Working with concrete is fun. You can cast anything in concrete, provided you have the right tools, materials and the know-how.
Here is a step-by-step Instructable to make a small Bedside Coffee Table in concrete, with easily available materials and tools at home. You can also find some tips on working with cement and concrete here.
Step 1: What You Need
We do not need any special equipment or form work to make this small coffee table. I have used equipment and tools commonly available in any household. I have purchased an one kilogram packet of white cement and borrowed small quantity of sand from a neighbor.
I have divided casting work of this table in three parts: The Base, the middle section and the top section.
Molds (Form work):
- A small bowl from the kitchen for the base
- An empty glass bottle for the mid section
- An ornamental plate for the top section, also from the kitchen
Poach the bowl and the plate from the kitchen, as I did, without anybody noticing them as missing and return them back after three or four days. Of course, the glass bottle is expendable...
- One kilogram packet of White Cement
- About half a cubic foot of clean river sand
- Clean water
- Little quantity of oil for lubricating the form work (the molds). I have used Coconut oil. You can use any oil.
Other equipment borrowed from the kitchen:
- A medium sized pan for mixing
- A ladle for mixing the concrete
- A small bowl for water
Step 2: Lubricate the Molds
Lubricate the Molds...
Apply any oil liberally over the surface of molds and form work which will be in contact with concrete. Without mold release, you can not take out the concrete from the molds without damaging your piece of concrete or the mold.
Here I have used coconut oil and applied it using a small piece of cloth. For the bottle, I have poured some oil inside, rolled it so that it covers entire inside surface of the bottle and then drained out the excess oil.
Step 3: Make the Dry Mix
The first step is to measure the dry materials required for the concrete work and mix them well uniformly. Here I have used coarse sand and white cement for the concrete. Technically speaking, this mix is known as "Cement Mortar", but the work being very small in nature, I have not added any stone aggregates to the mix, instead used coarse sand, which contains lots of coarser particles. Do not use 'only cement' for any of your work as this does not have any strength and will form cracks in a few days time.
What is the proportion of Cement and Sand...?
Cement and sand are added in proportions of 1:3, 1:4, 1:6 and so on, 1 part being cement and 3,4 and 6 being sand. Less sand in the mix is considered to be richer and higher in strength and quality.
I have used cement and sand in the proportion of 1:3 for the coffee table.
How do you know the exact quantities of raw material required..?
Cement acts as a binding agent and fills the voids in the final mix. The part played by cement in increase of volume in the mix is very negligible. So, take sand equal to the volume of concrete you are going to pour and then add little more.
For example, here for casting the base in the small bowl, I have measured the sand in the bowl itself to its full capacity, added little more sand and then measured one third quantity of white cement. This will cover the concrete requirement for the base. For the middle and top sections, take materials accordingly. Roughly speaking, you need about 1.20 to 1.25 cubic feet of sand / aggregate for 1 cubic feet of concrete.
Step 4: Mixing the Concrete With Water
Now add water in small quantities and mix well. The final mix should be uniform without any lumps and also without any excess water. Correct amount of water in the concrete helps in keeping the strength of the final product as well makes it easy in handling and compacting the concrete, known as 'Workability of Concrete'.
Step 5: Concreting and Curing
As our molds and concrete are ready we can start pouring the concrete in the respective molds. Pour in layers and work with the ladle so that no air bubbles are trapped inside. For concreting in the bottle, use a small stick to compact layers of concrete inside. The concrete starts setting after 30 minutes. So, you need to finish the concreting of all sections within 30 minutes after mixing with water.
After about 10 to 15 minutes, you can find a layer of water with some cement slurry forming on top. Using some old news papers, sponge out the excess water on top. This will help in having a well finished surface.
Now leave the molds with concrete undisturbed for about 24 hours in a safe place. After 24 hours, submerge all the molds in water for about three days for curing.
What is Curing and why three days submerged in water...?
When cement comes in contact with water, a chemical reaction takes place and temperature of the concrete starts increasing. Curing is the process of cooling down the concrete. Concrete sets down well in 24 hours, so it is safe to submerge them in water without any damage.
All concrete works attain 50% of their designed strength in three days time and the full design strength is achieved in 28 days. After three days of curing, you can safely remove them from the molds without chipping any edges
Step 6: Demolding
After three days of curing, take out the molds from the water. Invert the molds over old news paper and tap them lightly. The concreted section will slid out of the mold easily. Break the glass to remove the mid section from the mold and dispose off the broken glass pieces safely. Take care while breaking the glass as the chances of cutting yourself with fragmented glass pieces is more.
Now we got all three pieces of finished sections with us, which needs to be glued together. You can wash and safely return back the bowl and the plate to the kitchen, which nobody noticed as missing for four days in my case.
Step 7: Finishing
Mark the centers of top section and bottom section, where the mid section will be glued down. Apply an epoxy based adhesive like Araldite or Gorilla Glue. These adhesives comes in two parts, Resin and Hardener. Mix well and apply over the concrete surface and stick the pieces together. Leave it undisturbed for about 24 hours.
Your small Bedside coffee table is ready...
Step 8: Epilogue
Hope you all enjoyed making this small coffee table with available house-hold items. The total cost of this project works out to less than a Dollar as I have purchased only one kilogram of white cement.
Some Safety Notes:
- Dry cement dust contain very ultrafine silica fume particles. Avoid inhaling the cement dust. Use a mask while working with cement.
- If you happen to handle cement concrete by hand, use hand gloves.
Enjoy your Bedside Coffee on this concrete table...!!!