New shower install: Mortar vs felt pad.

I am installing a new Sterling Accord shower, about 3' X 5' base. Directions said to install the felt pad underneath the base but there was no pad included, as I see others have also experienced. Viewing Sterling's instruction videos it appears that I could substitute roofing felt (tar paper) or use mortar.

Again watching Sterling's instruction video it appears that the mortar is not mixed with water... just put in dry. Is that correct? If the mortar is mixed with water... the video did not indicate it was troweled smooth but put in rough. Your assistance is greatly appreciated!

Thanks for your valuable service!!!

Ron

Set 10-12 small piles of mortar, and then set the base down straight on top of the piles so that the piles "squish" into the bottom honeycomb. Don't use too much water in the mix, you want the piles to be stiff yet "squishable".