Resin Failed to Cure?

[vader1974]

Has anyone ever had issues with resin not curing properly?

I was using Smooth-on 321 casting resin.

The first batch of castings was outstanding, but the second batch failed to cure (even after 12 hours). Hopefully the molds are not ruined, I am in the process of cleaning them up today.

The end result was a thin layer of cured resin directly against the mold and a jelly of uncured resin filling the rest of the cast.

The only difference between the first batch and second was a huge rainstorm which increased the humidity on the garage greatly. Could this be the problem?

The resin was brand new and opened just prior to the first cast.

Thanks
Brian

 

[Jedirick]

If the containers were resealed, I doubt humidity had much to do with it unless it was several weeks between pours. I've poured in 50 degree weather and not experienced a problem except for a delayed kick if the mold is cold as well.

If you think you will not use the entire gallon kit in the next few weeks I'd recommenf going by a wine specialty shop and getting a can of spray blanketing gas. A shot in the jug prior to resealing can double the life of your resin.

I have experienced partial cures with Smooth-on before. Their 300 and 300 Q series kick time is 1-3 minutes and never seem to have a problem. I believe the 321 is about 7-8 minutes kick time.

Sadly I have found out that the problem is not the resin but me.

The slower the pot time the more you need to make certain that A/B jugs are well mixed in the jugs prior to dispensing measured amounts. Slower the kick, the higher the chance of seperating of ingredients in the kicker.

Uncured resin in molds sucks. Sometimes you can add some additional kicker to the uncured resin and it will kick or at least solidify the mess some more. I have found rubbing alcohol sometimes help clean stickyness from the mold and warmwater and Joy dish detergent are helpful without drying release lubricants in the silicon. Once clean, you may want to apply a release to mold for your next pour.

Someone recommended freezing the mold and uncured resin for a few days and then supposedly it is easier to clean....I've never tried that but desperation can make you try most anything someone suggests.

 

[LeMarchand]

Have had the problem myself. And there are a couple of reason this can happen.

-Since it is new resin, i doubt the resin has been affected by humidity yet, it can be a factor when you leave both parts alone for some time in their closed containers without a gasblanket on top of it, the air in the bottle will otherwise affect the resin. I use 'x-tend it' gascans which i spray in the containers after use. The gas will drive out the oxygen and put a gasblanket on top of the resin so it will remain fresh longer.

-Did you stir/shacke both bottles of part A and B before you poured it in the cup/pot you where mixing it in? You really need to do this, or the resin will not cure and result in the same problem you are describing. When you leave part A and B for a while in their containers, you can seen that part B seperates into 2 different layers. If both containers arend stirred/shaken properly before mixing, you will have trouble.

-Store and use your resin at roomtemperature, cold weather will affect curing.

-last thing i can think of is if the mixing ratio was off.

hope this helps,

Marc

 

[LeMarchand]

heh, jedirick was able to type faster than me

I had the uncired resin problem 2 days ago (my faultm didn't stir part B enough). When the resin didn't start curing in an hour (i was using Smooth on 210) i knew i was in trouble.

I don't know if it will be a solution, but it saved my mold:

I poured as much uncured resin as i could out of the mold and opened it. Wearing rubber gloves i took out all the semicured bits and used paper towels to clean out as much of the resin as possible. I then put a load of talcum powder on top of the sticky resin stil in the mold and used a semi hard brush to brush out as much as possible. The i then used the end of the brush (the wooden pointy end) to carefully rub out the remaining bits. I then gave it a carefull but good wash with hot water and soap.It saved my mold, but i know that if i had waited longer, the uncured resin could have bonded to the silicone, especially when the mold was older and more dry.

cheers,

Marc

 

[vader1974]

Thanks for the tips.

Sounds like I did not shake up the bottles between the two batches. I have never used the 321 (longer to kick), and the quick stuff I have never had a problem after shaking the bottles at the beginning of a casting session.

Thanks
Brian

Update: User error. Unfortunately it cost me one of my three molds.

 

[uscm buzz]

yea I had this problem a few times recently.. realized I wasnt mixing parts a and b thouroghly.. ... exactly like you said it came out..