Smooth cast 321 many bubbles

[juntari]

Hi, I'm working on a project and I'm getting mixed results with a material, would like some advice if possible.

I'm slush casting a helmet with smooth cast 321. While I'm working with it everything seems fine and goes everywhere smoothly but as soon as it begins to get milky little bubbles pop up in it. And not just a few bubbles, but the whole thing turns into an aero bar. I tried thin layers, thick, I get the same results. I'm thinking that as it gels and rolls around slower it picks up air which doesn't have a chance to escape. I'd like to stop slushing it before it gels but then it just gathers at the bottom. I'm trying to build up as many small layers as I can but I'm afraid that all the air is going to make it weak and prone to snapping off. Any suggestions? I tried a layer mixed with ure-fil3, it worked out great but I wanted a layer without it for the final one to get a smooth finish inside.

On a side note, I've used smooth cast 300 before with no problems. I wanted to get a material that doesn't set as fast to avoid lumps, so if anyone can shine a light on what I might be doing wrong it would be greatly appreciated.

 

[exoray]

Moisture contamination... Not all resins act the same, some are tolerant of moisture other erupt like a volcano in it's presence...

Do your casting on a less humid day, if that doesn't work it's the resin itself that is contaminated... You will need to either vacuum boil the moisture out of the two halves of resin or traditionally boil it out using a hotplate... Don't mix the resin, boil the individual halves separately straight out of the container... Do the hotplate boiling OUTSIDE if you have to do it this way and don't just crank it up to full, bring it up to a slow simmer and let it go... And don't use the same pot for both halves unless you clean it VERY well... I vacuum boil for about 30 minutes under constant draw when I do it, remember it will increase in volume substantially under vacuum so use a much larger container... If you do the hotplate obviously let it cool back to room temp before using or else you will have no pot time

Consider using a blanket gas in your resin bottles to prevent further moisture contamination... I use Argon, out of a big welding tank, but you can get little spray bottle of Nitrogen or other blanket gas mixtures at most casting supply places and even fine wine liquor stores as it's use to blanket opened bottles of wine to preserve them...

 

[OdiWan72]

What´s already been said...moisture!

I´m using Smooth Cast resins for quite a time now and while they usually bring good results, they´re pretty sensitive to moisture.

Happens mostly with slow setting resin OR when you use contaminated "fillers" like a wooden core within a bigger cast. -> Bubbles like foam then :unsure

Markus

 

[Snow Builder]

Also, I think the materials you use in your buck can cause a reaction. Be careful what primer, paint and/or clear coat you're using.

 

[exoray]

Happens mostly with slow setting resin OR when you use contaminated "fillers" like a wooden core within a bigger cast. -> Bubbles like foam then :unsure

Not if you seal the wood first...

 

[OdiWan72]

Not if you seal the wood first...

Smarta** :lol

I had this problem when I did a few casts of my STGW44.
I used a slow setting resin AND put a wooden dowel in the mold for added strength and support (ran out of aluminium tubing).

Did this once with "foamy" result and blamed the weather,
did this twice with "foamy" result and blamed the resin,
did this a third time with "foamy" result and finally realised what and WHO to blame

Markus

 

[Yodajammies]

10 points to griffynd- er, Exoray.

I came to post exactly that -

Moisture contamination... Not all resins act the same, some are tolerant of moisture other erupt like a volcano in it's presence...

 

[Jive Turkey]

Resurrecting this thread with a question. I bought a pint kit of Smooth Cast 321 today to cast a tiny head i molded a couple weeks back. The entire volume of the cast was maybe a shot glass size. But as it cured, I noticed some foaming from the pour spout. When I demolded an hour later, there were dozens of tiny bubbles just below the surface of the cast, virtually throughout the entire thing. I found this thread today and it sounds like I'm also dealing with moisture contamination. But I literally opened the bottles minutes before pouring into the mold. It might be mildly humid inside, but is the resin so finicky to be affected in such a short time? I used wooden tongue depressors to stir. Since the overall volume was so small, could even the wooden stir sticks introduce enough moisture to be the culprit? Could it just be a bad batch of resin? I'm going to try another cast tomorrow, but thought I'd try to narrow it down in the meantime.