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Pressure casting urethane

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Hi, can anyone help me out with this recurring issue i get with bubbles under the surface of  resin lures. The explain further this is my method of casting my bodies   


Check humidity is below 40 before starting 

the resin is stored correctly 

mix a and b resin together in exact amounts 9 min pot life resin

add micro bubbles upto 10%

mix thoroughly 

vacuum degass the mix for 2 mins

pour carefully into the mold (vented)

place in pressure pot at 60psi for 2 hours. 



Once the blanks are set i sand off the sprues and usually notice a few black spots which are bubbles beneath the skin. I can drill them and fill but it takes time. Everything i read indicates that pressure will take care of all the bubbles but yet it doesn't seem to work in my case. 


Any help would be greatly appeeciated. 



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The only thing I can think of is that you are taking too much time to get it poured and under pressure.  The humidity should not matter at all.  Adding MB to the mix can thicken it and speed up the cure a little, but not that much. 

My suggestion is to get it into the mold quicker and to get it into the pressure pot faster.

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Sometimes it is tough to be sure of the problem.  I have never had your problem so I don't know if it is a problem with a specific product, a technique, etc.

If you can send me a close up picture of the issue I might be able to answer your question.  Maybe. 

Your description of what you are doing seems excellent.  I would not even bother to degas first if using pressure casting so you are doing more then I would.

Sometimes the devil is in the details so the solution could take some time.  Please include a picture of the black spots or PM me and I will help the best I can.

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Hi guys. Im new to this forum. Builder from the netherlands. 

To reply on the question, my experience with the problem is that when the 2k urethane is old ( more than 2 weeks after opening new bottles) more air is produce when the blank is cured. Thats why I always buy small packages and pour a freshly openened bottle as fast as possible. 

Hope this will help you solving this problem. 

Best regards, Armatus

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The bubbles under the skin are more an likely from the microballoons..   It can also be from the age of the resin as aramatus explained.  If you open up a fresh can and you still get the bubbles under the skin it's the balloons.. 

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