First of all I needed to cast up a couple of blank plaster plaques to fit onto the resin plinth I had chosen. One will form the pavement the other a wall.
I began by rolling out some plasticine to an even thickness. To do this I used a couple of pieces of balsa wood and a wooden dowel. While it isn't essential to have the plasticine all of an even thickness it does help to achieve a better result.
Using a straight edge and a scalpel (or craft knife) I cut the plasticine into four strips.
Using a piece of plasticard as a base and my plinth as a guide. I built a mold using the plasticine strips. Place the cut edges of the plasticine against the sides of the plinth one at a time and gently press them into place.
Mix up your plaster as per the instructions and (on a level surface) carefully pour into the mold to the required thickness.
Once the plaster has set (be patient & dont poke it!) carefully peel away the plasticine and the plaster plaque should pop free of the plasticard. Now let the plaster dry out over night. Depending on the thickness set plaster can take a long time to fully dry out. Although you can carve it when slightly damp I'd recommend that you make sure it's fully dry before you do any gluing or painting.
The plaster plaque probably won't be perfect so carefully sand the edges to remove any flash. I then began to inscribe a brick pattern onto the plaster using a pointed stylus (in this case a piece of brass wire filed to a blunt point).
With the basic brick pattern inscribed I then added some texture and damage using a variety of tools. A stiff paintbrush is particularly useful for softening out some of the hard edges. To get an overall rough texture I placed a piece of course sandpaper rough side against the plaster and burnished it. The texture was then impressed into the plaster. I used a stone out of the garden as a texture stamp to create some random looking chips and dents.
It's well worth casting up a few spare plaques and trying out a variety of tools and techniques as a wide variety of finishes could be easily created.
Working with plaster can be a very messy business and sanding/carving plaster will create a lot of dust. Don't forget to follow all the usual safety precautions to protect your eyes and lungs.