As a warning I'd recommend to stay away from most commercial puzzle glues. Some of them are water based - and this doesn't go well with cardboard. Anything bigger than 1000 pieces will start to warp a lot.
What people may not realize also is that at this "scale", it can happen that a piece perfectly fits in more than one location. And I don't mean a couple of cm apart, complete opposite sides of the puzzle. Fun times figuring this out.
This is the one https://m.media-amazon.com/images/I/81C6LLOhsgL._AC_SL1500_....
1 - https://en.clementoni.com/collections/adult-puzzle/products/...
Apparently Mod Podge is a brand of craft products and adhesives: https://mod-podge.com/
Having a soft base helps when transporting. I once had to move a 9.000 piece puzzle - and without some bending it would have been difficult getting it into the car.
For the biggest jigsaws out there it gets difficult to find a good wall for it. Weight and bending of wood or MDF can become an issue. And even some walls are not as flat as they look like...
Further considerations:
Multi-ply is frequently available in 5'x5' sheets and can be tough to find in 4'x8's. MDF is universally 49"x97" (so you can net a 4'x8' after accounting for the dinged up edges). The size of your puzzle may inform your choice.
Home Depot et al. will usually cut a sheet to size on their panel saw. Your local lumberyard may or may not be interested in doing so for a small order.
Home Depot et al. generally aren't interested in delivering for an even half reasonable price if they do it at all. A real lumberyard might be willing to do so, though it's unlikely to be cheap for a single sheet order ($25 for an order under $500, last I needed a delivery. Cheaper than owning a truck or van for me). They also usually dispatch trucks on a schedule. Mine goes north on Tuesdays and south on Thursdays, for example. Plan ahead and don't expect your stuff to show up like Amazon packages the next day.
For the 9.000s I always used paper for the backside (old calendars are a good source for big sheets with excellent quality). Using one wooden lath at the top was enough to ensure stability for a 18.000. The 9.000s didn't need that - just paper and a bit of duct-tape on the backside were enough.
I found that a coating of quick-drying, low-viscosity liquid glue on the front side works pretty well, because the glue easily flows into the gaps between the pieces, and then into the space between the puzzle and the board. Once the glue dries off, all the pieces and the backing board become a single chunk of cellulose-infused plastic. This is probably much better than either the thick mod podge or the adhesive sheet that OP tried to use at first.
Or sheet of hardboard and a stanley knife, which is probably the most sensible option in context.
All in all when I needed a one-off cut I used a box cutter knife, and when I needed a series I used a circular saw with a plywood blade. The setup is similar (needs an offset guide) but the cut is much straighter, faster, and less error prone. I think the only time I'd use a jigsaw is for making non-straight cuts like some curved artistic shape or something.
(Like mentioned I did have it in the reply as well)
Proper track saws though tend to come with finer tooth blades with a thinner kerf so that they cut cleaner than a circular saw. They also retract within a kind of housing so that they're safer — only plunging down when you lean on them to make the cut.
Once you use one, you'll not go back to your circular saw unless, for example, you're trying to cut some framing lumber in place.
I have a Makita [1] which I like a lot, but my sister, wanting to save a little dosh, got a Kreg [2] and is happy with it.
[1] https://www.amazon.com/Makita-SP6000J1-Plunge-Circular-Stack...
[2] https://www.amazon.com/Kreg-ACS-SAWBB-Plunge-Cut-replaces-AC...
I had a 12,000 piece puzzle mounted and framed by a framing store. I forgot the details, but they used something called "Gator Board" (they could get it 10-foot sheets, along with a 10-foot long piece of plexiglass) and they used a machine the heat up the adhesive in sections. They used two separate sections of Z-channel which is apparently what museums use to hang frames. And they advised that I use washers to line up the Z-channel since most walls are not straight.
My original plan was to glue it to a single 10x6 piece of plywood that I could get custom ordered for $300, but even though the mounting and framing cost me $2300, it was well worth it (I got a really nice gilded frame).
(In fact I didn't get laid off — wrote about it here: https://engineersneedart.com/blog/puzzle/puzzle.html)
Another topic would be how to safely attach a puzzle onto a ceiling... This would add more options.. Putting it on the floor could also work, but adds entirely new requirements for protection... Maybe that path would end up in building a glass floor...
We always glue and frame our puzzles when we are finished (using standard off-the-shelf framing kits from Amazon - nothing like the scale of this article) and display them proudly in a common area of the house for a while after we finish.
But I can see why it's not for everybody, which is totally fine. More open-ended projects are also great.
I know that they had to save the company with licensing etc, but it seems way more about building a particular thing, then never breaking it apart now.
For me I think the change came when I was able to build more real things. I learned how to solder, and then I learned woodworking, and all of a sudden I could make something that's the exact shape I wanted. Once you have those abilities it's a lot harder to go back.
Of course the really cost-effective way to get it remains buying it second-hand by the kilogram.
Adults getting in on the game and dropping hundreds on nostalgia-provoking kits is a relatively newer thing, but it's not preventing access to freeform building supplies.
Nicely done, though :-)
What blew me away with this 9000 piece is the freakin size of it. I had this impression it was maybe 1 meter along its longest edge until the last picture of the author standing in front of it. That is huge and the assembly must require a dedicated space. Then I see people here talking of 13200 and 24000 piece puzzles... Madness!
Kinda want to put together a puzzle now...
The solving part is fun but the later handling can use some work to be optimized.
