In our house, we are avid recyclers and separate the rubbish. I also pick up PET bottles and aluminum cans whenever I take the dog for a walk (see 'Dog walkers clean streets' on FB). All plastic bottle caps are put to one side. These used to go to a charity, but that outlet has closed down. So now they are used to create art.
I have two garden coffee tables with a broken webbing surface. A temporary wooden frame the size of the coffee table was made. The plastic caps were arranged face-down inside the wooden frame on a flat surface (so that the final surface of the coffee table would be flat). With all the caps in place, tile glue was used to fill and cover the back of the caps. A square of thin aluminum sheet was cut to size and placed on top of the tile glue with some added weights while it dried.
When the tile glue was dry, the wooden frame was removed, and the assembly was inverted so the caps were the surface and the aluminum sheet was the base. Right angle aluminum edging (reclaimed of course) was added to provide strength and a neat finish. Finally, tile grout was used to fill in the gaps between the plastic caps and finish the surface. The new table top was then fitted to the frame of the old coffee tables.
Lessons learned: for the next table I may rethink the idea of using the tile glue, as it meant the final table top was cumbersome and prone to cracking. I had to use a lot to fill all the caps and add sufficient depth to cover all the caps. Also, in the end, the aluminum sheet did not stick to the tile glue, so I had to use a "no nails" glue gun to fix it in place. Next time I might only use "no nails" glue from the start to stick down the caps. But this will require using caps of all the same depth to get a flat tabletop surface. This next project will follow quite soon...