Resin Addict Forum

Well after noticing the beginning of some deterioration on one of my SAW kit moulds, I'm now using release spray after every cast. So I wanted to instigate a bit of a discussion about release agents.

The primary purpose of the release agent is to prevent the resin from sticking to the silicone mould. At first this may seem silly, as the only thing that seems to bond to silicone is more silicone! But just because the silicone and resin don't bond, they still do stick together slightly and in the process of demoulding a bit of extra stress is placed on the mould. By giving the mould a release coating, the resin sticks to the silicone much less readily and the difference is very noticeable when removing the part from the mould.

The secondary purpose of the release agent is to help prevent bubbles (the ones that aren't going to be compressed small enough from the pressure) from sticking to the silicone and thus rise up and out the vent(s).

On an uneducated whim a while ago I bought some Mann Ease Release 200 spray. I don't use anywhere near as much as the instructions on the can specify. I just give the mould a light misting now each time after I demould. I'm not sure now well it works for preventing bubbles sticking, but for that I use a second agent in conjunction with the Ease Release 200: talcum powder.

I picked up a big bottle of baby powder for only a couple of bucks. It smells nice
When preparing a mould for a cast, I pour it into the mould and then use a big soft brush to dust it all around. Then I hold the mould upside down over a bin and tap the excess (most of the talc) out.

So has anybody else had any experience with other release agents?
How much do you use?
Is there much difference between the different brands?
Do you use the same release for both resin to silicone and silicone to silicone?
Do you notice a significant improvement in mould longevity when using the release?

On a related note, the release agent I use for silicone to silicone (in two part moulds, etc.) is good old Vaseline. It's cheap, easy to get a hold of and works fantastically. I bought it in this little metal tin (it's an aloe vera one that's intended for dry lips) and to use, I simply spatula a bit into the lid and use a lighter under the lid to melt it down nice and runny. Then I just brush it on. Easy!

I use a spray on release agent for the silicon-resin step which definately helps and I also have started using a very light dusting to baby powder to help reduce bubbles which seems to work fairly well. I definately notice a lot less pull when trying to remove the cast piece so I know the release agent is working.

The rubber to rubber stuff I use is brush on by micromark and seems to work fine on any type of silicon. I don't use it on the resin though because it causes some sort of reaction that makes it sticky and doesn't wash away. As a result my first inital cast on any new mold set is usually a throw away as it's almost always sticky. But once that inital cast is done it doesn't seem to have any negative effect on later casts.

Micromark sells a silicon extended which is supposed to help double the life of mold, and can be used to help keep it from degrading while being stored for long periods. Basically it replaces many of the oils that the resin casting process leeches out over time which causes it to dry out and split.

Micro-mark also has some info on their site about "mold baking" which is reheating the mold up to about 200 degrees. This allows the silicon to reabsorb some of the oils that are leeching outwards but it's not quite hot enough for the mold to melt or burn. They recommend reguarly rebaking the mold and adding extender to get maximum life out of the silicon. If their information is correct you can take a mold that normally may see around 50 copies and get upwards to 200 out of it.

I haven't tried it first hand yet, but it may be worth checking out.

Thanks Jon. I've heard the concept of baking the moulds before, but not been inspired to try it. I do notice that some of my older original moulds have discoloured in the spots that have some into contact with the resin, so perhaps I can do a test bake with one of them...

I use the Stoner Rocket Release

A quick spray after every second casting and the moulds do last a lot longer. I use talc on the more fiddly moulds.

I use Stoner Rapid Release to prevent bonding between two part mould halves, though Rocket Release will also do the job. Rapid Release really stinks.

http://www.moldmoreparts.com/E302txt.htm

How does the talcum powder thing work??
And when is it applied??

A light dusting of talcum powder aka baby powder helps give the surface have a tiny amount of grit to it which helps break up bubbles in trouble spots. Air clings to smooth surfaces when it's suspended in a liquid, simular to how bubbles stick to the inside of a glass of water. Most the time you can knock those bubbles loose by taping the molds but sometimes you will get bubbles trapped in the undercut areas that no amount of banging the mold will dislodge.

The baby powder helps break the bubbles ability to bond with a flat/smooth surface and causes it to float up and out as the resin fills the mold cavity.

It works well with a spray on release agent, get a nice smooth layer of spray release and let it dry for 5-10 minutes. Once the release is completely dry give the mold halves a dusting with baby powder using a small brush. Put a good amount on that way it gets in all the recesses. Then turn the mold over and gives it a couple light taps against the table, or tray. You should be left with a very light dusting of the powder, you shouldn't see any large white spots, just a nice smooth dusting.

If you are getting caking and the baby powder is clinging to the mold in clumps it probably means your mold release wasn't dry. It may not work well if you are using oil based releases, vaseline etc as they will remain wet or sticky which will cause the powder to clump.

You may even be able to skip the mold release entirely and use the pwder as a release agent, but personally I prefer to use the release just to be safe. You may have to give the molds a rinse in water every now and then t help get rid of left over powder that'll build up in the areas surround the mold detail. Just make sure the mold is completely dry after cleaning it out as any left over water will cause the resin to boil and the first casting after cleaning will be bad if there's any moisture in the molds.

If you want to get more than a few casts out of your molds you have to use mold release each time you cast. If you skip on the release you'll be lucky to get 5-10 copies out of the mold. Those same molds using release can last you hundreds of copies. The silicon I use they generallys ay will get about 50 copies before it wears out, I've pulled upwards to 250 copies out of the same mold when I make sure to use release every time. It really increases the life of the molds dramatically.


If you are going to be doing regular amounts of casting make sure to ventilate the room well and pick up a breather mask, get the gas mask style ones and not just the thin paper ones. There's a lot of chemical vapors coming off the resin and the release agents, and while it may not be deadly you don't want to be breathing it in. A good grade mask will run about $25 at home depot make sure it's one rated for paint & pesticides as they sell two version, one for chemicals and one rated only for dust.

With the huge volume of stuff I've been casting lately I was starting to get lots of headaches and dizzy spells, and I even started getting a slight cough. As soon as I picked up the breather all of that went away and it works great, also has a nice benefit of completely eliminating the funky resin smell.

Well Jon has really covered all bases there so not much left for me to add! If trying to do things on the cheap and you only need a few copies then you can get away with just the talc powder, but if the parts have a bit of complexity you're still going to need pressure and possibly vacuum to get perfect casts.