terribly to the point that I had to throw it away. I am currently waiting for good weather to try again. I understand the pain. I also cried for several hours, so don't feel bad.

[BayouMermaid]

Ok, I can see them now. I will say that my foam scales did not stick to the resin. I put down tons of vaseline and used a hairdryer to melt it so that it was smooth, then allowed it to resolidify at room temperature. My dad suggested using mold release wax instead of vaseline.

[jazz2453]

I did exactly want you did. Tons of vaseline, brushed it out, then melted it with my hair dryer. The foam wasn't actually stuck to the resin, they came out easily. The top part of them wasn't covered, so they were stuck because a piece of them was in a hole in the fiberglass. If that makes sense? It's shown in the last picture.

[BayouMermaid]

Some info from this site: http://www.sculpture.net/community/showthread.php?t=1887


Another idea would be not to cast the piece solid. If it's large enough to do a gel coat and then laminate with fiberglass, you will have much less heat, thus much less shrinkage/distortion. If the castings are small then another option is to manually rotocast the pieces hollow. Pour in just enough resin to coat a thin layer, close up the mold and then roll the piece around to get the resin evenly distributed. Pour back out any excess resin during the rotation, and keep rolling till the resin kicks and fully sets up. Check this by watching through the mold openning or watching the left over resin in the mixing cup. You can rotocast in subsequent layers to build up enough thickness for strength. these layers can also be thickened to honey like consistency with filler and still work well in rotocasting. Just make sure to evenly distribute the resin so no thick areas produce heat enough to distort.

Last, I found that urethane resins don't shrink or distort near as much as polyester, though I would only recommend their use in an outdoor casting set up as no respirator is certified for them.

What I think happened is that the mold started to shrink on both sides (perhaps due to heat) and caused the hole to form. I've been trying to learn more about how to fix my mistakes, so hopefully this will help you too.

[BayouMermaid]

By the way, that info is about rotocasting in sculpture, but the basic information should still apply to our situations.

[Coradion]

So, I had the same problem with shell shock when I made my first fin. Shell shock is actually super sensitive to temperature and I wasted a lot of shell shock learning to mix it. Sometimes it's better to adjust the ratio of the part from the metal can and use a bit more. Also there's like chunky chalky crud on the bottom of the bucket you have to make sure you get that part mixed into the rest of it before you mix the two parts together. Literally take a hard stick and pry it from the bottom of the bucket. Be really thorough. Make sure you got all the bubbles out with compressed air, any bubbles lead to cracking with some chemical solvents and temperature.

For the fiberglass it probably got too hot and melted parts of the foam contracting and pulling it with shrinkage. Foam isn't really the best material to use with heated plastics. Also vaseline can disrupt some chemical cures, petroleums are sometimes reactive with other plastics decreasing their bonding ability and cure. I would try again, but maybe with clay?

[PearlieMae]

Oil based clay has served me well, along with Smooth On's 325 Resin. It heats up, but not crazy hot like fiberglass.

Before you try to cast a huge sheet, perhaps try a small test?

[Mermaid Harmony]

I feel way underskilled to actually help in some way other than to express my sorrow for you and your molds, they looked beautiful.

[Anahita]

Oh man, Jazz, that sucks so bad. :(

[Morticia Mermaid]

Not sure which is worse, having a scale mold not work out, or a fluke mold not work out :/

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[Coradion]

Not sure which is worse, having a scale mold not work out, or a fluke mold not work out :/

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Both suck a lot. Scale molds take longer but fin molds take so much more time and it's something you shape and create.

[Mermaid Miel]

ZenHugz Jazz.

Every starting Tail-maker comes across setbacks like yours.
I know that when you are finished that the tails you make will be even more awesome for the wait!
After all, every setback is just an opportunity to learn more and do it better the next time around.

[jazz2453]

Thank you Miel:) you're very kind!