Form Footing - Inner EPS
Fill between the upper and lower inner Form-A-Drain with polystyrene.
Inner Form-a-drain filler strips
The 1.5" EPS is cut to 9-1/4" high for the inner Form-a-drain. Fit the 9-1/4" strips of polystyrene sheet between the inner Form-a-drain. Some trimming is needed when you have bulges due to Form-a-drain joins.
Between the inner Form-a-drain it is necessary to prevent the backfill drain rock and the filler polystyrene from falling out ahead of having the footing lining done. There are two ways of doing this dependent on the amount of space that there happens to be between the Form-A-Drain and the excavation soil. Where there happens to be enough space then glue an 11" tall piece of 2" EPS behind the 9.25" 1.5" EPS, ie use the same method as with the outer Form-A-Drain.
Sometimes where the excavation earth is tight you will not be able to pre-stick the sheets together and you will need to glue in place and use some creativity to get it to fit. Where there is room, use 2" EPS for the backing piece, but use 1.5" or 1" in places where there is less room.
Where there is not sufficient space then it is necessary to fix some thin plastic sheet between the upper and lower inner Form-a-drain on the inside of the footing trench. It should be a 1 foot wide strip cut from a 8'x4' sheet. Suitable sheeting is about 0.060" thick PVC (available from Lowes). Use self tapping screws on the top and bottom edges to attach the PVC sheet to the Form-a-drain.
It is necessary to remove any 2x4 spacer jigs that use U's on the lower Form-a-drain and replace them with straight bits of 2x4 that are 4'5" long.
(Typically the EPS between the outer Form-a-drain shown in the photo is added in a later step.)