Building an epoxy casting mold is a key step when creating a river table or any large casting project. This guide will take you step-by-step through the process of building your own mold.
Prepare Your Workspace
Set up a worktable where you can build and use your mold. You should be able to reach all parts of the inner mold cavity easily. A sheet of polyethylene (vapor barrier will suffice) can be placed over the worktable to ensure that clean-up is quick and easy. We recommend taping the edges of the polyethylene sheet securely to the table.
Choose Your Materials
We recommend using melamine, medium density fibreboard (MDF), or smooth plywood for the base and walls. If you are wondering about other materials for your mold surface, see below for a list of materials that epoxy will and will not stick to.
Epoxy will stick to:
Epoxy will not stick to:
· Sheathing tape/Tuck tape
· High Density Polyethylene (HDPE)
Design Your Mold
Below is a sketch showing the basic design of a mold. When planning your mold, make sure to account for wall thickness when cutting pieces to size. Make sure the walls are taller than the wood slab or embedded item. We recommend a ½” above the top of the pour.
Extending the surface of the base as shown above will allow you to see your seams in case you have a leak to patch during your pour. This will also provide leverage when you need to disassemble the mold at the end once your piece has cured.
*Note, the images used in this tutorial do not include the ½” extended mold base. However, the use of the extended base is still recommended.
Prevent Adhesion To Your Mold
Cover all of your mold cavity surfaces with sheathing tape such as Tuck tape or Tyvek tape. This will help prevent the epoxy from sticking to the mold and allows for easy removal of your casted item once the resin has cured. Ensure the tape is completely flat and sealed to the mold surface.
Assemble Your Mold
Once every surface of the mold cavity is covered in sheathing tape, drill pilot holes to assist with assembling the walls and base. Apply a bead of silicone to the bottom of the walls to create a butt joint where the walls meet the base of the mold. Assemble the walls and base using screws and the pilot holes. We recommend using screws for assembly to make it easier to disassemble the mold once your project is complete, and to increase the chance that your mold can be re-used for a future project.
Seal Your Mold
Ensure the mold cavity is clean of dust and contaminants before you seal the edges. Use a lint free cloth with denatured alcohol to remove any dust or debris from the mold cavity. Along all the inner joints, apply a fillet of silicone to ensure the epoxy will not be able to leak out of the mold. Creating this fillet is similar to caulking a bathtub.
Make sure the silicone is spread properly to fill all of the seams. Allow the silicone to set before pouring epoxy into the mold. Please refer to silicone manufacturer instructions for set time. Once the silicone is set, clean your mold cavity another time with a lint free cloth and denatured alcohol.
Tip: If this is your first project, consider adding a fillet of silicone to the outer edges of the walls and base to guard against leaks.
Get Your Project Ready To Pour
Level the mold on the worktable. If required, place the mold on wooden blocks (or similar) to allow access to the bottom of the mold for clamping wood slabs or other embedded objects. Adjust level as necessary with wood shims, washers, or other items available in your shop space.
Next, you can add your wood slab or embedded item to the mold cavity. Be sure to clamp down the object to avoid having it float during the casting process. Use a block of wood covered in sheathing tape between the wood and the clamp, to ensure the clamp does not bond to your project.
Warning: If your wood slab is warped, excessive clamping force can cause the mold to warp as well. Adding a stiffener, like a second thickness of mdf, to the base will help prevent the mold from twisting.
Mix and Pour Your Epoxy
Your preparation is complete and you’re ready to pour. Please refer to the FlowCast® Application Info Sheet for casting information and directions regarding mix ratio, pour depth, multi-layer pours, and cure time.
Demolding Your Project
Once your project is fully cured, you can remove the walls of the mold and use a putty knife or crowbar to gently remove the casting from the mold. The added base material will provide leverage points for demolding.