I has a mantle that is getting prefinished and I do not want to have any nail holes in the mantle after it is finished. I am looking for a glue/construction adhesive that sets up within a few minutes that I can just hold it in place while it sets. It is going against drywall. I have a 3M industrial glue gun that I was thinking about maybe using and have some confidence in, but I can just picture the customers face as I hot glue their mantle to the wall.... Maybe a two-part system?
From contributor Le
Not something I'd take to chance. You are relying on the paper facing of the drywall to hold the mantle up. I'd figure out a mechanical fastener technique that could hold the mantle up. Without seeing the mantle it's hard to design it. I usually leave the crown molding off and the installer can screw through the backer and then place the crown on the mantle and use 23 ga nails to attach the crown. If you use glue on the crown then the 23 ga nails can be minimal, used as clamps until the glue dries.
If you are hellbent on using adhesive then use a normal construction adhesive and hot melt glue. The hot melt will hold it temporarily until the construction adhesive sets up. Just warn then not to put anything on the mantle for a few days.