No, you dont have to use any sort of adhesive. There is a tiny gap sometimes between the fascia and extension, but you can use 3M automotive double sided tape alond the top of the fascia where it contacts the bumper to make it fit perfectly with no gaps. The gap is barely noticeable, though. There are plastic tabs that run along the top of the fascia extensions that snap into place of where the stock front and rear valences used to be. Not hard to do at all