After you invest hours of work putting together a 5000-piece puzzle, the last thing you want to think about is taking it apart. If you just can't bring yourself undo all that hard work, consider preserving the finished puzzle. You can use Mod Podge brand's Puzzle Saver or another decoupage glue to hold the pieces together.
Slide a piece of cardboard or newspaper under the puzzle to protect your table.
Dip the sponge brush into the glue or squirt the Puzzle Saver glue directly onto the puzzle. If your brush is too wide to fit in the container, pour a little bit of glue in an old dish or plastic bowl.
Spread the glue on the puzzle in a thin layer. Use just enough to coat the entire face of the puzzle.
Allow the first layer to dry completely. Apply a thicker second coat and allow it to dry. You should be able to slide the entire puzzle from side to side and it should feel fairly sturdy.
Flip the puzzle over carefully. Use the piece of cardboard to help you flip it upside down and then slide the cardboard back under the puzzle.
Coat the back of the puzzle with glue and allow this coat to dry. This should make your puzzle sturdy enough to transport and display.
If you want to display your puzzle, you can tack it to a wall by pushing tiny nails or thumbtacks right through the puzzle. Another option is to frame the puzzle.
If the brushstrokes show in the finish, sand it lightly or apply a thicker coat to even out the ridges.
If you are doing this on a table and feel that there may be glue that has soaked through the puzzle, slide it to the side and wipe the glue off the table before it dries. Then slide it back again and check for glue in the new area. Do this until you feel all the glue has been removed. Once it is dry, it cannot be wiped off.