There are many different ways to texture cement, including the conventional slick and broom finishes. Some things can be added to the concrete before or after it is poured, while other idea may require you to make wood forms or stamps that are depressed into the wet surface.
Step 1: Pebbles and Stones
Pebbles, stones, and coarse colored sand can be mixed into the concrete as you go. Measure out the mixture to keep it uniform from one batch to the next, but the ratio can be as high as 50% additive to 50% concrete mix. Substitute colored sand for ordinary builder's sand. After it has fully cured, clean the surface with Muriatic Acid. Another method is to scattered stones over the semi-wet surface, and squeegee them level with the concrete.
Step 2: Wooden Inlays
Use a jigsaw and cut little design out of wood or plastic. You can also purchase designs inlays at most hardware stores. Place the inlays as you want it to be, and tap the top of the inlay gently for a few minutes, encouraging the concrete to mold around the pattern. This method has the greatest potential, but it should be worked into slowly, starting with small, shallow imprints and than increasing the complexity as your experience grows.
Step 3: Sculpted Colonnades
Different sizes of PVC pipe are great for inwardly curving patterns on columns and supports. For example, split a piece of 2 inch PVC lengthwise, and press the outer curve into the wet concrete. Do this repeatedly around the column, forming a series of matching concave patterns. If the concrete will be coming out to sharp points, add 1/4 cup bonding agent for each bag of cement to give it more holding strength.
Step 4: Concrete Stamps
If you are experienced with a router, cut patterns into a piece of 1 inch plywood, and then use that design as a border for the concrete. Place the stamp carefully in place, and tap it gently with a rubber mallet. If you have a concrete vibrator available, touch the tip to the stamp, and then remove it. One example of a simple stamp is a square of plywood with a handle protruding from the top. Each time the ply is gently pressed into the wet concrete and removed, it will leave behind a different bit very similar pattern. This is a conventional method of texturing drywall ceilings, as well.
Step 5: Using Block-Outs
Instead of a solid slab, build wooden forms that fit within the main form. Pour the large area with a tinted cement, or one that has a special type of rock, and finish it. Remove the block-outs, and pour those with different color or textures, giving your complete slab a unique and original appearance. With block-outs, you can place complex shapes and patterns, as well as a variety of materials, within a slab so that it appears to be a solid pour.