Outdoor Concrete Coffee Table

This instructable will show you how to make a great outdoor side table that will never, ever, move in the wind. I made this for my construction and design class. Ensure you wear the proper PPE. Please read all the instructions before starting this project. This design isn't perfect and may have issues you'll need to address.

Tools

1. Angle grinder
2. Ruler
3. Sharpie
4. Linisher
5. Set Square
6. Metal cutoff saw
7. Flat bar bending machine
8. Welder
9. Vice
10. Milling machine (optional)
11. Drop saw
12. Band saw
13. Drill bits (6mm, 13mm)
14. Orbital sander

Materials - Internal structure

1. 12 mm threaded rod
2. 1000 mm metal band
3. 12mm nuts x3

Materials - Legs

1. 25 x 25 mm treated wood
2. 8mm dowels x3

Materials - Concrete (not approximate)

1. Aggregate
2. 10 kg easy-mix concrete

Testing the materials was crucial for the success of this side table (obviously, you don't need to do this). I tested the concrete-to-water ratio and aggregate embedding techniques. I additionally tested different joint connections. The reason for my decision to use lapped dowel joints and weld the internal supports is that these joints are simple to make and easy to cut at the right angle, providing the strength needed for my side table. The other joints I tried were too complicated, as was the case for the angled dovetail, or would lack the necessary strength, like the mortise and tenon. The feedback received from whānau has told me that the dowelled lap joint is aesthetically pleasing and would tie in nicely with the area where the side table is going to be located. For my internal supports, I have decided to weld them together. My reasoning for this is that it will add necessary structural support for the concrete top. Additionally, welding has proven to be a skill that is relatively simple and extremely strong.

1. Begin by measuring your threaded rod into 3 240mm lengths. Cut these on your metal saw of choice; I used a metal cutoff saw.
2. Cut your flat bar to a length of 1600mm. This will create a circle that has a circumference of 400mm.
3. Cut out 6 lengths of flat bar at the measurements shown in the photo. These will be where our legs connect.
4. Cut 3 pieces of flat bar 60mm long.
5. Smooth all sharp edges out on the linisher or an angle grinder

This step is rather simple. I used a flat bar bender to gradually bend my length of metal into a full circle. Keeping the metal straight was a little difficult and was something I had to overcome by changing the direction I was bending the metal. Once you have completed the step, both sides of your metal should meet one another.

This is one of my first times welding, so make any changes you think are necessary

1. After applying the appropriate PPE, begin by welding the three pieces shown in photo one together at their edges. This means that the parts welded onto them would all be at the same distance and placement. We will call this piece the triangle.
2. First, tack and then fully weld the pointed metal pieces on top of these pieces at 90 degrees, as shown in photo 4.
3. Insert the threaded rod through the hole you have made in the metal band and align them together in the middle. Tack all sides together, ensuring they are completely flat. You may need to prop up the rod with some scrap metal. Weld these parts together and weld the points where the threaded rods and metal band meet.
4. Align the triangle in the middle of the threaded rod, as shown in photo 4. Weld these parts together from the bottom. (You may need to do this step upside down to properly weld the pieces together.)

1. Cut 6 lengths of 400mm.
2. Angles are very important, so make sure you are using the same measurements shown in images 5 and 6.
3. Cut angles as shown in the diagrams. This can get confusing, so make sure you do everything the same for all 3 legs.
4. Cut a jig piece from scrap wood to drill holes in the outer legs. This jig should have an angle of 13 degrees.
5. Drill a 26 mm hole with a spade bit 20 mm deep, 280 mm up the wood, while using the jig as shown in photo 2.
6. Drill a 12 mm hole in the centre of the hole you just drilled. This will be where the legs connect to the exposed threaded rod.
7. Glue the lapped joints together with wood glue and embed the dowel.

This part can be significantly improved from the method given. I have tried to include some of these improvements in the upcoming steps.

1. Measure and drill 3 holes where the rods will stick out. Looking back, cutting the bucket flush with how thick the concrete was going to be may have been the most effective way to help this concrete process work smoothly.
2. Make small incisions above 2 of these holes to help force the internal support into the bucket.
3. Insert the internal supports and put the nuts on loosely. This should help the bucket deform less.
4. Tape over exposed cuts.
5. Scatter the coloured stones at the bottom of the bucket.
6. Mix around 13 kg's of concrete following the measurements shown on the bag. (I mixed this in a small bucket, and that wasn't the best. I recommend a large bucket or a proper concrete mixer.
7. Pour the concrete slowly; try to get an even coat without any air bubbles. Gently tap the exposed rods, as this will help vibrate the air bubbles out.
8. Smoothen with a trowel.

1. Remove the concrete from the mould after it has partially cured. I left mine for 3 days. The bucket will be unusable to avoid damaging the concrete.
2. Use a wire-brush attachment on your drill and start by slowly removing the concrete surface. This should begin to expose the coloured stones. Make sure you do this in a well-ventilated area with the proper PPE, as concrete dust is toxic.
3. Don't take off too much; you can always remove more.

If your concrete came out anything like mine, there will be some bumps that need to be removed.

1. Use a cold chisel to remove bumps. (Make sure to wear eye protection, as this may result in debris flying off.)
2. Coat the concrete with polyurethane of your choice. (I won't recommend one because it has started to chip.) This coating should lock in the exposed aggregate and keep stones from falling out.

I trialled several stains for the legs of this side table and decided on the darkest wood stain I could get my hands on. This is because the side table is near some planter boxes of a similar colour. Additionally, this covered the green tinge of the treated wood. I applied this coating with a rag and did 2 coats.

This step is rather straightforward, and it helps to have a helping hand. Turn the tabletop upside down on an elevated surface. This will make putting on the legs with their overhang much easier. Attach the legs with their mounts and screw in the nuts. Make sure to fully install one leg before moving on to the next leg. This will make the installation much easier because it can be a tight fit.

Well done, you have completed this project and built an outdoor side table! I hope you have enjoyed making this table, and let me know how it has gone.