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Suggestions for 2 Part Epoxacoat Grey Mold w/o a Release Agent
I am new to this hobby/more than a hobby and am attempting to create my first full head silicone mask (referred to as a half mask). I’ve been following the videos, sculpted out the head and and neck from chavant medium, built up my clay wall, sprayed the release agent on the front side w/2 coats before beginning my mold, and finished out the front side exactly as the video instructed. When I flipped the mold over however, I got a little ahead of myself after cleaning out the last few remnants of the clay wall and immediately began with my epoxacoat grey layer on the back. I realized what I had done right away and wiped some of it away to add my pry points, but at that point it was too late to add the release agent to the back side. From there I just crossed my fingers/hoped for the best and continued on with the process until my fiberglass layers were complete. My question now is - how much trouble am I in? My front side cured about 3-4 days before I got to the back side, so will the back layer of epoxacoat grey still bond to it or will it just be more difficult (but possible) for me to pry the 2 halves apart? I guess I’ll find out tomorrow evening when I begin prying, but I’m hoping this just means cleaning out the clay will be more difficult and that I’ll have no real issue separating each half of the mold. 🤞
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Answers
What has likely happened is the two halves are permanently joined. If you try to pry them apart and find they don't budge with reasonable force (don't risk snapping anything), here's what I would do.
Use a thin-bladed hack saw to cut along the flange at the parting line, to once again create the 2 halves, but before cutting I would do a lot of prep work.
Flange prep:
Cut/grind/sand the outer flange into shape so it is nice and smooth and even all the way around. I would also make sure the outer edge of the flange is perfectly flat and as close to 90 degrees from the flange surface as possible. This will help with cutting later.
New keys:
Cut small notches all the way around the perimeter. These will be used to help visually align the mold once it's cut in two. Alternatively, you could also cut small thin slits around the edge that are the exact thickness of a known object (like a tongue depressor) so wedging those objects around the perimeter would force the mold into alignment during use. The same concept could work by drilling holes the exact diameter of some type of alignment pin. The fit would have to be snug to ensure nothing can wiggle. Just plan all your cuts so stay along the outer edge and leave plenty of room at the center for your bolt holes.
Bolt holes:
Drill bolt holes all the way around the perimeter, a couple of inches apart. These will be used to hold the mold closed like normal. I would use more bolts than a normal mold since your final seam will not be as clean due to cutting.
Marking your cut line:
Mark the parting line with a scribe or very thin pen. You'll want a clean guide as you cut to make sure you don't wander too close to a flange edge. If you feel like your flange edge would be too thin for this, you can thicken it up first.
Cut along the line:
Using the thinnest hack saw blade you can find, slowly work your way around the mold. I might even use the type of thin hack saw blade you can put into a hobby knife handle or something smaller to help prevent the cut angle from wandering. The key here is going very, very slow and focusing on accuracy. Keep the blade at a 90-degree angle to the flange surface at all times. This will take hours of patience, and you may want to take regular breaks to prevent yourself from rushing. As you work your way around, you will want to use clamps (or your bolt holes) to keep the area you've already cut together so the mold does not start to splay open as you cut, as this could add stress and damage the mold.
Once you have the mold in 2 halves you're ready to clean it up, bolt it up, and test it out. I'd first test it with water to see if/where the cut seam leaks. You may need to run hot glue around the outer edge of the flange to help seal it up before each casting. It may also help to use something like vaseline along the inner faces of the flange where you cut, to act almost like a gasket. If you find that you need to do something like this to prevent leaks, keep the applied layer super thin and towards the outside of the flange, as when the mold is bolted together it may squish out into the mold. After a water test make sure the mold is fully dry before trying to cast anything in it.
This is not something I've had to try before, just a theoretical solution.
Anyone else have any suggestions?
/Chris
After posting here and reading Chris’s suggestions, I began researching other possible solutions as well. I wanted to see if his suggestions and an additional search could generate new ideas, because one thing that kept coming to mind was the concerns about delamination, which were mentioned more than once during the instructional videos. This seemed like could offer a solution.
In my research, I found a website discussing layered epoxy coats and how the bonds between them work (chemical vs. mechanical). It described a chemical bond the strongest and requiring the layers to be adhered to one another during the first layer’s of initial setup (i.e. the point that it becomes tacky, but not enough to comes off on your gloves). A mechanical bond was described as a secondary bond, not as strong, and they recommended sanding the surface of the cured epoxy to help it stick. In my case the cured side was slick. This meant the bond created between the 2 halves was not only the weakest of the 2 bonds, but I didn’t even set up the ideal conditions (sanding) for it to stick.
When I got home the next day I began trimming down the edges with my angle grinder and was preparing myself to have to follow Chris’s suggestions. Once trimmed down, I saw my clay pry points and figured I would first give it a pry. I could definitely tell it was a solid piece at first pry, but I also noticed a hairline crack to the side of each pry point that followed the point of adhesion. Knowing it was bonded, but also knowing this bond could be a weak point to be exploited, I began alternating a flat pry bar and flathead screwdriver around the edge of the mold, chasing the line and making it continue/spread. I used a hammer at times to hammer my pry bar or screwdriver, but was careful not to try to go too deep at any given drive. After chasing the line all around the edges I went back and tried going a little deeper, a little deeper, a little wider....with each tap, breaking that mechanical bond and finally separating the 2 halves. They came out a little rough looking, definitely not as pretty as the one in the instructional video, but I think they’ll work. I’ll be finishing it out this evening and will hopefully pour my first mask later tonight. I’ll let you know how it goes and be sure to post photos if it works out.
Thank you again - crisis averted!
Sincerely,
Joshua
The Joshua Project
/Chris