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This will prevent spray adhesive from getting on your work surface. Completely cover your work surface with newspaper and lay the cut MDF atop it, roughly in the center. Your poster should fit the MDF perfectly. In the event it doesn’t, you may be able to trim the poster with scissors or a utility knife so it fits the backing. If the cut of the MDF is way off, you may need to cut a new mounting for the poster. Take a few clean pieces of paper towel and layer them at about the middle of one half of the poster. Place a clean paperweight on the paper towel. Next you’ll need to cover this half of the poster with more newspaper. Be thorough when covering the weighted portion of the poster with newspaper. Gaps may get sprayed with adhesive and ruin the quality of the finished product. The paperweight should hold the weighted half in place as you do this. The pulled back half should overhang the newspaper covered weighted half. You’re going to be spraying adhesive directly onto the back of the poster, and only the back of the poster. So the MDF exposed by folding back the unweighted half of the poster will also need to be covered with newspaper. Hold the can 6 in (15.2 cm) away from the poster. Position the can of adhesive spray at about the poster’s middle. While you spray, twist your wrist back and forth so the spray passes in an S-shape to coat that half of the poster back. Spray adhesive usually has a strong, unpleasant odor. Allow some time for these fumes to dissipate before moving on. Spraying the back of your poster likely got adhesive on the newspaper covering the weighted portion of the poster and the MDF. Without getting any adhesive on your hands, remove and throw away the newspaper.  Avoid touching the newspaper covering your work surface or moving the MDF after spraying adhesive. This can cause glue to spread to the MDF, which can be a pain to remove. Glue on the side or back of the MDF won't be obvious and, in many cases, can be left to dry. If you’re dead set on removing the glue, rub it lightly with clean paper towel until it comes off. Use a clean piece of paper towel to press the poster onto the MDF starting from the middle and working your way to the edges. Take your time and work in small increments to prevent the formation of bubbles. Bubbles can oftentimes be chased to the edges of your poster where they’ll disappear. Use a plastic card or your clean fingers to gently smooth out uneven parts of the poster. When the glued half of the poster is in place, feel its surface with your clean hands. You’re looking for mis-sprayed glue that got on the poster’s topside or seeped out along the edges. Rub glue gently with clean paper towel to remove it. Glue can discolor the surface of your poster or create roughness. It’ll be easiest to remove errant glue while it’s still fresh. Remove the paperweight and set it off to the side. Cover the glued half of the poster with fresh newspaper and peel back the second half of the poster so it overhangs the covered glued half. Only spray adhesive on the exposed back of the poster.  Before you spray the adhesive, all areas of the poster and MDF should be covered with newspaper except the part that’s been peeled back to overhang the glued half. Smooth the adhesive sprayed poster back to the MDF in the same way you did previously, by rubbing it in small increments with a clean piece of paper towel. The second half of your poster will likely have more glue seep along the edges than the first.

Summary:
Arrange newspaper under the MDF. Orient your poster face up on the MDF backing. Weigh down and cover one half of the poster. Fold back the unweighted side to expose the back of the poster. Cover all remaining MDF with newspaper. Apply adhesive to the poster. Remove all newspaper cover except the work surface cover. Smooth the glued half of the poster onto the MDF. Check for glue and remove seepage with paper towel. Repeat this process on the unglued half of the poster.