You have to be careful of the types of adhesive you use on composite.
Some adhesives, particularly two-part adhesives really heat up when curing.
Certain makes and qualities of composite will react to this high heat temperatures in concentrated areas causing dimpling visible on the face of the sign. Not all glues do this, nor all composites do it. but i would advise testing whatever brands and grades of composite you are using on your composite before doing a live job.
I use a 3M two part adhesive which you can by from various sources, such as Amari. I dont know the codes off hand to give you sorry. even if you buy this, check its compatible with the brand/type composite you use.