Digital BW, The Print

Being a photographer (an a woodworker too) this "tacking" question relates a lot whit what we call "surface tension". Any substrate used will warp if only one side is coated; using a 3' x 6' (and 1 1/4" thick) wood panel, if only one side is glued, let's say with Arborite, you will see the warping. It can takes a week or a year depending on the conditions but… it will warp.

If you want to test some substrate. I would consider gluing a scrap piece of the same material on the back of the mounting board to alleviate the effect. That's why you see furniture (made with Arborite for example) having a "backside" glued with a similar material to stop the warping.

Good luck