Silicone is used for making molds for one simple reason: Nothing sticks to silicone but silicone. This is useful for making molds because the silicone mold will not stick to any walls or the item that you are making a mold off. And when you pour the mold the finished item will usually release rather easily from the silicone mold. But how do you actually make a silicone mold?
How to make a silicone mold:
- Place the item on a flat surface
- Create walls around the item with some MDF and hot glue
- Mix some two-part silicone according to the instructions
- Use an old brush to push the silicone into the details of the item
- Pour the rest of the silicone over the item until its fully covered
- Wait until the silicone has cured and then remove the walls and the item
Now you know how to make a 1-part silicone mold. Don´t worry, if you want to know exactly how to make a mold and see pictures for each step then read on!
Materials for Making Silicone Molds
First, let’s have a look at the different materials that you will need to make a silicone mold. There are quite a few but most are rather easy to get and all of them can be easily ordered online.
As a whole, the materials for making silicone molds are two-part silicone for mold making, MDF or acrylic sheets for making the walls, disposable measuring cups, some stirring sticks, an old brush, a hot glue gun, a digital scale, and some air dry clay or polymer clay.
Here is a list of all of the materials for making silicone molds:
- Liquid silicone
- MDF or Acrylic sheets
- Disposable measuring cups
- Stirring sticks
- Old brush
- Hot glue gun
- Digital scale
- Air Dry Clay or Modeling Clay
If you are not sure where you can get all of these materials and what brands are best for mold making then don´t worry. Here are my personal choices for all of the materials and tools and where you can get them.
I highly recommend using liquid silicone for most molds. You can also use silicone putty but I only recommend that for items that have very little detail.
I personally recommend the silicone mold-making kit from Let´s Resin that you can get right here on Amazon.
The silicone is easy to use, mixes in a 1 to 1 ratio and I never had any issues with bubbles when using it.
You can also get molding silicone from your local crafts store but make sure that you get silicone that is hard enough. The hardness of silicone rubber is measured in shore.
Less than 20 shore is very soft silicone that can easily tare and is not recommended for resin casting.
Between 20 and 40 shore is medium hard silicone and can be used for some resin casts.
Higher than 40 shore is hard silicone rubber and it’s usually the best fit for most resin casts.
MDF or Acrylic Sheets
You can get them in various sizes and thicknesses at your local hardware store.
I usually use 3mm thick MDF or 1mm thick acrylic sheets for most of my projects because they are easy to cut with a box cutting knife.
Hot Glue Gun
You don´t need a fancy one. I personally still use a 12$ hot glue gun that I got from my local crafts store.
Air Dry Clay or Modeling Clay
Air Dry Clay is my preferred choice for making molds but Modeling Clay or even Polymer Clay also works quite well.
You will only need clay if you are making a 2-part mold.
Polymer clay can be found in almost all craft stores nowadays. You can, however, also buy some at Amazon.
Air dry clay can also easily be found in any crafts store.
How to Make a 1-Part Mold
A 1-part mold is usually best to use for items that have one flat side with no details on it. This side will be laid flat on a surface and the silicone will be poured on top of the item.
Later the epoxy will be poured from that side and level itself through gravity creating a flat side right where it was on the original item.
For more complex molds you will need to make a 2-part mold. You can read more on that further down below.
1. Place the Item On a Flat Surface
The first step is quite important and you shouldn´t rush it even though it sounds quite simple.
Place the item, that you want to make a mold of, on a flat surface. I usually use a piece of MDF.
Make sure to place the largest side of the item down. The side you place down won´t be in contact with the silicone and thus shouldn’t have any details on it as the mold will never catch those.
You should also adhere the item to the surface with a little dot of hot glue to make sure that it won´t move while you make the silicone mold.
2. Create Walls Around the Item With Some MDF and Hot Glue
Next, you need to place some walls around the item. Make sure to leave at least 10 mm (0.5 inches) space between the item and the walls.
This padding is to ensure that the finished mold has enough strength.
I usually cut the MDF or the acrylic sheets to size with a box cutter and then glue them in place with hot glue.
Make sure to apply the hot glue all around the bottom and the edges of the walls to keep the silicone from spilling out.
3. Mix Some Two-Part Silicone According to the Instructions
Now that our item and the walls are in place we just have to pour the silicone.
So, mix the silicone in the correct ratio, as described on the packaging. It’s usually a 1-to-1 ratio.
The best way to measure the correct ratio is to use a digital scale. Place one cup on the scale and press tara to zero the scale out.
Then fill the first part (often called part A) into the cup a little less than halfway.
Remember what the scale says and press tara again. Then fill the second part of the silicone (often called part B) into the cup until it hits the same number. Now you have a perfect one-to-one ratio in the cup.
Mix the two parts thoroughly with a stirring stick or something similar.
The two parts are usually differently colored so you will be easily able to tell when they are thoroughly mixed.
