High Strength 3 + BassinK9 = EPIC FAIL!

[BassinK9]

Larry/Mike:

Bought some HS3 to make a new mold for making "umbrella" rigs because I've been selling a few to friends and coworkers.... wanted to make a 3 headed version and everything seemed to go well until it came to unboxing my mold. I poured three "dummy" heads using Alumilite regular and dangled them from a wire to make my cavities. After 24 hours, I deboxed my mold and tried to pull the heads out..... and they didn't want to let go. It turns out all three cavities are useless (unless bass like shad with chronic acne) with "pock marks" from where the silicone didn't want to release.

What did I do wrong? I measured carefully and poured all the silicone in one spot to avoid bubbles.... and even let it cure longer. Should I have coated the dummy heads with something? Help!

[dahlberg]

What were the heads made of? Could be either the material was too porous, or had moisture in it. If using skulpy I like to hit it with a light layer of permalac or other super fast drying surface coat to give it a slick finish.
Maybe Mike will weigh in with an opinion, but that's my best guess.
best

[BassinK9]

Larry:

I poured the heads out of Alumilite Regular and tried to be careful not to handle them...... talked with Carol yesterday and she felt that perhaps atmospheric conditions had something to do with it. Although I poured the mold in my kitchen, it had been raining for a couple of days so possibly the humidity could have been the problem. In any case, I shouldn't have tried to demold the heads when it became apparent they didn't want to let go. Letting the mold sit for another 10-12 hours might have saved me the trouble because the next morning, the mold felt much less tacky to the touch. I just suspect that the high humidity slowed the curing process somewhat.

I'd love to hear Mike's input on this as well....

K9

[dahlberg]

My guess is there was some condensation on the heads. Just last week, in a huge hurry, I put the first half of a mold in the sauna with me. I tossed a bucket of water on the rocks before leaving the sauna and a few drops splashed on the mold. After an hour I took the mold out, blew it off with an air compressor, wiped it so if felt dry etc. I then hit it with UMR, like 4 times, and poured the second half. It took forever to set up and had some trouble getting it apart. I've been working with this stuff for years and this was my first experience with micro amounts of water in my mold goop and I will not make that mistake again. Although, the sauna and high humidity usually make the material set up really fast and really firm!
best
L

[Mike - Alumilite]

Wondering, did you use any mold release in the mold when you poured the Alumilite Regular you used to make your mold? Sometimes, you get mold release transfer that hangs on your part and that mold release (if silicone base ... like Stoner), will act as a primer for the silicone rubber to bond to. If you do use a mold release when pouring originals ... make sure to wip them down with alcohol or some mild solvent to remove any mold release transfer.

If you have UMR mold release, you can always spray it on your original to be safe but is absolutely required to coat heavily when making two piece molds. The tear strength on the High Strength 2 and 3 are so high that even minimal porosity, surface tension, or bonding for any reason really can make demolding difficult.

If the material is not fully cured and crosslinked, the rubber may also feel a little more "spongy" and you will be much more apt to tear the mold when demolding. If ever in question, allow it to cure longer and then take great care when demolding. If surface tension is high between the mold and the original, squirt some rubbing alcohol inbetween the two and slowly work it until it separately. The downside of using the alcohol is that it may affect the paint you have on your original.

There are often so many factors, it is tough to pin point individual circumstances on a particular mold, but hopefully some of this info gives you some insight and helpful info.

Mike
Alumilite

[BassinK9]

Thanks, Mike.... I never use any type of release agent so that shouldn't be a factor, but I agree, when I try this again, I will simply wait it out if the pieces don't want to de-mold.