This is the first time I start with the material exploration and adapt the unique material property to the furniture making. The biggest difference and challenge of this making process is that it requires a lots of tests. Everything is unsure and unpredictable. I need to explore the possibilities and causes of the problem while controlling variables.
There are five tests that I record below. You could “see” how the resin bubble was made by following me to go through all these process.
Now, let’s start the journey!
Due to the interesting material property of resin, it is soft and flexible when it is thin, it is rigid and stiff when it is thick. Since the thickness is controllable, I assume that I am able to control the softness and the hardness by changing the thickness of the resin.
TEST1: MATERIALS COMBINATION & MOLD RELEASE
Due to the time and money limit, I decide to CNC cut the foam to make two molds: inside mold and outside mold. Then I assemble the mold together and pour the resin into the mold. That’s the general idea of the making process.
I get two sheets of blue foam (polystyrene) and send them to CNC cut.
The foam will be cut in slices by CNC machine, which means I need to glue them together. So, I think I’d better do some glue test first.
Another problem is, there are so many types of resin in the market. Some of them are rigid when they are thick, but fragile when they get thin. Some of them could be soft and resistant when they are thin, but are not hard enough to support the structure.
In that case, I have to either mix different types of resin by myself or find the one that gives a perfect balance.
I select three types of resin and give a test to see if the idea of material mixture could work. All resin is ordered from Smooth-On company. The SORTA-Clear™ 18 is premium water white translucent silicone rubbers (soft); the Clear Flex™ 50 is a water white clear urethane liquid rubber compounds (medium); the EpoxAcast™ 690 is a clear casting epoxy resin (rigid).
Top-Rigid | Middle | Bottom-Soft | Mold Release |
690 | 50 | 18 | Universal Mold Release |
690 | mix | 50 | Wax |
690 | mix | 18 | Universal Mold Release |
50 | mix | 18 | Wax |
Top-Rigid | Middle | Bottom-Soft | Mold Release | Result | Reason Assumption |
690 | 50 | 18 | Universal Mold Release | Resin is rigid in the middle/ can not de-mold easily | Seems the density of 690 is larger so it tends to sink |
690 | mix | 50 | Wax | Foam melts and leaves a hole at 50 area | Temperature or chemical reaction (unsure) |
690 | mix | 18 | Universal Mold Release | Mold leaks at the bottom | Mold release might make the glue more likely to lose its stickiness |
50 | mix | 18 | Wax | Can not stick to each other | Seems that material combination is not possible |
I use resin 50 as the testing material for the mold release test. I apply two layers with both of them. The outcome seems that under the same number of layers, wax creates a better result.
Conclusion
- Material Mixture does not work – use single material by controlling the thickness
- 18 is way too soft. (mold size: 1x1x5 inch)
- Wax has a better outcome, compared to the release spray
TEST2: MATERIAL PROPERTY TEST
Top: 690 Middle: 325 Bottom: 50
(Wax as the mold release)
Material | Result | Reason |
690 | Foam is melted | The max thickness of 690 is ⅜ in, otherwise the temperature will melt the mold. |
325 | Rigid, no flexibility at all | Epoxy has less flexibility compared to rubber. |
50 | Less material -Flexible More material -Resistive | ✓ |
New problem: when the resin is curing, the heat will melt the wax. The wax will stick to the surface which makes the resin loses its transparency.
Conclusion
- Wax is not appropriate. Go back to the release spray and try to apply multiple layers on the mold.
- 50 is close to my expectation. (material determined)
TEST3: MOLD PROTECTION
I want to save some money, so I decide to use blue foam to make the mold. However, the blue foam creates tons of trouble. First, it is a porous material, which means the resin will not get a smooth surface in the mold. So, I need to paint or spray something on the foam to make the surface as smooth as I can.
Another thing is, the resin will create heat when it starts to cure. The more resin I pour into the mold, the more heat it will create during the cure time. It is important to either apply something on the mold to resist heat, or try to control and reduce heat (for example: pour the resin in a small amount by multiple times).
I apply a layer of gesso as the base to fill the porous surface, then I try three ways as the mold protection: top – shellac, middle- none, bottom-acrylic spray. Both shellac and acrylic spray could be used as sealing material.
