Squeeze a bead of glue along the short edges of the hardwood pieces that will abut the plywood. (Be sure to place glue on miter cuts.) Press edges along outside of perimeter of plywood, making certain miter cuts align. Hammer brads through hardwood into plywood. Wipe away any excess glue. Let glue dry. Prime the frame. Let dry.
Spread thinset onto surface of plywood with a notched trowel, and start setting tiles. (Use spacers if needed.) Let thinset dry overnight.
With grout float, spread grout over tiles, making sure to get grout between tiles. (Remove spacers if they’ve been used.)
Wipe away excess grout with a damp sponge, and let dry for 1 hour.
Paint frame: Use painters’ tape on tiles to protect them while you paint. Cover perimeter of tiles with tape, and paint the hardwood. Let dry.
2 pieces of 1 1/2-by-1/2-inch hardwood, such as poplar, miter-cut to be 8 3/4 inches on one side and 9 3/4 inches on the other
2 pieces of 1 1/2-by-1/2-inch hardwood, such as poplar, miter-cut to be 14 1/2 inches on one side and 15 1/2 inches on the other
1 piece of 3/4-inch plywood, cut 8 3/4 by 14 1/2 inches
Tile trowel (tiles' packaging will specify what size is required)