4. Use an Old Brush to Push the Silicone Into the Details of the Item’s Surface
Before you pour the silicone on the item you should first make sure that the silicone catches all of the surface details of the item.
I always use an old paintbrush that I don´t need anymore to spread some of the silicone on the surface of the item. I use the brush to push the silicone in all of the little details.
5. Pour the Rest of the Silicone Over the Item Until its Fully Covered
When pouring the silicone I usually pinch the cup slightly to make the stream, in which I pour the silicone, as thin as possible.
This will eliminate a lot of potential bubbles inside the silicone.
Most good silicones for mold making will be degassing but it’s always better to be safe than sorry.
6. Wait Until the Silicone Has Cured and Then Remove the Walls and the Item
Curing times for silicone are quite different depending on the brand of the silicone.
But even the slowest curing silicones will be fully cured after 24 hours. A lot of silicones, however, will be fully cured after 3 or 4 hours.
When removing the item from the silicone mold it is often best to start tearing away the walls first. A box cutter can be helpful with this but be careful not to cut yourself or the finished mold.
After the walls are gone you can usually simply pull the silicone mold off of the item.
Don´t use too much force or you might damage the mold if the process.
And there you have it, your very first self-made mold!
I colored some resin in light red and did a test mold that turned out good. I was a little too impatient, so the resin wasn´t fully cured when I removed it from the mold resulting in some soft edges on the finished piece.
How to Make a 2-Part Mold
2-Part molds aren´t as easy to make as 1-part molds but they are sometimes needed when a simple 1-part mold isn´t possible.
If an item is round, for example, or if it has fine detail on every side then a 2-part mold is needed to catch all of the detail.
For this 2-part-mold I am using the Lion Ring from Printed Obsession. This was also printed on the Mars 2 Pro from Elegoo.
1. Embed One Half of the Model in Clay
The first thing you have to do is create the walls for the mold.
I always use MDF or Acrylic sheets to create the walls for my molds. Cut them to size with a box knife and glue them together with hot glue.
Make sure that the hot glue is all the way around the bottom of the walls and on the sides to keep any silicone from spilling out.
Then cover the bottom of the prepared mold with a layer of the clay of your choosing. I highly recommend using air dry clay
The bottom layer should be at least 5 cm (2 inches) thick.
Then press the item, that you want to make a mold of, in the bottom clay layer.
Finally fill in some more clay until the item is covered about halfway in clay. Make sure that the clay is perfectly flush with the item and with the walls.
2. Carve Some Registration Marks in the Clay
Next, you have to carve some registration marks into the clay all around the item.
These registration marks will ensure that both halves of the finished mold will fit together as accurately as possible.
I usually use the back side of a big brush to press some round dots in the clay all around the model. The more of these marks you do the easier it will be to align the two halves later on.
This is also the time to put in two round pieces that will go from the model all the way to one of the walls. These will create the sprue for casting our mold later on.
You can use a piece of small pipe or a very thick wire as a placeholder for the sprue.
Choose a place on the item that has very little detail and then press the round piece, in my case, it’s a thick wire, in the clay so that it runs from the surface of the item to the closest wall.
Then you will need another sprue where the air can escape from the mold when you pour the resin in.
So use the round piece, again I used a thick wire, and run it very close to the main sprue to the same wall. Don´t run the second sprue too close to the first one!
3. Pour the First Part of the Silicone Mold
Now it’s finally time to pour the first part of the mold.
Mix your silicone according to the instructions and use a digital scale, as described above, to accurately measure the two parts of the silicone.
Use a brush to push some of the silicone into every detail of the item and then pour the rest over the item until it’s fully covered.
4. Remove the Clay After the First Part of the Mold Has Cured
Next, remove the bottom of the mold and try to keep the walls intact.
Then remove all of the clay inside of the mold but try to keep the item and the sprue place holders in place when possible.
This step is really messy and annoying but with a little patience, you will be able to get all of the clay out.
5. Apply a Mold Release Spray to the Entire Model and Half of the Finished Mold
Then use a mold release spray to spray the whole model and the other part of the mold with it.
I used this one from Amazon, but any decent mold release spray will do. I tried a lot of them and this far all of them worked quite well.
The mold release spray will make it possible to separate the two parts of the silicone mold from each other.
6. Pour the Second Half of the Silicone Mold
Then mix the silicone again and pour the second half of the mold in the same way as you did the first part.
Once the second part of the mold has cured you can finally remove the walls of the mold and separate the two parts of the mold.
You can remove the placeholders for the sprues and the item from the mold.
Then use a small box knife to clean up parts of the mold like the beginning and the end of the sprue.
Make sure that there is no silicone rest hanging around the edges of the mold or the ends of the two sprues.
And with this, you are done. You have made your first 2-part mold!
And here is what a finished piece from the mold looks like.