The Ultimate Guide to DIY Molding and Resin Casting


You may find yourself in situations like wanting to replace a broken plastic part or wanting to have a spare plastic object or maybe we just feel a little artsy and feel like making some charms or maybe we are already artsy and have carved design in a foam block or something?

The answer to cater to all these needs is resin casting. Resin casting is a process in which a mold of the desired object is first made out of silicon and then pouring resin in it to make the shape.

This process is time-consuming but worth it.


In order to follow this process here is a list of items you need:

List of Items

A plastic object which is being molded ( any item that you want to make), Molding clay, Silicon rubber ( mixing ratio used 1:1 ), Casting resin (any casting resin of your choice and mixing ratio used 1:1) and Silicon mold release.

Cups for mixing all the items ( using various sizes is better ), Rolling pin, Popsicle sticks for mixing the mixture, ,Cutter, Sticky tape, Tiny paintbrush,Chipboard, A foam boards and a Ruler


The Process

Step One: Preparation of the Item Being Molded

Start with selecting the item being molded. Any item of your choice can be used, e.g. an existing plastic object or maybe an action figure to a customized foam board that was carved and shaped for any purpose of relevance.


Step Two: Preparing the Clay

Get a chunk of clay and make sure that it is a little bigger compared to the plastic object that you have selected and maintained a thickness of about 0.5 inches. Start with using more clay than needed because it is better than having less in the first place.

Next start kneading the clay and make sure it is kneaded well. kneading warms the clay up from the heat of our hands and that makes it much easier to mold.

After kneading the clay, roll the molding clay into a ball and then place it on clean and texture free surface and flatten the clay using a rolling pin. Flatten the clay little by little with care.When using a rolling pin make sure you flip the clay over and rotate it for about ¼ per turn for even distribution.

When you see that the clay is getting closer to the desired thickness, stack some pop sickle sticks and place them on either side of the clay. This will let the rolling pin give it a smooth and leveled surface.


Step Three: Making the Mold

Now take the flattened clay and place it in the center of the chipboard. Then place the piece that needs to be molded in the center of the clay. The piece may need to be deep set ( pressed completely down ) in the clay and if it is difficult to do so them remove some clay from the center.

After the plastic object is placed in the center of the clay, smoothen out the edges of clay around the object so that the silicon wont seep under the plastic object.

After the edges are smooth, take a blunt pencil, the back of a pen or a small paintbrush or any tipped item to make tiny holes close to the object and then take a tipped item with a bigger diameter to make holes around and outside the tiny holes.

These holes will help to balance both the halves so that the mixture wont slide when the curing process is on.


Step Four: Making the Box for the Mold

Take the measurement of the height and the width of our object and add about 1 inch more to it.Adding the inch gives us a border of about 0.5 inches. After this step cut a strip of the foam board and make sure that its height is an least in inch more than the object that is sticking out of the clay.

After this mark the foam strip to the appropriate measurement sand at light cuts at the marks made on the foam. This needs to be done because these light cuts will allow us to fold the board strip and make a box out of it. Once the box is made tape the edges of the four ends with masking tape.

Now place the box on the clay with the object and apply enough pressure on it that it leaves an impression on the clay. Then lift the clay and cut the clay at the impressions left on the clay.

Once the clay is cut, place the box on top of the now cut clay and if it is done well then,the clay will fit well in the box.Once it fits, seal the clay edges of the box and the chipboard.

Now add a sprue and make air holes on either side of the object. It is best decided by you on which side you want to add the sprue. Note that the sprue will leave a hole or a mark and you will have to sand it later.

To keep the sprue stable, glue it to the area when the plastic resin will be poured. Add the air holes using anything from a straw to a toothpick and glue it as well.


Step Five: Pouring the Mold

Estimate the amount needed for our first half of the pour and make sure that it is at least 0.5 inches thick than our tallest point of the object. Make sure to not cover the sprue or air holes.

Mix the proper proportion of our silicon material completely well. Pour a small amount on to the object.Just a little bit to cover it. Then take a small paintbrush and apply it evenly on the object, this way any air bubbles will be removed. Then continue pouring the rest of the mixture in the box.

Pour it from a distance to remove any air bubbles. After it is poured let it dry. The dry time is mentioned on the package of our silicon material.

Once dry, remove the clay that is securing our box to the chipboard and the clay that is at the bottom of our object . Do this step carefully and clean any residue left by the clay. Once removed add the sprue and air holes on this side if not done before.

Then use a coating of mold release onto the silicon object that is exposed. The mold release prevents the merging of the new pour and the old pour. Wipe always any mold release that gets on the object gently. Use multiple coats if needed.

If necessary, you can secure our foam box again to the chipboard with clay, but make sure that side which had the clay removed is facing upwards.

Now similar to our previous step, Estimate the amount of silicon material needed and follow the same step as before for this side. Once the mold is dry, remove the box and the clay securing it. If you used enough coats of mold release, then the mold halves should come out with ease.

Remove the object from our mold with care and keep a note of our sprue and air hole. Our mold is now ready for casting.


Step Six: Casting Our Object

Now place both the halves together and match the tiny holes/keys we made earlier. Secure them with rubber elastics. Do not over tighten them and do not damage the mold. Keep the side with the sprue and air holes facing upwards.

Now estimate the amount needed of the resin mixture and add colour if needed. Pour the mixture through the sprue. Make sure to pour it slowly. Once completed, tap the mold lightly to get rid of any air bubbles. Pour more mixture if the level of the sprue drops.

Let the resin harden and then remove the rubber band and separate the halves carefully and be mindful when removing the sprue. If the mold is not completely filled, try again but with a light rubber band hold and more tapping.


Step Seven: Cleaning of Our Final Product

The completed object may have extra material at the edges from the mold, object from the spruce and air holes. You can gently break them or cut then away with a blade, or a cutter and then smoothed it with sandpaper.

Done! There you have your final product. DIY molding and resin casting is tough but totally satisfying and worth it.

You may need to follow slightly altered steps as per as per your resin of choice but this entire process works on this method.


Written by - Lirica Machado

Edited by – Adrija Saha

Post a comment