Several years ago, I purchased a Drytac 26" laminator, and drove to Toronto for a day of training on facemounting. I was printing on a 24" HP Designjet 130nr printer at the time, and learned that the best results would be had from the smoothest possible surface, so I standardized on HP Premium Plus Photo Gloss paper for facemounting using Drytac Facemount, "an optically clear pressure-sensitive mounting adhesive protected on each side by a clear polyester release liner." With rigorous attention to detail, I learned to facemount 24 x 36" prints on 1/8" plexi and Dibond, and adhered aluminum braces to the back of the Dibond to stiffen the straighten the print, and provide a support for hanging the work. The mounted prints looked pretty good, but I was always bothered by the inevitable silvering that was most visible in the dark areas, an effect which is completely absent in Diasec mounting using the silicone adhesive.
To my chagrin, after a year or two, I started to see the aluminum bracing structure telegraph through to the image side of the print with an effect like accelerated silvering. At that point, I switched to having Laumont Studio (NYC) do all my large facemounted pieces, and they have always done an excellent job. In working with Laumont, I learned that Diasec (the process they use), is chemically incompatible with inkjet prints, so I was also forced to let them produce C-prints on their Lambda printer. This was somewhat unfortunate, as the Lambda simply does not have the D-max and color gamut of modern inkjet printers. Even though they supplied me with their printer profiles, and I used Jeff Schewe's method of soft-proofing with final adjustment layers for punching black and tweaking contrast and saturation, the C-prints were always a bit disappointing in comparison with my HP proofs.
More recently, I purchased a Canon iPF8100, a 44" 12-color pigment printer that produces substantially more beautiful prints than the Designjet ever did, prints which are in a completely different league than the Lightjet or Lambda. Knowing that these prints should not be facemounted, I have switched display tactics, and moved to using the gorgeous welded and powdercoated aluminum frames that Smallcorp builds (and which Laumont also distributes). http://www.smallcorp.com/aluminum.html
I still mount my prints on Dibond and brace them with aluminum, but by putting them in a Smallcorp shadowbox frame, I solve several problems at once: I can have the best possible print, I can protect that print from dirt and damage, and if the plexiglas ever gets scratched, it can easily be replaced.