Measure the top of the picnic table to be tiled.
Measure and cut the concrete backer board to cover the tabletop uniformly.
Attach the concrete backer board to the tabletop using both tile adhesive and 3/4-inch wood screws evenly spaced along the surface about 10 to 12 inches apart. Using tile adhesive and wood screws will ensure that you have a secure and rigid surface on which to lay the tile.
Mark the center point of the tabletop. It's important to center the tile to get a uniform look.
Measure and mark lines on the tabletop to show tile placement. The possibilities are endless here depending on your choice of tile. Using a large tile in the middle of the table with smaller tiles to cover the tabletop edge and corners works well.
Dry fit all of your tiles on the marks making sure to allow for even grout joint lines. The thinner the grout joints in this application the better.
Measure and cut any tiles that need to be trimmed and place them in the dry-fitting process. Laying out all of the tiles without adhesive will enable you to make small adjustments as needed to create a great design.
Take a digital picture of the tabletop once you have dry fit and laid out the tile so that you can duplicate your design. (Skip this step if it is a simple layout.)
Post a large copy of the digital picture of your tabletop tile layout so that it is easy to see while you work.
Using a notched trowel, apply the tile adhesive to the concrete backer board surface. If it is a large table, do this in manageable sections so that the adhesive does not dry out.
Place the tiles on the table top according to the layout in the picture. Allow the tile adhesive to dry overnight.
Using a sponge-covered trowel, apply the sanded grout between the tiles, removing all excess grout as you work. Follow up with a wet sponge to remove the residual grout from the tile surface. Allow the grout to dry overnight.
Apply grout and tile sealant to cover the entire picnic tabletop and allow it to dry over night again. Apply a second coat of sealant to the entire surface to finish your new tile-top picnic table.