Hello Jake!
You can use the Pre Installed Concrete Material "Surf Poured Concrete".
If you are new to ArchiCAD, here is a good way to make a new material. (This is done in AC12)
Find a good picture of a Concrete Wall on internet. Save it as a JPG File.
Load the material in Library Manager by dragging it from the left to the right in the Library Box and click "Done". Go to
Options/Element Attributes/Materials
. Duplicate the material that is closest to what you want to create, here "Surf Poured Concrete". Search for the material you just loaded into the Library.
In the end, go to "LightWorks Rendering Engine" and click on "Match with internal engine" to ensure your rederings will have the right picture.
Good Luck!
Ingolf Sundfør, Bricklayer, Author of several Real Life Problem Solving Books for Archicaddicts in Norway.
PC/i7/W11/ArchiCAD 6.5-27