When you shoot you trace forward and hit the surface. This gives you a possibility to start a custom hit event for each surface type. To add a new surface you need to open project settings and add a new surface (Picture 60). This type will show up after you reload the project. 

Picture 77- Surface types

After you created a new surface you can add a new row in DT_Impact data table. Choose your type in surface variable, in this data table you don’t have to fill every variable (Picture 78). 

Picture 78 - Impact data table

To give surface type to any object in the world you need to have physics material with your new surface type (Picture 79). This material you can initialize in any mesh actor in the world (Picture 80) or in the landscape layer (Picture 81). After you line trace to these actors - you will get hit information, where you can get physics material. In the physics material you can always get a surface type variable.

Picture - Surface type in physics material

Picture - Physics material in landscape layer

Picture - Physics material in mesh