[Archive] Need help with Resin


I need help with casting resin. I need to know how to cast in resin and not get air bubbles in the center of the cast. I do not get air bubbles on the outside, but the inside is air bubbly. Would better resin help? When I first got the resin it did not do this, but now it does. Does resin get old?


Resin does suffer from age if stored for long periods in less than optimal conditions. More likely though something else is happening. Soon after i began fiddling with casting i woulld place my moulds on my clothes washer/dryer as i was doing a load of laundry. The vibratory effect does help the trapped air to vent.

Later i picked up some vibrating motors used for massage chairs such, attaching them too a table and turning them on during the casting process. Which seemed to help greatly. By this time i was also using a higher quality resin than i started with.

When you started with this resin, you mention it didnt give you the air pocket fill centers, if its doing it now it may be time for new resin. However now that i think about it… the first casting resin/plastic i used was a 2 part where you poured the amount of resin you thought you needed into a mixing cup… then added catalyst drops based on the overall thickness of resin to be cast. This did create some very interesting effects including excessive bubbling as the chemical reactions took place. Some peices came out virtually useless with the excessive amounts of bubbles and cracking.

Now i use a virtually self venting casting medium and do not have as much trouble with said bubbles. But it is a very viscous medium so i do end up with some surface bubbling. For casts that require a greater degree of quality i use a less viscous medium and a vibrating motor attached to the casting table.

What can be done depending on the type of mould as this works best with 1 peice mould - is the slam method. Fill you mould with resin… pick up your mould a few inches and drop/slam it flat onto the table a few times to help release and bring the trapped air to the surface and break the bubbles. A very sturdy mould is best for this.

There are some other things that could done depending on the materials your using.


It seems a vacuum chamber gets rid of unwanted bubbles.

Depending on your tech-level there are several alternatives I’ve come to understand.


I live in the US does anyone know of good resin located here, or that I can order in?


there are many good resourses stateside, MicroMark makes some nice low viscosity resins, Alumilite corporation has some nice products that work very well with each other as well as a tutorial section, smooth-on corporation has large selection of resins and rubber for a variety of casting needs as well as instructional tutorials/galleries.

Alumilite and MicroMark CR may be available at some local hobby/model stores in addition to online orderings.

As with most things there are pro’s and con’s to just about all of them. Alimilite can set up in 3-7 min per cast, Micro Mark has a 30min and 60min demould vairients. Both have silicone rubber that sets up in about 4 hours.

there are more, just have to poke around and eventually take the plunge to see what works for you. To capture really fine detials i would recommend the micromark cr600 over the alumilite products. Setting time is longer but you can dust the mould with casting grade talcum powder which will absorb into the resin and pull it into details. Really all depends on what your trying to accomplish and what level you want to do it at.

have funs.


Check also for Smooth-On Ultra-low viscosity resins. They are so thin that air bubbles will rise to the top. Comes in a variety of bloom/cure times as well. Generally, if you’re worried about air bubbles, get a long bloom/cure time. I think the part #s are SC-300, SC-305 or SC-310s.