What causes resin "beads"?

bob242 · Post by **bob242** » Thu Dec 07, 2006 2:48 pm

Not sure of the term, but I just got a model that has little balls all along the edges of the detail. They don't really feel attached in most cases as they just pop right off. Curious as to what causes this.

DX-SFX · Post by **DX-SFX** » Thu Dec 07, 2006 3:10 pm

Air bubbles in the surface of the rubber mould getting filled with resin.

Darkov · Post by **Darkov** » Thu Dec 07, 2006 3:38 pm

Yep airbubbles in the mold causes them. They tend to show up more if you pressure cast. And mostly along a seam or on a sharp edge.

bob242 · Post by **bob242** » Thu Dec 07, 2006 3:48 pm

Pain in the butt, they are. Does this reflect on the caster or is it just something unavoidable? We're talking about 75+ on a 14" piece.

Darkov · Post by **Darkov** » Thu Dec 07, 2006 4:06 pm

Sometimes they are unavoidable.....but form what you describe it sounds like they needed to de-air the rubber before pouring the mold.

Sparky · Post by **Sparky** » Thu Dec 07, 2006 5:04 pm

I saw these between a cuff and the leg/hand, it might mean they deaired the RTV then poured it on the mold, that narrow tight passage will tend to trap air ubbles in there as the RV attemps to flow in.

You have to deair the RTV/master after pouring the RTV. Brushing on a layer of RTV is probably more time consuming and error prone than just throwing the mold box/master/rtv into the pot and dearing it once more beofre setting it aside to cure.

DX-SFX · Post by **DX-SFX** » Thu Dec 07, 2006 6:25 pm

You don't necessarily need degassing chambers or pressure chambers if you brush the pattern with rubber first and then let this initial coat partially cure. This will fill any detail that would otherwise trap air. Repeat if necessary although you rarely need to. Then mix up some more rubber and pour normally. If you use a slow set rubber, i.e. a 24 hour cure rubber rather than a 1 hour cure rubber, it gives more time for any bubbles to rise to the surface. It takes a little longer as Sparky mentioned but it's worth it.

Sparky · Post by **Sparky** » Fri Dec 08, 2006 12:22 pm

DX-SFX wrote:You don't necessarily need degassing chambers or pressure chambers if you brush the pattern with rubber first and then let this initial coat partially cure. This will fill any detail that would otherwise trap air. Repeat if necessary although you rarely need to. Then mix up some more rubber and pour normally. If you use a slow set rubber, i.e. a 24 hour cure rubber rather than a 1 hour cure rubber, it gives more time for any bubbles to rise to the surface. It takes a little longer as Sparky mentioned but it's worth it.

go with the mold max 30, it seems like its tricky to mix (mix by weight) but I used a chefmate food scale from target for my trial pack and it works fine (max wieght it can weigh out is limited though). This stuff is much more watery when mixed and has a longer setup time.

Blappy · Post by **Blappy** » Mon Jan 01, 2007 11:17 pm

Sparky wrote:
You have to deair the RTV/master after pouring the RTV. Brushing on a layer of RTV is probably more time consuming and error prone than just throwing the mold box/master/rtv into the pot and dearing it once more beofre setting it aside to cure.

Careful though. I degassed a master in rubber once and the maste actually ruptured under the vacuum. I had to destroy the mold and cause more damage ot th master to get it out. I use a little dental tool to make sure the rubber gets into the narrow spots after pouring on a very thin layer.

Blappy · Post by **Blappy** » Mon Jan 01, 2007 11:22 pm

Sparky wrote:
go with the mold max 30, it seems like its tricky to mix (mix by weight) but I used a chefmate food scale from target for my trial pack and it works fine (max wieght it can weigh out is limited though). This stuff is much more watery when mixed and has a longer setup time.

I mix my MoldMax-30 by weight and have no trouble.

I just add a little extra catalyst volume wise to compansate for the different densities.