I find that puzzles mounted in sections are easier to handle, mount, and hang, and could also be more easily stored, allowing you to rotate out your puzzle collection on your walls. This also allows the weight of each section to be supported individually, which should reduce the chance of buckling over time, although I haven't had any puzzles hung for very long with this method.
I recommend reading through the whole process since I had a few lessons learned along the way, and it would be good for you to understand the whole process before beginning. If you have any questions, feel free to comment!
First-timers may want to try out the 3M adhesive on a 1000 or 2000 piece puzzle first such that only one piece of foam board is needed. For an example of that, you can follow my mounting of the 1000 piece Tiger Photomosaic in this post. When creating panels for the first time, you may want to try the simpler step 5b instead of step 5a below, but after that you'll probably have the hang of it.
You can read about other mounting projects here.
1. Foam board(s) to fit the size of your puzzle
2. 3M 568 Positionable Mounting Adhesive (squeegee and protective sheet included)
3. X-acto knife or utility knife
4. Colored duct tape of your choice (optional) to wrap the edges of the foam boards
5. Yard stick or straight edge
6. Pen or pencil
7. Wax paper
9. Rolling pin (not pictured)
10. Cutting mat or flattened cardboard box
11. Command picture hanging strips or frame
12. Level (or level app on your phone)
This method uses a straight edge along the gap between the panels. This makes the gap larger which doesn't support the pieces along the gap as well, but is a good option for first-timers. To follow this option, use step 5b instead of step 5a.
Option 2: Advanced method
This method uses a "toothed" pattern along the gap between the panels in order to better support those pieces. It can be a bit tedious but I found it to be worth the extra patience.
Step 1: Prepare your surface
You will want a flat, stable, clean surface which is large enough for your entire puzzle to be assembled as one piece, even if that's a floor.
Step 2: Measure the actual puzzle and foam boards
I had to insert this step when I hit what is now step 6 and found that four 20" x 30" foam boards were just a bit too small because the actual puzzle is 60 3/8" x 40 1/8" and the foam boards were just shy of 20" x 30". Therefore the smaller gap that I wanted with the nice toothed lines I drew below wasn't going to work. Lessons learned!
During the assembly I was using some 30" x 40" foam boards that I had cut down to 24" x 36" to fit by 48" x 72" work space. I decided to just cut these down more and use them instead of the too-small 20" x 30" ones.
Step 3: Select the foam boards you will mount the puzzle on
When I mounted African Animals, I used 3/8" thick foam boards since I had encountered a lot of 3/16" foam boards that I couldn't tell were slightly warped until I got them home. However on this puzzle I'll be using 3/16" since it may end up in a frame. To check for warping I hold them up against a table or wall, since apparently my eye isn't good enough. Be sure to flip it and check both sides!
You'll also want to avoid boards with any dimples (right), as pieces may not adhere well to these areas. Dimples on the side which won't face the puzzle are okay. If you won't have much scrap to cut off of the edges, you'll want to make sure that the boards you select don't have any bent or dented corners. I'm not sure if it matters, but so far I have always adhered to the side of the foam board without the label.
Step 4: Flip the puzzle + lay down wax paper
When I flipped African Animals to mount it, I split it into fourths first, and had a mishap when flipping one of the sections, so I ended up partially reassembling 1/4 of the puzzle. This time I was more cautious and first split it into quarters, then those sections into quarters, flipping 1/16 of the puzzle at a time by sandwiching it between two foam boards. It took longer, but I didn't have any issues, so it was worth it!
The adhesive won't really stick to wax paper, so it will protect your surface and keep the adhesive intact if the two come in contact. I wasn't thinking ahead an didn't end up laying down wax paper until between steps 7 and 8. As an afterthought, it can be hard to get the wax paper under the puzzle, especially if it has a loose fit.
What I will do next time is lay out the wax paper on the table before I flip the sections onto it. I would recommend trying this. Either way I think it's easier to tape the sections of wax paper together since they like to slide around. I also taped the wax paper to my puzzle table.
Step 5: Mark the seams
If you're mounting your puzzle in sections or panels, you'll want to decide where your seams will be, which will be at least partly dictated by the size of your foam boards. In this case, I am splitting it into four equal quadrants. When mounting in sections, there needs to be a gap between the pieces of foam board so that the peg from one side can pass behind the hole from the other side when the panels are separated.
When I mounted African Animals, I made the gaps in between each section straight edges. This was easy but didn't support the pieces along those gaps as well as it could have. I decided that on this one I would try a "toothed" edge along the gap in order to support the pieces along the center edges. If you could like to follow this method, follow step 5a below. If you would like to follow the simpler straight-edge method, follow step 5b below. First-timers may want to go with 5b the first time around.
Step 5a: More time consuming but better support for gap edge pieces
For this method I outlined where I wanted to cut, in a toothed pattern which leaves a gap for the peg from one side to pass behind the hole from the other side, while supporting the edge pieces as much as possible. This method can be a bit tedious, but I found the result to be worth it.
First mark your seams in one direction, then the other.
This is where the four pieces of foam board will meet in the center.
With the straight-edge gaps I used in African Animals, the pieces along the gap only have the support of the foam board behind half of the piece. This means that you need to be gentle with those edges when handling the sections. To follow this method, refer to the mounting of African Animals.
