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ark50000

Sealant For Pop Molds

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I have made my plaster of Paris molds and they turned out great. I am now in the process of making a two part injector mold. The only issue i am having is after i have poured the plastic, bubbles start to seep through the plaster mold. I know its not the plastic itself but rather the plaster mold. What should i use to seal it properly? I have tried five coats of clear nail polish and a gloss spray paint enamel. Neither have worked 100%. Both worked slightly but wore off quick. Should i maybe try Mod Podge? what do you recommend. Thank you !

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2 most used are epoxy thinned with denatured alcohol, or elmers wood glue thinned with water

I started using both (epoxy over the wood glue) and havnt had any problems yet

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I used Epoxy I bought at Home Depot. I thinned it out with denatured alcohol. Be careful it doesn't puddle on you when it is drying. The puddle will fill in ridges of a mold and you will lose the detail of the worm. Any alcohol spilled on rags went outside immediately- highly flammable. For aluminum molds I used high temp epoxy paint (500 degrees) bought at Walmart in the automotive section. The paint worked great and made the baits more glossy looking. I will be trying the paint on my Plaster molds someday.

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I use Mod Podge it works great.Never had to redo a mold. Just watch how you put it on. If you use a paint brush, you can get brush lines in the bait. I put on three coats

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I used 3 or 4 coats clear gloss spray in a can.. Let dry and go over it with 2 or 3 coats clear nail polish... Works good for me. I reseal with nail polish every 8 or 10 pours..

 

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Elmers Wood Glue thinned with water works great with one coat.  Mix 50/50, flood cavities, let sit a few minutes, brush out cavities with foam brush, brush onto rest of mold, bake at 150 until cured. Simple, easy, durable.

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I don't know about Gorilla glue. I tried a different brand from Lowes once ( Don't remember the brand. ) and the finish was dull and rough. Stuck with Elmers after that. Elmers is cheap, and gives a great finish every time with a single coat. 

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Be sure your POP is completely dry before you seal it with a glue/water mix, or you can get mold under the sealer, which will eventually fail.  Don't ask me how I know, but I am going to have to redo my rage craw mold next week!  The half sealed with diluted epoxy is fine, but I have to do both halves again, because I can't get the soft plastic masters to go back into the epoxy sealed side.  Grrr!!!  Hahaha

 

Edited by mark poulson

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Good advice Mark. Fully cured/dried molds is extremely important. I pop mine in the oven at 150 for several hours with the door cracked open a wee bit to dry them.

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I weigh my plaster molds on a gram scale. When the mold stops losing weight in the drying process then the mold is 'dry'. From personal experimentation; PoP loses weight at a constant rate, there is no gradual slowing down of the weight loss, so it is very easy to determine the dry point.

I mention this because over drying in the oven can make the mold powdery. A cracked open oven works well, but the ideal rapid method is a warm box with fan circulation. I used 3x 100W incandescent (filament) bulbs as the heat source. If you make a lot of molds, this simple wood construction oven is worth building.

Dave

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On 3/17/2019 at 8:37 AM, Vodkaman said:

I weigh my plaster molds on a gram scale. When the mold stops losing weight in the drying process then the mold is 'dry'. From personal experimentation; PoP loses weight at a constant rate, there is no gradual slowing down of the weight loss, so it is very easy to determine the dry point.

I mention this because over drying in the oven can make the mold powdery. A cracked open oven works well, but the ideal rapid method is a warm box with fan circulation. I used 3x 100W incandescent (filament) bulbs as the heat source. If you make a lot of molds, this simple wood construction oven is worth building.

Dave

can you share more info on this? maybe a photo?

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Here is an isometric and a section through my simple pop dryer. the light blue shelf lifts out. PoP molds can be placed at the bottom of the box and on the shelf.

If you do a lot of molds, you could build a cabinet with lots of shelves. The holes above the fan is low pressure (fan blowing down) and so draws fresh air into the box. The holes below the fan are high pressure, so blow out wet air. Thus, moisture never builds up, maximizing the drying effect.

pop dryer 2.JPG

pop dryer 1.JPG

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Here is a spreadsheet of the drying times. This was never intended for publication and so is a bit rough. But, it does give an indication of the drying process.

Contrary to what I remember; the rate of drying is not constant, but it tails off significantly at the end. You do not need 100% dry. Once the loss rate drops the mold is dry enough to use.

The molds sit on dowels so airflow reaches all surfaces.

Dave

pop dryer 3.JPG

Edited by Vodkaman

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17 hours ago, Vodkaman said:

Here is an isometric and a section through my simple pop dryer. the light blue shelf lifts out. PoP molds can be placed at the bottom of the box and on the shelf.

If you do a lot of molds, you could build a cabinet with lots of shelves. The holes above the fan is low pressure (fan blowing down) and so draws fresh air into the box. The holes below the fan are high pressure, so blow out wet air. Thus, moisture never builds up, maximizing the drying effect.

 

  

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As Dave suggestions highlight in his diagram.... AIR MOVEMENT is key to drying and drying fast - heat helps - but if you trap in the moisture (ie. oven with door shut) you're just basically creating a sauna which doesn't really dry very well.  I've had good sucess just laying molds on a window sill that gets alot of sun and having a small cheapy fan blow over it... actually worked better than my small electric oven with the door cracked open.

Edited by SlowFISH

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SlowFISH is spot on, it is all about air movement. If I run my box without the lamps the drying time doubles, but to achieve this level of drying just by placing in a room would take a week or more. Another good place is on top of the refrigerator were there is air movement which reduces drying time to 3 - 4 days.

After all the testing I built a simple moisture sensor which beeps (very low volume) at different speeds depending on moisture, continuously once dry. So, no more weighing :)

Dave

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