Monday, February 14, 2011

How To Cast In Resin Part II

Well, we're back with another installment of "How To Cast In Resin."  Today I will be documenting the steps that I take to cast my resin pieces.  Let's get started!
     You will need everything mentioned in the previous post if you wish to follow along EXACTLY, but there are substitutions.  A few items that i may have missed in the prior post are discussed below:
     Surfactant-  This stuff is used to keep the resin from sticking to the mold and causing damage over time.  It allows your casts to slide right out of the molds.  You can use a mix of Jet Dry dishwashing detergent and water, but I prefer to use this:
       Jet Dry-  I still use the Jet Dry in a bucket of water to treat my molds prior to casting.  About a 1:10 ratio is all that is required.
Step 1:      Just soak while you are preparing the rest of the items that you will be using.  Fill up a bucket of your Jet Dry mix as a first step so you can let them sit.  When you are ready to grab your molds out, agitate them a bit with your hands as shown.  Stick your fingers down into the recesses to get out any residual powder residue.  Remember that your first cast will likely not be perfect but the subsequent casts following this will turn out nicely if all is done correctly.  You can always use the first casts for rubble.
Step 2:     Once you have your mold out of the water mix, slap it several times against a towel to remove all the water and sit it out on your work surface to air dry while you are preparing the resin.  This should do the trick if you cannot afford the mold release.  Some may prefer not to release at all, strictly preference here. 
**Note that you do not want to pour the resin into a wet mold!
 Step 3:     Measure out equal parts of A and B.  I use a scale for this.  It is not super critical, but this resin cures in under 3 minutes.  If you manage to put in more catalyst than required, it will harden even faster so please be cautious.  Also noteworthy, once this resin begins to turn white, it hardens almost immediately.  Do not take your time getting this into the mold.
Step 4:     Pour your A and B cups into a larger cup and stir together.

Step 5:     Place the mixture into a vacuum chamber and turn on the pump.  You want to get as close to 29 HG as possible, note that 30 HG is Full Vacuum.  You will notice all of the air bubbles rising to the surface, and at 29 HG, the bubbles will begin to boil up and pop.  Once this begins, you are okay to turn off the vacuum pump and SLOWLY let air back into the chamber.  If you perform this step too quickly, you will have a huge mess to clean up. 
***Remember the cure time of your resin here, taking too much time on this step will result in a block of resin in your cup.  Do not throw this out though, because i can be used as a display base if you can put it on a lathe. 
     If you do not have a vacuum chamber, there is an alternative, but this can be messy and somewhat inconsistent.  This method is known as "Bombs Away."  What you need to do is place your mold at least 2 feet below a shelf or something above your work surface.  Place the cup on this shelf and poke a very small hole in the bottom of the cup.  The resin will be allowed to escape the cup in a very thin stream where no air bubbles can collect.  Drop the resin directly in the mold and turn the mold a few times to even out the pour.  **Sorry no pics**  I think Tap Plastics does a tutorial of this method.

Step 6:     I like to place my mold in the pressure pot and pour it in there.  This keeps the mess isolated only to my pot.  Do not pour the resin into a cavity, pour it onto the top of the mold near a corner of a cavity and let the resin roll into the mold.  When you are finished pouring, put the lid on the pot and blast air into it.  Keep the pressure below 60 PSI, as you do not want to damage your pot.  Notice the closeup of my setup.  There is a ball valve located just after the input to lock the pressure in.  This is also used to let the pressure out.

     Another option would be to get a vibrating table.  Instead of pressure casting, you could set your mold on top of a vibrating table and pour it while the vibrator is on.  Not everyone has pressure pots and vacuum chambers, so I figure this is worth mentioning.  I ordered one a long time ago and it came in a discretely marked package at my doorstep.... Wonder what the neighbors thought?

Step 7:     When the resin in your cup is nice and hard, remove the mold from your pot, and de-mold your pieces.  If everything went well, you should be well on your way casting bubble free pieces.  Good luck and if there are any questions, please ask them in the comments section.


  1. How are all of these techniques working for you? I'm familiar with all of them, but never see all of them applied to resin casting.

    The water/jet dry mix is generally used with plaster casting. Resin and water normally don't mix well. I use talc (baby powder)in my molds to cut down on moisture and to help cut down on bubbles.

    Are you using a resin with a 5 minute pot life? My 3 minute resin barely gives me time to mix and pour - if I tried to vacuum the resin, I'd have a solid cup!

    I use the long drop when pouring RTV for molds, although the pressure pot you have would be much more effective.

    For an open faced mold like the Hirst molds, I find a quick scrape over the top will clear any bubbles from the surface. Deep bubbles are usually caused by air trapped in the mold itself, rather than bubbles in the resin.

  2. I use water/jet dry with no major issues. I also have some surfactant that I use from time to time when temperatures/humidity change.
    For open faced molds, I usually spray a quick shot of surfactant over the top and lay a flat piece of glass over the top of the mold. If I use this method, I will not usually pressurize.
    Also, the mold is very dependent on whether or not I pressurize the mix, because some of the quick molds I have made are not bubble free, therefore by pressurizing them, the bubbles will be severely amplified in the casts.
    I suppose that there is no SET IN STONE way to cast with resin, but I was more interested in putting up a few solid methods for people to experiment with.
    As for the gear, It is not all necessary, but comes in handy when things go wrong. I use varied pot life resins, and have had a few solid cups come out of the vacuum chamber. Gotta work quick!
    If you are interested, I'd love to compile information with you and help out our community. You do terrific work!

  3. Thanks for the tutorial. I have tried casting a few times and have had some success although I technically use plastic - oomoo smoothcast 300? I've had success with custom shoulder pads but have trouble with bigger items.

    Part of my mistake may be the vacum: I have been vacuming the plastic once in the mold to pull out the air. If I understand you correctly this would actually make bigger bubbles?