Step 6: Cut the foam boards
I like to choose the "nicest" corner on each piece and make those face the outer corners, while adhering the side without the label to the puzzle. Trim any excess, then you'll need to cut a toothed pattern if you followed step by 5a above, or stick with a straight edge if you followed step 5b.
Step 6a: Cut the foam boards to size
You'll want to measure the length between the gap and the edge of the puzzle in both directions for each panel or quadrant of the puzzle, and use this as your foam board size. This is where you can also choose to have the nicest corner and edges face the outside edges, although if you're going to be wrapping the edges in tape, then they don't need to be perfect.
If you're wrapping the edges with tape, the size of the boards needs to be exact, since you'll need to wrap the edges before adhering the foam boards to the puzzle. If you aren't wrapping the edges, you can leave a little extra foam board around the edges and trim it off later. I recommend using a straight edge to mark your foam boards and cutting based on that, instead of trying to use the outline of the puzzle. Here I also label each foam board "top right", "bottom right" etc. since this will matter when cutting the toothed pattern along the gap edges.
I didn't realize until I started taping the edges that I forgot to close the gap at the edges so that it's less obvious that the puzzle is in multiple sections from the side. However with the toothed method, the gap turned out to be so small that it's hardly noticeable.
Skip this step if you're doing the simpler straight edge along the gap. I find that a finer X-acto knife works better for this step than a thicker utility knife. What worked for me was to line up the foam board and the push it back a bit so I could see the lines, and then score the board according to the toothed pattern.
When you're done cutting the boards, it will look something like this:
This step is optional but I feel that it gives the edges a more polished look if you aren't going to be using a frame.
I recommend using a single piece for each foam board, wrapping it around the outer corner as well as the other 2 corners that are along the gaps. Smooth it down along the edge as you go, but don't fold it down yet.
At the corners, make a slit above and below the foam board, but leave the tape that's touching the edge intact. This includes the 2 corners along the gaps in addition to the outer corner.
All of the edges taped:
Since on this puzzle I used the toothed pattern along the gaps to provide more coverage, at first I couldn't decide whether to make the gap in the adhesive narrower and cover the toothed area, wider and leave that area uncovered (but still supported by the foam boards), or follow the toothed pattern with the adhesive. I decided to go with the narrower gap since I figured the adhesive would stick anyway if I tried to follow the toothed pattern. See step 12 for steps learned later on this.
Move your foam boards to the side for now and get out the adhesive. You'll want to leave your gaps uncovered with the adhesive as you do this step. Try to only touch the edges of the adhesive so that your fingers don't remove any, but if you do get some on your fingers, it comes off easily. I usually place the end down first and roll it out from there. I like to start at the gap and work towards the edge. Slowly roll it out and don't worry about cutting it yet. Place it down very lightly for now, and if you need a few tries to align it properly, it comes back up really easy without leaving anything behind if it's been placed lightly. Once you like where you have it, lightly smooth it down with your hand. The bond will not be permanent during this step.
Using the supplied squeegee, apply firm pressure in horizontal, vertical, and diagonal directions over the whole puzzle, then go over the edges and gaps again. You want to keep the squeegee perpendicular to the puzzle as you apply pressure. Applying pressure activates the adhesive and makes the adhesive's bond permanent, but it won't be permanent until you also apply pressure to the front.
Step 10: Peel off the backing paper
Only peel off the backing paper for one panel, then move to step 11. I like to start at a corner. As you slowly peel off the backing paper, it will transfer all of the adhesive to the puzzle and it should look something like this:
Step 11: Apply the foam boards
Apply the foam board to the panel from which you just removed the backing paper. I like to start at the corner and then line up the edges. If you lay it down gently, you should be able to carefully pull it back up if it's not aligned properly the first time. Here you can use the rolling pin to apply pressure to the back of the foam board, but not so much that it crushes or dents it. Move to step 12 for that panel.
Step 12: Remove adhesive from uncovered toothed area
After completing the first panel, it occurred to me that when separating the quadrants, that some of the adhesive may stretch and get stuck to the front of the puzzle because I chose to cover the toothed area of the gap with adhesive. I took a Qtip and removed the adhesive from these spots and it came off very quickly and easily by just twisting the Qtip. I would recommend doing this right away in case the uncovered adhesive dries or hardens quickly.
When complete, the back of each panel will be covered with a piece of foam board.
Step 14: Separate the panels
The adhesive may not yet be fully permanent until pressure is applied to the front of the puzzle, so carefully separate each section in preparation for flipping the puzzle.
Step 15: Flip the puzzle
Carefully flip each panel, being careful to not press the pieces along the gap. I prefer to reassemble the puzzle before moving to the next step.
Step 16: Apply pressure to the front of the puzzle
Protect the section that you're working on with the protective sheet included with the adhesive. You can use the rolling pin first, and then the squeegee.
For this puzzle I am mounting it to the wall with Command strips instead of using a frame, which is why I wrapped the edges. If you're following the Command strip method, separate the sections, flip the puzzle, and apply them according to the directions. I recommend making sure to place several along the seams between sections so that they sit flush with each other against the wall. The number of Command strips I used isn't necessary to support the weight, but helps to ensure that the puzzle sits flat on the wall.
Hang one panel at a time.