Why is my resin sweating?


Sr Member
I've had this problem a few times now. I'm using Smooth On 305.

With the last batch, my first two pours were "sweaty". I threw one away but kept the other. After a few days, the piece seems all right.

I initially thought I was messing something up by shaking the containers (as per the instructions) and using it too soon. There's a froth that tends to go away after a few minutes.

Today, I shook the containers and waited 30 minutes before pouring. My first few pours were fine and then I got another sweaty piece.

I would have thought it was an error in my mixing but I stir everything at least 30 seconds.

Like I said, some pours are good and some aren't.

Any ideas?



Sr Member
how long did you leave the containers be after you shook them (so from shaking till the bad pour). My experience is that the slower the kick of the resin, the faster part 'B' seperates and needs to be shaken before mixing again.



Sr Member
Gone but not forgotten.
MANY factors can contribute to a " sweaty " part
after you take it out of the mold...

One, the Release Agent you are using will tend to build up
and create a barrier that " can " make a part sweaty after
a few pulls.. { IF your using a release agent ? }

Also, I have found that certain RTV's after a certain
number of pulls will start to sweat THEMSELVES and create
that sweaty effect your talking about... They get dry and
tough and when the heat from the resin curing creates the
moisture in the mold..

Also, theres the whole humidity issue
that can effect the resin.

The age of the resin ? Has the
pre-polymer been exposed to air for too long ?

THAT one is more of a dead give-away as the resin
get "chunky" and pretty nasty .


Sr Member
How big a pour are you doing?

If it's a big pour (1kg+) then it may be kicking as you mix and you may not be mixing it thoroughly.

If it's a small pour 50g or so then you shouldn't have a problem.

I feel embarrased asking but you are mixing 50/50 by weight? It took me 6 months before I realised 50/50 by volume was wrong.

Also as Wolvester stated if the containers have been opened for even a couple of weeks they'll have absorbed moisture and one of the parts may even be going 'crusty'.


Sr Member
I let the resin sit 30 minutes before I poured this time but I have poured immediately after shaking in the past.

I use mold release in some of the molds but not all. Some of the molds are not condusive to being sprayed because of their design.

I know some resins are to be mixed by weight and some by volume, or at least, they have different mixing directions depending on HOW you're mixing. I don't see anything on Smooth On's website regarding this.


Sr Member
I've never seen any resin that was mixed by anything but weight (once I knew what I was looking for.) But looking on smooth-on's site http://www.smooth-on.com/liqplas.htm it uses both volume & weight - that's inconvenient.

I think what's clear is that there are a lot of possibilities and advice for what works with one product may not work with yours.

It's also possible that the problem isn't your resin, but the mould - there's this piece of advice in the smooth-on FAQ:

  Common Complaint – Casting Resin Into A Newly Made “Tin” Catalyzed Silicone Mold - Newly made condensation-cure (“tin” catalyst) silicones give off alcohol and water for up to 30 days after the mold is made.  The alcohol will inhibit the cure of some resins.  Remedy:  Place the mold in an oven at 150 F / 60 C for a minimum of 4 hours or 212°F / 100°C for 4 hours to bake off residual alcohol and water.  Let mold cool to room temperature before using.


Well-Known Member
I've found that if the resin is old it sweats. I use Poly-tech easy flow 60.
The trick is to use it all right away after opening. Also dust your molds with baby powder before you pour.


Master Member
I've had pretty good luck with 'weeping' resin pieces. Normally, you just throw it away and usually not worth trying to fix it. But sometimes you don't have that option and you just have to live with what you've got. Set the oven on the lowest setting (usually "warm") and put the piece in there. Keep it in there for a while. Here's where it gets tricky. There is no perfect science as far as how long to leave it in. I just check it about every 45 minutes. When I pull it out sometimes it's tough to tell if it's still weeping. I just wipe it off and put a fresh coat of primer on. This usually forces the weeping if it's still happening. If so, throw it back in and repeat. I've found that by doing this it usually dries the piece and stops the problem.


Sr Member
Originally posted by Sidewinder@Mar 12 2006, 01:44 PM

Stir the two parts in their containers before you mix em.  Shaking doesn't always do enough.


I suspect the length of time between container shake and last pours has to do with the sweating. I'd swirl container significantly between each pour. Keeps bubbling low and ingredients from easily seperating.
I don't think it is bad resin.

May be some mold sweating as mentioned by smooth-on which could be occuring as mopold warms a bit more each time resin kicks.

Still put my money on ingredient seperation.


Sr Member
I've been gently shaking part B just before pouring. Part A is already in the cup. So far, I haven't had any more issues.



Well-Known Member
as stated already but had t oadd anyway, It could also come fro mthe mold itself since I use a 700 series from smooth-on for my molds and they tend t osweat as oppsed to silicon molds especially if they are used alot or you've just had them for a while.

either that or you just Excite them too much ;););) :lol :lol



New Member
I know what the problem is...........................I've called Smooth on about this several times and I've finally figured it out. They said it could be this or it could be that, but then my supplier told me, "ya know, we have alot of problems with 305 doing that". So, now I use 300 and have never had the problem since. My supplier always tells me that 305 is just a very unstable resin. I gotta be quick with my 300 cuz it's faster, but I never have problems now.


Sr Member
I had the same problem recently with SMOOTH ON.
I figured, it was OLD RESIN.

You can shake the crap out of it, OLD resin is OLD resin and its gonna weep.

I switched back to SILPAK SILKAST 2 and have had no problems.



Sr Member
I don't know why so many use Smooth-on, they are very expensive
and the materials are not reliable time after time.

I've used most brands out there working at different Studio shops
and each shop has their preference, the one I prefer is also a Silpak brand
called Sil-White.

It's great stuff, you can easily tint it whatever color you want, and it still
has no problems :)

Originally posted by BrundelFly@Mar 12 2006, 09:55 PM
I had the same problem recently with SMOOTH ON.
I figured, it was OLD RESIN.

You can shake the crap out of it, OLD resin is OLD resin and its gonna weep.

I switched back to SILPAK SILKAST 2 and have had no problems.

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Well-Known Member
I use Pro Cast or Poracast Mark 2 from www.monsterclub.com , Ive never had a problem with either resin . , The Procast is great for slushing and the Mark 2 for smaller pours, it has a faster demold time.