Using 2"x4"s and 2"x6"s to make forms for the wall cap we plan to give it the appearance of thick slate on top of the wall. I looked into buying real slate caps; Pennsylvania Brownstone (I wanted a very traditional look as our house is 150 years old). I knew real slate would be expensive but was shocked at how much it would have cost (basically the cost of our entire project). So we will pour concrete and finish it to look like slate instead.
Start off by connecting the lip of the cap (2"x4"s) with masonry screws to the concrete wall. This will provide a base for you to connect the outside of the form. Screws are placed about every 8 to 10 inches. You can do this by taking the impact drill again with long a masonry bit and predrilling through the wood and concrete. Then screw the wood flush to the wall.
Then we used 2"x6"s to create the outside of the form. These too were connected by screwing through the lip and into the concrete using 6" long masonry screws. Again, this was done with the impact drill and screw gun as above.
You must check that you are staying level with all the forms, as the concrete will be poured to the top of the 2"x6". If they were not level it would be seen in the wall cap itself.