Are you feeling inspired to try something new with concrete? Follow the steps below to create your own concrete iPad stand or have some fun and create something of your own by adapting this great step-by-step tutorial.
You will need:
- An empty plastic-lined carton, the size of a large popcorn box (the kind you get at the movies)
- Styrofoam (small scrap pieces)
- Wood, about 12cm thick
- 2-part epoxy
- Permanent marker
- Clear packaging tape
- Hand saw (fine/medium teeth)
- Razor blade/utility knife
- Sandpaper/handheld diamond polishing pad
- Slotted screw driver
- 1/16" drill bit
- Silicone (100% silicone, window and door sealant)
- Rubber gloves
- Safety glasses
- Buckets for mixing
- Plastic scraper
Step 1: Measure, mark and cut the carton
1. Mark two adjacent corners at around 17cm and the other two at around 15cm. Draw four lines connecting the dots with the permanent marker. This is the cut line.
2. To help support the plastic container while cutting, cut a Styrofoam block, about 7cm X 7cm, and push it in the opening of the form.
3. Starting from one corner gently saw back and forth to start a straight cut. Go slowly at first, alternating back and forth between corners until you can connect the slices and cut through. Repeat on the remaining sides until the cut is complete.
4. Clean up the edges of the plastic with some rough sand paper (80-100 grit) and be careful not to scratch the inside of the form (any scratches WILL be transferred to the concrete).
Step 2: Make, tape, silicone and install the knockout
A knockout is a piece of foam, rubber, plastic, felt etc. that is secured inside the form in order to create a void, recess, or opening in the concrete. For this piece we'll use a small knockout to create a recess for the "shelf" to slide into. This recess only needs to be about a half a centimetre thick if you're going to glue the shelf in place. We can make a knockout from scrap Styrofoam, or we can use thick felt with an adhesive backing (for furniture to keep it from scratching the floor).
To make the Styrofoam knockout:
1. Rough cut a small piece of Styrofoam with a saw or utility knife into a rectangle and sand down to 4cm wide X 1cm tall X 0.5cm deep.
2. Wrap the Styrofoam neatly with clear packing tape. This will keep it from bonding to the concrete and will give us a smooth surface.
3. It might be helpful to make a small cardboard template to use as a guide to centre the knockout in the form. Apply a thin coat of silicone to one of the 4cm faces and press it down into the form. Wipe away any excess silicone that squeezes out and wait a few hours for it to cure.
4. Drill or cut a small hole about 1/8 cm in size behind the knockout and install a short 2.5cm screw so the knockout doesn't float away during the pour. (The silicone is going to keep concrete from seeping between the knockout and the form wall. If that happens, the knockout will move around and could be lost completely. The silicone is also keeping the foam from floating to the surface — foam floats in water and concrete contains water — the screw will hold the foam just in case the silicone does not).
5. After the silicone has completely cured (at least 3-6 hours and up to 24), remove the excess with denatured alcohol and blow any debris out of the form.
How to make the adhesive backed felt knockout:
1. Find some heavy duty felt with an adhesive back, cut down to the size of the knockout, stack two or three pieces together.
2. Wrap the stack of felt pieces in clear tape, peel off adhesive backing and fix to the inside of the form. The advantage of this method is that you don't have to wait for the silicone to dry. The disadvantage is finding and paying for the felt!
Step 3: Mix, Pour, Vibrate, Cover + Cure the Concrete
Weighing out dry materials should be done somewhere with proper ventilation and it's a good idea to wear a particle mask if you're doing it often. Small projects like this can be mixed by hand. It's best to wear rubber gloves and work in a space that is easy to clean up. It's also a good habit to start with clean tools, buckets, and especially a clean workspace so we don't accidentally get pieces of dirt or Styrofoam in our batch of freshly mixed concrete.
Normal sacked concrete will be cured enough to de-mould in about 5 days. Smaller projects like this can be taken out of the form after 2 or 3 days.
1. Start with a large bucket or an old mixing bowl with a 4L capacity. Measure out about 3kgs of sacked concrete and dump it into the bucket. Add cement (1/24th of 1cu. foot box). Mix thoroughly and break up any big clumps of material. Add about 170g of water to the mix, keep stirring by hand or with a spatula or trowel, always scraping the sides and bottom of the bucket. Gradually add more water until the consistency is like runny oatmeal.
2. Pour concrete into the form, but be careful not to dislodge the knockout. While pouring, smear concrete around the inside walls of the form and under the knockout to coat the surface with concrete. This will help minimise trapped air.
3. To help the air bubbles rise to the surface, vibrate the concrete by tapping the base of the form on the tabletop for a few minutes. Your final piece will always have some air bubbles if you're not using a commercial concrete vibrator. If you aren't getting results you like by vibrating by hand, you can try using an orbital hand sander and vibrating it against the form walls.
4. After the form is vibrated, wedge a piece of 0,5 cm foam under one side of the container so the top surface is level.
5. Smooth/trowel the surface with a plastic scraper. Take some time to remove excess concrete from the sides of the container, and get that top surface as smooth as you can (this will minimise sanding later).
6. Move the form carefully to a place where it can cure for up to two days. Cover with a plastic bag or painter's plastic drop sheet. This helps hold the heat and moisture in the concrete so it doesn't cure too quickly and crack. For this reason, do NOT place the concrete to cure in direct sunlight, keep it indoors or in the shade.
Step 4: De-moulding the concrete form
De-moulding is the when you remove the forming materials from the cured concrete. Sometimes the concrete can be removed without destroying the form, but in this case we're going to break away the plastic bit by bit. Any cuts you make through the plastic will scratch into the concrete, so be careful not to cut, pry, or gouge the concrete in any of the following steps!
1. Wearing rubber gloves and safety glasses, prepare to de-mould. Scrape excess concrete off the plastic form with a razor blade.
2. Start at the opening of the container, peeling back the plastic by hand and slicing down into it with a sharp razor blade.
3. Break plastic away by hand or with pliers. Remove a little bit at a time. Peel back, slice, and break away. Do this as carefully as possible, still taking care not to scratch or chip the concrete.
4. Be very careful when removing the bottom of the container. On each side of the form there is a tab. A small screwdriver or chisel and a quick tap from a hammer will help free those tabs.
5. After the plastic form has been removed, pry out the knockout with a flat screwdriver.
Step 5: Sand, grind and make the concrete iPad ledge
1. Flatten the base by sanding the bottom surface with a rough 120 grit hand-held diamond-polishing pad. Alternately use a belt sander and ideally a 12cm wet polisher with diamond pads suitable for concrete.
2. Using a hand saw, band saw, or tile saw, cut a ledge that fits in the groove created by the knockout. The easiest thing to do would be to start with a piece of wood that is the same thickness as the knockout, ½" (about 1cm) in this example. Softer woods will be easier to cut with hand tools if you don't have access to a band saw. You don't really need power tools for something like this.
3. Finish the concrete with sealer and wax before glueing the ledge in place with 2-part epoxy.
Images and info sourced from Instructables. To see the original version, click here.