Two Part Pop Mold?

[Missinfish]

Working on a two piece POP mold, I usually use resin but wanted to try this. I have the first half poured and drying, do I need to seal the first half before pouring the second? So they don't stick together? Or is there another option?   Happy Holidays!

[mark poulson]

You need some kind of release agent so the second half's POP won't stick to the first.  

I use diluted D2T glue, two coats, to seal the face of the first half enough to make it semi-glossy, and then use spray PAM as a release agent.

I dry and cure my first half with the masters still in place, clean up around their edges as best I can to get a clean separation line, seal the first half with glue, and then spray the face with PAM.

Then I fill my second mold half tray with POP, brush some onto the masters in the first half with an artist's brush to insure that the POP fills all the little nooks and crannies,  and then lay the first half face down into the second half.  The excess POP will squeeze out the sides.

I clamp the halves together, turn them over so the wet half is on top, and tap and vibrate them so any air bubbles will move up and away from the masters and mating faces.

I've found that putting a little too much POP in the second half, as long as it's well mixed and kind of runny, is much better than not quite enough, which is a recipe for air bubbles and voids.

Take your time, and it will come out fine.

I brush glue onto the second half face, once it's dry, too, because POP is soft by itself.  The glue helps the molds to hold up a long time.

And I brush the glue into the mold cavities to make them slicker, which cuts down on air bubbles in the plastic baits.  Just be sure to dilute the glue with some denatured alcohol (DA), maybe 2 parts glue to one part DA, so it soaks in, and doesn't lose the details in the POP.  I make sure I've mixed the epoxy thoroughly before I add the DA.  Otherwise, the DA will bond to one half of the two part epoxy, and it will never set.

Good luck.

Edited December 25, 2012 by mark poulson

[Missinfish]

Thanks Mark, that was exactly what I needed to know.

[SlowFISH]

Many ways to attempt this.... if I am using a "hard pattern" that I can remove and reinsert into the mold easily, I pour first half, after it sets up for an hour or so (hard and starting to dry but not fully cured), I remove the part and clean the face of the mold up.... wet sanding it down just a bit if need be to get a nice flat face and clean parting line (just don't remove too much that you lock the pattern in on the second pour).  I'll then drill "domed" holes with a grinding bit to form alignment pins in the cavity.  I reseat the pattern and then use petroleum jelly as a release agent.  Smooth it all over paying attention to not fill in too much around the part... sometimes you have to use a pointed object to clear some out near the partline.  Then like Mark... I mix the second batch, first add some just near the pattern and brush it in places that may likely trap air, then pour enough in to cover the pattern and the shake/vibrate it real good to insure there are no bubbles next to the part.... after that I just add more plaster to fill the mold out and let it set.

 

  If you are using a soft pattern with alot fo detail/ribs (think ribbed swimbait or drop shot worm) I do not remove the pattern... it's near impossible to get it back into the mold after you remove it..... in this case I clean up as much as I can by hand and use the same process but never remove the pattern until both sides are made.

 

  Once the halves are done, I cure them at 100 degree in an oven.... this seems to evaporate most of the jelly, although I give them a good wipe to remove as much as possible before I cure them.  If they still feel greasy, I've "washed" a mold after it was dry with dish soap and water then dried it again..... didn't seem to efffect the mold.  After this I then seal (Elmers / DT or even used the water based DN a few times with decent results).

 

  Not the fastest process, but seems to work for me if I need plaster molds.

 

        J.

[robalo01]

Do you bake the mold closed or do you opene it to bake?

[ipt]

i bake mine in the toaster oven, face up split apart. 200 degrees for an hour or so, then let it air dry for a day

[Missinfish]

Thanks for all the input. The mold came out as well as I could expect for my first attempt. Learned a few things I would do different next time also.

I know have an issue with an air pocket forming in the bait and need to figure out if or how venting will fix this. I've been pouring the bottom half of the bait, letting it set about a minute then closing the mold and it pours from the end. The air pocket is about 2/3 of the way back on the bait. Not really sure where to go from here. I may try pouring it a few more ways before modifying the mold.

[ipt]

many tries and fails is how you learn! ive gone thru over 50lbs of pop and im still learning new things about making molds.

 

are you injecting or gravity pouring? send me a pic of the mold and ill take a look.