1. Measure the box that will contain the tiles and mark the dimensions on a flat work surface. Arrange the tiles to fit within the dimensions, leaving 1/16- to 1/8-in. gaps between tiles and around the perimeter. (An alternative approach is to create the tile layout and then build a box to accommodate the finished design.) Use a tile saw (power or manual) or nippers to cut tiles to fit as necessary.
2. Once you’ve laid out the tiles, carefully cover them with strips of painter’s tape so you can lift them into the box as a group. (If you’re using a mixture of materials of varying thicknesses, you will instead need to “butter” each piece with the adhesive and place it individually into the box so you can selectively build up the heights of the thinner materials.) Before applying adhesive to the box, mask off the frame sides above the height of the tiles.
3. Apply adhesive using a 1/8-in.-notch trowel]; then set the sheet of tiles in the box and gently press them into the adhesive. Starting at one corner, hold down the tiles as you slowly peel off each strip of tape. Check the spacing between the tiles and adjust any that may have shifted during the transfer. Before the adhesive starts to set (in 15 to 20 minutes), clean residue from the tile fronts and any globs from between the tiles. (A toothpick works well.)
4. Allow the adhesive to dry for 48 hours before applying grout. Cover the top surfaces of any textured tiles with masking tape to keep grout from collecting in the cavities. To work grout into the joints, you can use a grout float, a rubber scraper or your fingers (protected by plastic gloves). Wipe across the entire surface with a damp (not wet) sponge to remove extra grout. Wait five minutes and gently clean the tiles again with a sponge. After a light haze forms (in about 15 minutes), buff the tiles with a soft rag. Wait a few days; then seal the grout.
Mosaic tiles (or tile scraps, stones, shells, broken pottery, etc.)
Wooden box (built or purchased)
Latex-modified thinset mortar
Unsanded grout (or sanded if gaps are wider than 1/8 in.)
Tile cutter and/or nippers
Grout float, rubber scraper or plastic gloves