Base | Sealing | Mold release | Result | Reason | |
Mold 1 | gesso | Shellac | Universal Mold Release | ✓ | |
Mold 2 | gesso | None | Universal Mold Release | ✓ | |
Mold 3 | gesso | Acrylic Spray | Universal Mold Release | The spray melts the foam | Chemical reactions |
CNC Cutting- outside mold and inside mold
Once the resin is cured inside the mold, I need to find a way to take the inside mold out. That is why I slice the inside mold into small sections. Also, to make sure I am able to pull the section out, I insert wood dowels into the foam mold and use glue gun to secure them.
For the outside mode, I add some wood blocks along the edge. Because the outside mold is divided into two parts so the cured resin could come out from the mold, there is a gap between two parts. The function of the wood block is to provide a surface for clamps to tighten the mold so the liquid resin will not leak through the gap.
Conclusion
- Gesso could cover the porous foam and offer a better and smoother surface
- With or without shellac does not affect the outcome. However, the clear flex 50 will create heat that could up to 180 degrees F. The more material I pour, the higher the temperature will be. Shellac starts to soften at about 150 degrees F.
- So, Gesso plus Mold release will work
TEST4: GAP FILLER TEST
Filler | Result | Reason | |
Wax | Gesso | Gesso cannot work with wax. Cracks on the surface | Gesso is water soluble, while wax is waterproof. |
Hot glue | Gesso | ✓ |
Seven layers of gesso on the mold.
Gesso could be sanded between layers to get a finer surface.
Gesso takes 30 minutes to dry and be ready to sand. However, It need to be settled for 24 hours before applying anything contains oil
Conclusion
Section: | Application: | Status: |
Casting material | Clear Flex 50 | Confirmed |
Mold -inside and outside | Blue foam | Confirmed |
Mold protection | Gesso + Mold release | Confirmed |
Gap filler | Hot glue | Confirmed |
TEST5: RESIN LAMINATION TEST
To control the heat, I plan to reduce the amount of resin for pouring each time. However, there is a line between each layer and it is quite visible.
The pot life of resin 50 is about 25 min, and the cure time is 16 hours. However, it takes 2-3 days to completely settled and is not tacky on the surface (see the fingerprints on the surface). According to the suggestion from Smooth-On technician, I give 4 hours between two layers for testing.
Through the photo I upload above, you could see that the line is not visible from certain angles.
The reason of the appearance of the line: the resin will shrink during the curing process, the longer time I wait between layers, the more visible the line will be.
The vacuum chamber is a perfect method to remove bubbles from the liquid resin. But a vacuum chamber is expensive and I am broke. So, I try the hot water and it works fine.
Conclusion
- Hot water(50 degrees C/ 12 min) works well
- Pour the resin between 1 to 4 hours between each layer. (The more resin I pour in one time, the more heat the resin will create, and the faster the resin will cure)
Final Project Starts!
Accident 1: Same process but different result- resin cures faster than expected. I assume that is because there is more resin in the bucket compared to my test. So, more heat is created in a short time, which cause a mixture of liquid resin and half-cured resin in the bucket.
Accident 2: the resin leaks from a crack on the foam mold. To ensure the two parts of the outside mold could combine to each other tightly, I use maybe too much strength on the clamp, which cause the crack. To fix the problem, I use the hot glue to cover the crack and stop the resin from leaking.
Accident 3: The amount of resin I poured is less than the amount I calculated on computer. It might because of the change of the thickness since I applied multiple layers of gesso on both inside and outside mold, or it might because of the jelly stuff I poured in the first time blocked in some place in the mold and created a cavity.
Accident 4: The good thing is, the resin cures successfully. The bad thing is, the mold cannot be pulled from the inside separately. The multiple-layered gesso, the hot glue filler, the pressure from the cured resin…all these elements could lead to this situation. I have to destroy the inside mold to take the foam out.
Because of the flexibility of the material, I decide to take the outside mold out first
Accident 5: Separation between layers. I assume that is because each time I pour the liquid resin into the mold, the resin will take away part of the mold release from the surface, which created a disconnection between layers.
So, I use the clear silicone in the photo I showed above as a glue and also the gap filler to fix the problem. Fortunately, it works well.
I hope I made the process clear and understandable to you. And I hope you enjoyed the reading. Now you know how to create a resin bubble from scratch.
A friendly suggestion from Yuya: a silicone mold could be expensive for a large scale object, but definitely create less trouble during the process. If you have money but do not have time, do silicone; if you have time but do not have money, try foam mold; if you have both time and money, wow, then you are a life winner and please do leave your name below so I could know you lol.
Information Resource/ Credit to:
- Smooth-on Technical support
- Bank Building technician-Warren Joe
- RISD 3d store faculties
- Google and youtube
- Help and advices from Anna and other classmates
