Thank you so much to everyone who offered suggestions on how to mount large format prints. I successfully mounted the three photos and would not have been able to do it without the help from all of you. LULA rocks!
After carefully considering all the comments, here’s what I did:
I used the Lightroom export feature to size my prints to their final physical size in inches, 150 dpi, and sharpening for matte paper. I ordered low-cost prints from
www.posterprintshop.com, and specified matte finish and a 2” border, as I wanted room for error.
The comments about the flammability of polystyrene convinced me to abandon that idea. I next considered Masonite, but was concerned about the acidity of this product eventually yellowing the prints. Even thought my goal was not archival quality, I wanted to avoid anything that would obviously be a problem if at all possible. I finally settled on Gatorboard. It was more expensive, but it was also lightweight and easy to work with. I purchased three sheets of ½”x4’x8’ black Gatorboard locally ($83.34 each). I cut each sheet an inch larger in each dimension than the print w/borders. Again, not ever having done this, I wanted room for error, and that came free.
I was unable to find Gatorboard with adhesive available locally and the cost of shipping was prohibitive. So I purchased a 24” x 50’ roll of 3M568 Mounting Adhesive from Uline ($119.00 shipped).
At this point I was busy with another project that was higher priority so I had a week to worry and lie awake at night imagining all the ways this could go wrong. To make matters worse I had no time to try something different if it didn’t work, as a deadline was looming with no fudge factor built in. Fortunately it all went well. Here’s what I did…
Mounting Procedure: Note that I applied the adhesive first to the substrate, and not to the print, as suggested by the manufacturer. I did this because the recommended procedure would have been far too unwieldy for a print this size.
1) I prepared each print by unrolling it and letting it lie flat for a day. Then I rolled it up on a cardboard tube (I covered the outside of the tube with clean draft paper first to keep the print clean) with a strip of 24” wide draft paper lying in the middle on the face of the print, to protect the print when I unrolled it and pressed it into the Gatorboard. I rolled the print in the opposite direction from how I received it. This means the print face was facing inside the roll, and would allow me to unroll it face up. Being able to unroll the print in this fashion allows for a slow and controlled application of the print to the adhesive-covered substrate.
2) I then mounted the adhesive paper to the Gatorboard. This paper comes with protective paper on one side and the other side is slightly sticky. All of my prints were larger than 24” in the smallest dimension so it was necessary to lay down two strips of adhesive paper sided by side to cover the Gatorboard. I was greatly relieved to find that it was easier than I had feared to line the strips up so that there would be virtually no seam. I laid the slightly sticky side down, aligned the two strips, then used the provided plastic squeegee to press the paper firmly onto the Gatorboard, and finally used a razor blade to trim off the extra adhesive paper.
3) After all the adhesive paper was stuck to the Gatorboard, I proceeded to peel back the protective paper to expose the adhesive and discovered immediately that I needed to re-squeegee the paper so that the adhesive didn’t come up with the protective paper when I tried to pull it off. Doing that and pulling very slowly I was able to get it all off without any problems.
4) The next step required two helpers, one on either side of my work table, to hold the roll above the Gatorboard and slowly unroll it while I pressed the middle of the unrolling print onto the Gatorboard with my gloved hands. Since it was rolled up with some draft paper I was free to slide my hands around to ensure that it went down smoothly with no bubbles, etc. We unrolled about a foot of each print first, holding it away from the Gatorboard, so that I could do my best to align it properly before pressing it down, so it wouldn’t go off to one side as we unrolled it. Again, this was easier than I had feared. With the oversize Gatorboard and 2” margins I had plenty of room for slop, but ended up being off only about 1/8” over five feet. I think I was lucky and normally would expect to be off more than that.
5) I then went over the whole print with a laminate roller, working from the center out. Someone had commented to be careful not to press too hard and dimple the Gatorboard. Well I did that on the first print. Fortunately it's a small area and the print is mounted in a dimly lit room and it isn't noticeable. If you do this practice on some scrap Gatorboard first so you know what it takes to dimple it.
6) Next was trimming. I have a woodshop with a cabinet saw so this was easy. A high quality carbide blade went through the Gatorboard and paper like butter and left a very clean edge.
7) I didn’t varnish or otherwise protect the prints, primarily because I have no experience with this and didn’t want to ruin what was a good result so far. I may do it later after I’ve practiced on something smaller. The prints are mounted in a high-end restaurant and I don’t expect that there will be much of a problem with people touching them.
8 ) To address concerns about future warpage I decided to use the walls to hold the prints flat. I had a supply of aluminum French cleat material on hand so I epoxied a series of small cleats to the back of each print – on all sides and in the middle. I made a jig that registers to the edge of a print so I could install the cleats precisely and in a repeatable fashion. I then used a laser level on a tripod to mount the mating strips to the wall. I worked slowly and carefully and it took a little less than an hour to mount each print to the wall. The cleats hold the Gatorboard about a quarter inch off the wall.
Basically the entire process was easier than I’d expected and everything turned out well. I want to emphasize again that your responses to my post are what enabled me to get this project done. Note that what I ended up doing was quite different from my original plan. From your suggestions I determined that there were several methods that were likely much better than what I originally envisioned. Your willingness to take the time to contribute to the forum enabled me to formulate a mounting plan that was affordable, relatively easy, and worked out well. Thank you!