Make sure the puzzle is fully assembled and the surface is flat
Slide a piece of cardboard or wax paper under the puzzle
Apply puzzle glue evenly over the front surface
Spread the glue with a brush, sponge, or applicator if needed
Let the front dry completely
Carefully flip the puzzle over if you want to glue the back
Apply glue to the back if desired for extra strength
Let the back dry completely
Place the glued puzzle on a flat surface until fully cured
Mount or frame the puzzle once dry