The easiest way to get into concrete is by casting into pre-made molds.
Concrete will take the shape of whatever it's poured into and can have a surprising amount of detail. A fun way to see what we're working with are with silly silicone ice molds, just make sure that you don't use them for anything edible after you've used them for concrete.
We'll use our knowledge of concrete and these fun silicone molds to make custom drawer pulls, which then you can mount to your toy chest or kitchen cabinets.
Let's get pouring!
There's loads of different types of silicone molds to choose from, and since they're inexpensive you can grab a few and have a few choices of molds.
Here are some of the ones I used in this project; there are loads of options.
Since concrete has aggregate we'll have to take that into account before starting a mix. Even pea gravel aggregate can be much too large for the small silicone ice molds, so we'll have to reduce the aggregate size to ensure we get enough concrete into the molds and aren't crowded by one large piece of aggregate.
Aggregate is used for compression strength, and since these drawer pulls aren't going to be under much load there's no need to have large aggregate in our mix.
I got an inexpensive sieve at the hardware store for $2.00, the mesh size was perfect for removing the large gravel aggregate, but left the small aggregate and sand.
After sifting a few scoops into my mixing bucket I was ready to start making my concrete.
Before pouring your concrete mix into the molds it's a good idea to use a release agent, this will make removing the concrete from the mold after it has cured very easy.
There's special concrete release agent, like Pol-Ease 230, but ordinary cooking spray works just as well.
Spray the release agent into the mold, ensuring coverage in all nooks of the mold. Careful not to spray so much that the release agent pools and causes drips.
As described in the Mixing and Pouring Lesson, mix the concrete until a good water to cement ratio is achieved, then scoop a small amount of the aggregate-free concrete mix into the molds.
Using a thin stick or skewer to poke the concrete into all areas of the mold.
Smooth and level the mold with the trowel, remove any excess concrete and clean up the edges so there's less over-pour flashing that needs to be cleaned up later when the concrete is cured.
Then, vibrate your mold to release any air bubbles and allow the mix to settle in the voids of the mold.
Using the techniques discussed earlier, vibrate the mold to release any air bubbles. Shake the mold, tap it, vibrate the table by striking a hammer around the mold, or use a power tool like a sander to cause the mold to vibrate and release any trapped bubbles.
Since these molds are silicone, you can also stretch and warp them to help get air air bubbles out in addition to the vibrating methods.
After vibrating the molds free of bubbles the mounting hardware can be added.
I used 2" fine thread machine screws with a flat hexagonal head as the mounting hardware for my drawer pulls. The hexagonal heads were gently pushed into the center of the mold.
The machine screws can stand on their own. Repeat inserting machine screws for every mold segment, ensure you don't get any concrete on the top of the machine threads.
After 24 hours the casts can be removed from the molds.
Silicone molds are great as casts can be easily removed by flexing the silicone and pushing from the underside.
Any over-pour of concrete will set around the backside of the casting, this excess pouring is called flashing and can easily be removed.
Since flashing is so thin it can be broken off with your fingers, after the edges can be smoothed over with 120 grit sandpaper.
If your drawers didn't have pulls before you'll need to drill an opening to match the diameter of the screws you used.
Since the threads go all the way into the concrete I found it nice to add a nut onto the threads first before installing into a drawer, then adding another nut after installing to hold it in place. The first nut can be adjusted to give the pull as much clearance as you need from the front face of the drawer so it can be easily grabbed.
This lesson was meant to be super simple in order to get comfortable working with concrete and understanding its properties. In our next lesson we'll look at creating voids in our concrete casts, or negative space, to make all kinds of projects.
Share a photo of your finished project with the class!
Nice work! You've completed the class project