Problems using Smoothcast 305 resin. Help.

GuntahKela

Sr Member
It's my first time using this resin, and it's frustrating. I will call Smooth on, tomorrow, for tech support, but I want to see if I can find the problem tonight.

I ordered smoothcast 305 because of its slower curing. I'm casting a thick item, and I want to avoid the heat reaction over multiple resin mixes. Well, the first casting was a disaster: Warping, blistering, weeping and lost of liquid resin on the surface, after curing.

No matter how little of it I mix and pour in the mold, the resin still blisters and leaves liquid resin over the cured surface. Yes, I'm mixing properly, equal parts. What could be going on?
 

OdiWan72

Master Member
RPF PREMIUM MEMBER
What is your mold made from?
Do you use clean/ dry buckets for mixing the resin?
Do you use a plastic or dry wooden stirrer?
Do you use some kind of filler for the mold?
What about air humidity?

Sounds like you´re contaminating your resin with humidity at some point, causing the blistering/ uneven curing? I had the same effect with fast kicking SmoothCast, when I tried to insert a wooden dowel into a STGW44 mold for added strength&support. The wood, while dry to the touch, contained enough humidity to make a mess out of my cast (THREE times, before I realized what was going on :lol) Similar thing happened to my first casts with slow setting resin on another project...too much air humidity-> blistering :unsure

Markus
 

robstyle

Master Member
by some odd chance are you using a mold release and what Markus said, what type of material is the mold made from?
 

GuntahKela

Sr Member
What is your mold made from?
Do you use clean/ dry buckets for mixing the resin?
Do you use a plastic or dry wooden stirrer?
Do you use some kind of filler for the mold?
What about air humidity?
-Mold is made off smooth-on Reflex 40 urethane.
-Yes, always use new and clean cups to mix my resins.
-I stir with my finger (wearing disposable nitrile gloves) for a minute, or so.
-No fillers
-Humidity could be a factor. We have had sudden weather change in South Florida. It's cloudy and rainy, for the last few weeks, and humidity is at a 92%. Casting for 10 years, never seen weather being an issue, only for painting. It's also my first time using 305, so what would I know.
-Yes, I use Smooth-on universal mold release. I must, or the resin will get stuck to the Urethane molds.

Thanks, guys.
 

modelnutz

Member
Sounds to me like your resin has been sitting for a while....most likely the 'A' side has seperated. That's what's causing the poor cure and wet surfaces.

The solution... heat the resin ( in a low temp oven ) and mix the seperate parts very, very well before casting again.

You might also need to check and see if you are using too much mold release...you should be spraying on a coat, brushing it in, wait 15 min. , then follow up with a light coat....let the final coat dry for 10 to 15 min.
 

Finhead

Sr Member
-Mold is made off smooth-on Reflex 40 urethane.
-I stir with my finger (wearing disposable nitrile gloves) for a minute, or so.


Thanks, guys.
What? Use a stir stick and scrape the sides as you stir you really need to mix it well or the part that isn't mixed in will sweat out of the cured (properly mixed) resin. Also along the same lines as modelnutz sounds like your A is separating. I've had this before what I do is shake the hell out of both parts a few hours before or first thing in the morning i I'm going to be using resin that day. This will mix it well and allow some time for the bubbles to dissipate.
 

GuntahKela

Sr Member
Hmm, I've been finger-mixing smoothcast 300 for the past 6 years without any problems, side-scraping and all, but I'm willing to try a mixing stick for the 305 issue. I've have been shaking the bottles, but I guess I can give them a harder-longer, upside-down shake.

How do you recommend I put the part A on the oven? should I pour it all in a metal pot and just place it inside? Any temperature recommendation? Bake? Broil?
 
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