My kids and I had long wanted to play around with concrete and when we moved into our new house, I thought it was time for a concrete coffee table. I have to admit, when I made the table I didn’t have making an Instructable in mind, so my photos of making the base leave a little to the imagination. My apologies. Fortunately, the concrete top is pretty well documented.
Step 1: Building the Table Base
I decided to make the frame out of a cedar 2 x 4 and an armload of hardwood scraps, mostly to justify having moved them from the old house. First, I cut the cedar down to 1 x 2 strips. Then I cut the legs 18”, the cross-pieces 46”, and the side pieces 14”. I set my kids to work hand sanding these while I cut the hardwood slats for the storage deck. I had a mixture of pecan, oak, cherry, and black walnut scraps, so I cut 23 of them 1” square and added them to my kids sanding pile.
Step 2: Screwing It Together
Since I only had a handful of 3” deck screws on hand, and they were not exactly furniture grade, I decided to countersink the screw holes and hide the evidence with wood plugs. After the frame was together, I built the storage deck by randomly placing the mismatched wood types and spacing them 1” apart.
Step 3: Making the Concrete Form
To make the tabletop, I cut 1.5” strips of paneling to use as the sides of the concrete mold. I covered my worktable with a sheet of plexiglass and flipped the table base upside down on top of it to use as a guide. Next I hot-glued the paneling strips onto the plexiglass from the outside. I decided that I wanted an organic shape to the table, so I bowed the long edges by pushing the paneling strip until it looked about right, then glued it in place. After matching the bow of the second edge, I glued it down and removed the table base, leaving offcut blocks in the spaces where the legs would go. Finally, I put a layer of silicon caulk on the inside edges to smooth them and make them waterproof.
After preparing the concrete frame, I glued down a handful of agate slabs, various rocks I had cut on a tile saw, and a couple old filmstrip projector lenses to the plexiglass with a thin layer of silicon. Then I used a rag to apply a layer of wax to the whole inside of the mold, being careful not to get it on the backs of the insets.
Step 4: Prepping the Helpers
Finally, we were ready for the concrete! After explaining the do's and don'ts of working with concrete to my helpers (Don't taste it, throw it, or put it in your brother's hair! Do work fast! No taking a break until the concrete is smoothed out!), I gave them gloves and my daughter decided to wear my sunglasses for extra protection.
Step 5: Scooping the Concrete!
Continuing on the theme of using recycled materials, I used crushed glass from my city’s glass recycling program as aggregate rather than pebbles. I added some marble dust to lighten it up. We mixed up the concrete to oatmeal consistency and quickly scooped it in, working it in with our fingers to avoid air bubbles. (No pictures of this--we were using quickset concrete and were all too busy to take pictures!) When we were done, we pounded the work table with a mallet to dislodge any last bubbles, then screed the top back and forth with a flat board. Finally we covered it with plastic and left it to set.
Step 6: Polishing the Surface
Waiting until the next day was the hardest part. When we popped the form apart, the edges looked smooth! We slid it loose of the plexiglass and flipped it over. It looked great, so I carried it outside to polish it out. I borrowed a friend’s wet polisher and diamond buffing pads, then started the long process of buffing out the surface. I started with 200 grit and chose areas to highlight, then worked progressively down to 2000 grit. I wanted to have kind of a cosmic theme, so I just buffed sort of an S shape through the middle and left the outer edges less polished. After about three hours, it was done!
Step 7: All Done
The glass aggregate is beautiful and the agate slices turned out great—a big improvement over storing them for years in a box in my garage--but maybe the most exciting surprise was what happened to the projector lenses. The concrete cracked them as it set, but held all of the pieces in tightly, so they look kind of like dividing cells. After it dried, I sealed the surface with an aerosol grout sealer, then polished it with a coat of Howard Feed-N-Wax. So far it has kept a great finish and has been pretty stain resistant.
The table has been a great conversation piece, was a great project to do with the kids, and, if I win some equipment from the concrete contest, I’ll make a few more for friends.