Step 1: Gather Materials
You'll also need to gather a bunch of old crap to apply to your garden item. I am using old tile pieces, marbles, coffee mugs, broken flower pots, mirrors, and other odds and ends. Anything that will withstand the elements should be fine.
There are some tools and materials that you will need:
steel wool (or a scrubby sponge)
Thin set mortar
Tile snips (optional, for more fancy designs)
Glass cutting tool (optional, for more fancy designs)
Silicon adhesive (optional, for more fancy designs and for smaller pieces like a flower pot)
Step 2: Think About a Design...or Don't
I created a star template out of cardboard and traced it onto the birdbath with pencil. This keeps me on track when I'm applying the tiles.
Step 3: Break Stuff
If your design is somewhat intricate you'll want to break the tiles and mirrors with some degree of precision and accuracy. A glass cutter and tile snips come in handy here.
Glass cutter: a little, pen-like tool that has a sharp wheel to score glass. This will cost <$5 at a hardware store. You basically press firmly to score the glass. Then you tap the glass to break it along the scores.
Tile snips: These are like a hybrid between pliers and hedge trimmers. They gradually nibble away at ceramic tile to acheive a desired shape.
Since I am making a star pattern I had to make sure that I had some sharp, acute angles for the tips of the star. It is really important that you plan these things ahead. You don't want to be snipping away at tiles while your mortar is mixed.
If you're doing a free-form pattern then screw it and just break eveything with no regard.
Step 4: Prep the Surface
Step 5: Apply the "Intricate" Portion of the Mosaic Design
Apply the broken pieces to the object. Keep them pretty close together...1/8" or so. Any large gaps will use up expensive grout.
Step 6: Mix the Mortar
You'll need to get some tile thinset mortar at the hardware store. This stuff is pretty cheap (about $5 for 50lbs).
Mix it per the instructions with water in a bucket to get a paste-like consistency. Don't mix more than you can use is about 20 minutes or it will get too hard while you're working on it. It's better to make a few smaller batches than to waste a large one.
Note: if you are just doing a small object, like a flower pot, you can forgo the mortar. Instead use cheap silicon adhesive for all of the tile pieces. But for larger projects it is far more cost effective to use mortar.
You want the mortar to be like paste...not too runny but also not crumbly and dry. Keep in mind: It is always easier to add more water rather than to add more dry mortar.
Step 7: Apply the Motar to the Object
Step 8: Apply the Broken Pieces
Step 9: Let the Mortar Dry
Step 10: Grout the Mosaic
You want to keep the grout moving and smear it off the surface of the tiles and mirrors and stuff. There will be a glaze of grout left on the surface of the tiles that can be removed later but you don't want it to be so thick that you cannot get it off.
Use the sponge and the water to smooth out the grout and wipe the excess from the tiles.
Step 11: Let the Grout Dry
Step 12: Remove the Grout "Haze" and Seal the Grout
Let the grout dry and you can seal it. Sealing it is optional but it is a good idea because it will help keep the algae down and help it last longer in the winter*. The hardware store will have grout and tile sealer. You will probably only need one coat.
*If you use regular bathroom tiles, or any tiles that are not designed for outdoor use, you probably shouldn't leave it outside in the winter if it is cold where you are. The freeze/thaw cycles will cause the tiles to crack and chip off.