Step 1: Tools and Materials
lots of newspaper,
an old sleeping pad,
cement mortar (thick form of plaster),
lots of tiles (for the mosaic),
an old piece of cloth,
plastic buckets (for mixing compound, adhesive and mortar),
Step 2: The Structure
First of all, you have to think about the sculpture's shape. You can choose nearly anything here (e.g. an animal, something surreal or even a humanlike figure), you just have to consider that the less compact it gets the more complex and difficult it is to realize. Also, cement mortar is not the best material for precise and fragile works.
I've decided to make a shell.
When you have decided for a shape, you first start by buliding the sculpture's wireframe -model out of chicken wire. The interior should be filled with newspaper and/or an old sleeping pad (so the mortar won't fall through the wire). Furthermore you should insert some bent metal rods so it will withstand the weight of the mortar.
For the shell I only had to make a round ball for the base structure. Tie the ends together with some leftover wire.
If you want to go for a human figure or something else that's not very compact, you will need to strengthen your frame by adding more thick metal rods, particularly in the rather thin areas of your sculpture.
Step 3: Adding Plaster
I used a ratio of 3:1 mortar to water (about the same as if you build a house)
In a first step I added mortar to the top half of the sculpture. The technique for applying the mortar is to take some with your trowel and literally throw it onto the sculpture. If you do it right, it will stick to the wireframe in an uniform layer.
After I had finished the top half, I let it dry until the next day and then did the lower half.
I let the mortar ball dry for another day (unfortunately I have no pics of the ball).
The next day, I started to add the basic shell structure on top of the ball. In the first pic you can see darker structure (still wet) on top of the brighter ball (already dried since the day before).
When you have your desired form, you can carve away some mortar to get all the details (second pic).
The third pic shows the shell on the next day, completely dried.
Step 4: Laying Out the Mosaic
Take some old tiles wrap them in an OLD piece of cloth and relieve all your stress with a big fat hammer:-D
continue this process until you have the desired size for your mosaic tiles.
If you want to have smooth edges on your tiles you can put them into a concrete mixer together some water and spin it around a few times.
Next you have to mix the tile adhesive according to its instructions. Don't make too much at once, as it will dry rather quickly and laying out the mosaic is usually not a very speedy task;-)
When laying out the tiles take care to have an uniform height! Otherwise it will be pretty difficult to add the joint compound.
When you have finished laying the mosaic, you can mix the joint compound according to its instructions. Apply the compound with your trowel (but don't throw it this time;-)). Take some compound onto your trowel and spread it onto the surface. Take care to get enough compound into the gaps, so that there're no holes left.
When you've finished applying the compound take a (not drippinng) wet sponge and remove the surplus compound. Now you have to let it dry for a few hours. After about half an hour a white film (or the color of your compound) will start to show up on the tiles. Just take a lightly wet sponge (it must be clean water!!!) and rub it away carefully (you may have to repeat this step quiet often).
Et voilà: you have your own unique garden sculpture!