How to build an epoxy mold form
So, you have your new slab picked out and in the shop. But now you need to build a form so you can pour the epoxy. Let’s go over some tips and tricks on how to make your first time successful. We will go over a three-pronged approach to sealing the form to prevent any leaks! The links are affiliate links so I do receive compensation if you purchase from that link. Any amount of help helps a small business like mine!
I used melamine for the form since it is so smooth. There needs to be enough melamine to have your bottom and walls taller than your slab. After I trimmed the length of the slab to slightly oversized, I determined I would need two sheets of ¾” melamine to ensure I had enough.
Trim Form to Size
Cut your bottom piece of melamine to the length of your trimmed slab, plus 1 ¾” extra. This allows room for the side walls to be attached. The width can be about ¼” oversized. The walls on each end will be in between your side walls. You only need to add enough extra width here to cut your final table to square. Any extra width will just be waste, as you will have to pour more epoxy, and your wood will get smaller.
Rip your side walls to an inch taller than your slab. My slab was 3 inches thick, so I ripped mine to 4 inches. Your side walls are the same length as your bottom piece of melamine. Next, the end walls need to fit within your side walls. After ripping them to width, cut them to length. The length is the width of your bottom melamine, minus the thickness of your side walls, about 1 ½” inches.
Tyvek Tape
Tyvek tape is not required, but epoxy is very expensive therefore I want to take every precaution possible. While Tyvek tape isn’t cheap, I would gladly pay the $20-$40 in tape to keep $1,5000 worth of epoxy off my shop floor. I recommend using Tyvek tape on all the faces of the melamine that is facing the work piece.
Assemble and Caulk Form
I researched many different methods of assembling the form and how to caulk it. Many of the videos I watched were of catastrophic failures and massive leaks and how they changed their process. I adopted Cam’s method from Blacktail Studio since it is as bulletproof as you can get.
The type of caulk is somewhat important. Silicone tends to work too well making it very challenging to get your form apart. Silicone also tends to bond with epoxy causing more work in the long run. This is one of the times the cheap option is actually the best option. I use the Alex Fast caulk, specifically the waterproof version.
This caulking method consists of three parts. Each creates one more barrier in case the one prior fails. First, caulk the bottom edge of your walls. This helps create a seal underneath the walls. Your walls need to be placed on top of your main piece of melamine. The reason being, if your seam is on the bottom of the table, it’s hard to determine where the leak is coming from since you can’t see the whole bottom.
I deviate slightly from Blacktail Studio’s method by using screws instead of nails like he does. I just find it easier and more secure for me. Make sure to predrill, countersink, and screw in from the bottom.
Once all your walls are installed, we need to caulk the inside seam. Run a bead of caulk down the interior seam of the form, including the vertical seams. You can use a tool, or just your finger, but clean up the excess and ensure it is properly filling the seam. This is going to leave excess on your tool or finger. Instead of throwing it away, wipe it on the outside seam of the form. This is our third line of defense. Do this as much as you can and fill any spots you didn’t have enough with more caulk from the tube.
Perfect! Your form is almost ready! Don’t rush it and try to immediately pour epoxy. Even though the caulk says it is “dry” or “paintable” within 30 minutes to an hour, it truly needs time to dry properly and cure. I suggest leaving it overnight to make sure it’s done properly. In the next article, we will complete the final step for the mold and pour epoxy!
