tiny pinholes in castings

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spitfire

spitfire

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Dec 22, 2007
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Location
bloomsburg,pa.
Once in a while when I turn one of my castings and apply the finish there are very small holes that are not noticeable until I apply my plastic polish. I'm sure a pressure pot would help avoid this problem, but what can I do the meantime to take care of the problem. I started to run my orbital sander on the workbench next to the casting and that seems to help the bubbles come out any other options?
 
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What family of resins are you using? Polyester or Polyeurethane?

Polyesters, you can vacuum de-gas, ultrasonic, and pressure cast. To reduce bubbles in your casting.

Polyeurethanes - I leave the answer for the experts in casting with that material.
 
I've noticed different brands trap more air than others.
I don't do anything special to reduce the bubbles and rarely get them without a PP.
Would you happen to be using Castin' Craft?
 
Sorry guess that would be helpful. I was using castin craft brand pr
I have some new stuff coming so maybe that will eliminate that. I know when I got it from Mr Fiberglass i did not have this problem now that I think about it.
 
I sometimes get pinholes in castings, especially when casting money. I just fill them with CA glue. Typically, I try to find and fill them after turning and before sanding. That keeps trapped dust from showing up later.

Regards,
Eric
 
Jason,

Dawn does not use pressure for casting the resin we sent you. I have never hit a bubble. It is not "Castin Craft", although we have used that brand in the past.

Hopefully, your next group will be "airless".
 
Typically when casting a product with lots of air pockets such as cactus, money, etc you have to use a pressure pot. I've just about stopped using it on solid color castings. On my snake and cactus castings I always pressure them to 45lbs pressure for 1 hour, after one hour I see no reason to keep them in the pot as by that time they have semi set and jelled to the state that no amount of pressure or time will force anymore air out. If I do run into a pin hole I will fill with CA before sanding, if you sand first you need to clean the blank with DNA before filling the pin hole to remove any sandind dust from the pin hole. I have also found that if the void is bigger than a pin hole CA will not "fill" it I use 5 min. clear eboxy to fill them.......
 
Jason,

IIRC, Castin' Craft is fairly viscous. As a result it will have a tendency to retain air bubbles longer. Anything that you can do to increase your open time (less MEPK) or reduce the thickness of the resin (pre warm) - or even some vibration will help! Also try to stir the resin gently when you mix in the coloring and catalyst. If you whip it, you will be adding in more air.

The new resin you will be getting will be thinner. Hopefully you will not have as many problems with fine bubbles. Please me know how you like it once you get a chance to play with it! :tongue::biggrin:
 
Dawn knows her goop!!!

But I turn her goop into pens. The resin is also more dense, when completely set. Not more difficult to turn, but different to turn. (Thicker???)
 
I agree, the Castin' Craft is much thicker and traps the air badly. That is why I asked if that was what he used and one of the reasons for me going to Silmar. Very rare to get bubbles now.
 
Ok an update. I am familiar with casting random items such as coffee bean etc. When doing those I used to use a pressure pot when I had one(sold it now I want it back LOL) and never ad any problems.

I never used a pressure pot when doing solid casting as I didn't see the need and never really had problems before but like I said back then I was using Mr Fiberglass resin.

The last few months I have been using Castin Craft and it makes sense to me now one of the problems is how thick that stuff is. I only realized this after last night when I got my new resin in (thanks Ed and Dawn!)

The new stuff is much thinner than castin craft and I could tell a difference in quality instantly. I should be turning one of the castings I did last night tonight so I will repoart back then.

Thanks for the help
Jason
 
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