Lasers, silicone, and concrete oh my!! We love making things that serve multiple purposes and had this idea to make a candle holder that works for tapered candles and tealights. In this tutorial, we'll go over how we 3D printed a mold master, made a silicone mold from it, and cast concrete using that mold.

Things we used (affiliate)

Quikrete non-shrink precision grout https://goo.gl/uB6pGS
Similar Quikrete grout (available online) https://amzn.to/2Lj6rdp
Silicone https://amzn.to/2stJNYZ
Clear acrylic spray paint (to seal) https://amzn.to/2JoXGRN
Release spray https://amzn.to/2HeJjuq
Peopoly Moai https://goo.gl/kKuTqz
Resin https://goo.gl/79jieT

Step 1: 3D Print Master Model

There are lots of ways to use 3D prints to make silicone molds, but we'll briefly touch on two methods we've tried.

For this project, we used a stereolithography (SLA) 3D printer (the Peopoly Moai) to print the model at 0.1 mm. We've shared the 3D file via Thingiverse here.

We cover the printer and printing process more in our video here, but in a nutshell it's a resin print and it comes out of the printer covered in liquid resin goo. You clean it off by shaking it in alcohol for 30 seconds, water for 30 seconds, then alcohol for another 30, and water for another 30. We've used mason jars for this with success, but had to use plastic bags for this particular print because it was so large. The bags are alright but watch out for leaks!

After cleaning the print, you cure it in UV light either in a UV box or in the sun. For the box, we lined the inside of a cardboard box with foil (attached with spray adhesive), cut a hole in the top for a UV light, and placed a small solar powered turntable on the inside for the print to sit on. We go over it in more details in the video we mentioned above.

If you don't have access to an SLA printer, we've used fused filament fabrication (FFF/FDM) 3D printers before and they can totally work too, but they require more hands-on finishing. (see the last photo in this step to see an example). We use a combination of automotive primer and sanding, repeating coats and sanding in between each until it's smooth. You can see the process here where we concrete cast a self watering planter.

Step 2: Prep Master Mold (seal and Release)

Once your print is cured (if you used SLA) or primed/sanded (if you used FFF), you're ready to prep it for the silicone! To play it safe, we sprayed on a couple coats of clear acrylic to seal it off, then we applied one coat of mold release so that the silicone wouldn't stick.

Step 3: Prep & Pour Silicone

So we actually attempted the silicone step of this project twice. The first time, we used platinum cure silicone and it did not cure at all, then when we tried to remove it the 3D print broke. Sad day. So the second time, we tried tin cure silicone and it worked like a charm!!!

It's a 2-part silicone, and you stir up each part to make sure nothing is settled at the bottom. You then pour equal amounts into separate containers, then add the blue to the pink and mix mix mix til it's all uniform.

The main challenge is avoiding bubbles, and here are 2 tips we use that help to get rid of them. Tip one is using a sander (without the sandpaper) to vibrate the container. The vibrations raise the bubbles to the top and they pop. The second method is pour a really skinny stream of silicone into your mold. It's harder for bubbles to form during the pour that way. You can also vibrate or tap the mold once the silicone is in it. Let it cure according to the directions on the package.

Step 4: Demold Silicone

There's no single method to demolding silicone, but we've torn molds in the past so you have to have a little patience. For this mold, we used wooden sticks to break the suction and give us something to grab the silicone with without having to get our fingers in there. We grabbed the group of sticks and wiggled them while also pulling out til it came loose and popped out.

Step 5: Cast Concrete

We used Quikrete Precision Grout for this project because it can get into detailed molds and is nice and strong. Full disclosure, they did sponsor the video we made, but we've been using Quikrete for a long time.

Follow the directions on the bag to get the right liquid ratio. We always start by adding the concrete mix to our bucket first, then adding the water a little bit at a time. For this particular concrete, you know you have the right consistency when it looks like the 4th picture here and does not pour out of the bucket when you tilt it.

We spooned about half of it in and then tapped the mold rapidly to bring any concrete bubbles to the surface. Then we spooned in the rest and tapped it again. We had overfilled it a little bit, so we scraped off the excess and gave it one last tapping. Then we let it cure!

Step 6: Removing Concrete Casting

Again, being careful is key here. First we gently break off any of the thin concrete overhang at the top (it's easy if you pull the mold back a little with your fingers and brush them down the little overhanging bits, they should crack right off).

For this shape, the candle holder is bigger at the base than at the top, so it was a little tricky to pull out. The best way was by first pushing from the base top pop the top out just enough to get a good grip on it. Then we could pull and wiggle til it popped out.

It turned out really good! Our lines, corners, and points all stayed sharp!

Step 7: Enjoy!

We love how these turned out! Both tea lights and taper candles work really well in them. In the end, we made 3 of them but we are excited that we have a mold we can make more from if we want!

If you wanna see more projects we've made, you can check out our YouTube channel here or find us on Instagram at @evanandkatelyn. This post contains affiliate links - thanks for the support!