Creating Silicone Molds

The next part of my frag plug DIY project involves making silicone molds. I was not happy with how inconsistent the sand molds were producing so I wanted to create something more precise. After several attempts I am ready to share some results and learning experiences!

What I used

I am using GE Silicone 1 as it’s 100% silicone and even listed as safe for incidental food contact. Typically in the reef community we like to use things that are rated as food safe because it means there aren’t likely to be any dangerous chemicals leaking out of it. I am also using a caulk gun to dispense the silicone, a bucket to hold water and/or frag plugs, and later I used soap. I used my regular kitchen soap I use to wash dishes with.

GE silicone 1 is 100% silicone

First attempt

My first attempt was a big learning experience. I am sharing it so that you don’t make the same mistakes I did!

I started by getting a small plastic container deeper then my frag plugs. I arranged the frag plugs with the top (the part the corals get attached to) facing down. I opened up a silicone mold, punctured the seal, put in my gun and started pouring over the top of the plugs. My thinking was that the silicone would settle and fill all the crevices. It did not. At all. It left a bunch of air pockets at the bottom of the mold that I could see.

I let it sit overnight and checked it out. The top was dry but the bottom was not. I let it sit now for several days before I tried to remove the mold from the plastic container. Much to my surprise, the silicone in the middle was still as wet as ever! I let it sit a few more days before I eventually got tired of waiting and just pulled it out. Almost a week and the silicone inside was still leaking all over the place. I decided this was not good and researched some more about making molds.

Second attempt

After researching some methods to making silicone molds I tried a method using soap, water, and silicone. First I filled a tub with room temp water and added soap. I didn’t use a lot of soap just a little. Mixed it in slightly and poured the silicone left from my first attempt into the water.

I mixed it up with my hands under the water for a few minutes, hoping to make it not sticky. After a few minutes I got impatient and called it good. I made a lump and pushed two little frag plugs into the mold and let it sit for a couple of hours.

When I came back it had all set! I was surprised and it took some elbow grease but I pulled the plugs back out of the silicone. The problem with this mold was that I didn’t take the time to level the top of the mold. When I put clay into the mold to try it out, the resulting plugs were uneven at the surface. It was far better than my first attempt but it still needed to be refined.

Third attempt

Here is where my products began to really shine. Following the same process above, I mixed water and soap. Only this time I used quite a bit more soap. I actually grabbed my large container of soap and just dumped a bunch in, compared with the first time when I used a couple pumps from the kitchen sink.

This time I also did not use food prep gloves and chose to use my bare hands instead. I covered them with a layer of soap before I grabbed the silicone in the water and began working it. It did only take a minute before it stopped sticking to my hands and I could knead it above the water. I would pull it apart, dunk in the soap water, knead it back together over and over. After about 5 minutes of doing this I rolled it into a ball with my hands then slightly squished it to make a thick disk. I pressed 4 plugs into this mold and made sure to press on the surface of the whole thing lightly to make it level.

After waiting about 10 minutes I tried to pull the plugs out. They came out with almost no effort at all and the mold itself was almost completely set. It was set enough at least that it retained the shapes of the plugs with no issues. I let it dry a couple hours before putting clay into it. I decided to stick this in the freezer to see what my plugs looked like faster. It took about an hour for the wet clay to freeze enough that I could pull them out but the products now looked far superior.

I had good enough luck with this mold I actually made a second mold using the same process. It once again produced an exact replica of my other mold and I set it up using pure portland cement to see how the cement would work in it. The next morning, roughly 15 hours of set time, the cement popped right out making perfect little plugs.

My next goal is to create a silicone mold that I can pour out over frag plugs but for the time being I have been able to create molds to make a dozen frag plugs at a time. I hope this helps you create your own silicone molds and if you make any comment below with pictures!

Step by step instructions

Step 1 – get your materials together in one place. I used an old dog water bowl I had laying around, my regular kitchen soap, tap water and GE silicone 1.

Step 2 – cut the tip off the silicone bottle. I used to cut the tip right at the top but realized that I can actually cut down towards the bottom to make puncturing the bottle easier. Either way doesn’t really matter for our molds it’s just preference here where you cut.

Step 3 – fill your bowl with water and soap. Mix the soap gently until it is totally mixed and you don’t see soap spots or streaks in the water.

Step 4 – load the caulk gun (if needed) and puncture the foil.

Step 5 – pour the silicone into the bowl of soap water. Depending how big your mold is will depend on how much you need. For 4 small frag plugs, about a third of the bottle. For my 4 large frag plug mold I used around half the bottle. It may take a little trial and error here to get the amount correct but it’s OK if your mold is bigger than needed.

Step 6 – this is a really important step. BEFORE you start to work the silicone you must COAT your hands with your soap. I mean coat them well, don’t skimp or that silicone will attach to your hand really well. It’s like the movie Alien where those creepy hatch-lings grab onto people and never let go. Yeah, that’s silicone for you too.

Step 7 – grab the silicone with your bare hands. I do not recommend food gloves here as no matter what the silicone grabs onto it really bad. You can use gloves but be aware it actually makes a big mess. Start to work the silicone under the soap water just mixing it and pulling it apart, mixing it again to create a big blob you can knead.

Step 8 – now you can start to knead the silicone above the water, it should be starting to turn a white color if you used clear silicone like I did. This is good, it means it is starting to set.

Step 9 – once it has turned a nice white color all over and doesn’t stick really bad, place it on a table surface and form it into a thick disk. I make the disk by rolling the silicone in my hands to make a ball then press gently with my palms to create a disk before putting on my table.

Step 10 – place your items into the mold slowly and carefully. Be aware of where you place things if you want to fit more than 1 items in the mold.

Step 11 – let the silicone sit and set up for 10-15 minutes. Then just pull your items out of the mold. They should come out really easily here. If you leave the silicone to set up too long, like an hour, I found the items a bit harder to remove. If the mold squishes and changes shape at all when you pick it up, put it back down and wait another 5 minutes or so.

That’s it! You just created a silicone mold for yourself. I like to allow the mold to set up for another 30 minutes or so before I start to add clay. I’ll make another post about making the frag plugs using these silicone molds. It’s really quite simple. If you make your own molds for anything be sure to comment below with pictures!


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