To Make a Coaster or Trivet from a Broken Glass Bottle, you have to Place a ceramic coaster or trivet onto a sheet of newspaper. After that, spread a 1/8-inch thick layer of fine mortar over the top of the coaster or trivet with using a small trowel. Then, Press colorful broken glass into the mortar. You need to position the glass pieces so that the sharp edges are pressed firmly into the mortar. You must allow the mortar to set and dry for six to eight hours.
Next, spread a 1/8-inch thick layer of fine grout over the entire top of the coaster or trivet using the trowel. Forth, Wipe off the excess grout from the top of each glass piece using a damp sponge. You should allow the grout to set and dry for an additional six to eight hours. After that, apply a layer of clear masonry sealant over the entire top of the coaster or trivet and allow the sealant to dry for four to six hours before using it.