People use poster board or "paper board"--a type of cardboard usually sold in thin sheets or as two thin cardboard sheets layered with a foam centre--in a wide array of projects. As a single sheet of poster board can bend easily, people often need to "stiffen" the poster board to make it sturdier. Whether you need sturdier poster board for posters, signs, ornaments, costumes or even faux jewellery, you can easily stiffen it for any project with a few art and home supplies.
Layer poster board and/or printer paper pieces to make a stiffer, single poster board. On a hard, flat work surface, cut identical pieces of poster board with your scissors or a paper cutter. Brush a thin layer of white school glue or white-to-clear puzzle glue across one piece. Align a dry piece of poster board or printer paper over the top of the wet poster board, and stick together. Rub the edge of your plastic putty knife across the piece to flatten and create the first "air-bubble free" layer of your stiffer poster board.
Repeat with additional layers. Air-dry your layered board after applying three to four layers as the wet glue can cause the board to curl or feel damp. When the board no longer feels damp to the touch, glue on additional pieces of poster board or paper as desired.
If any edge of your layered poster board doesn't have enough glue, apply a thin bead of glue to the edge. Run your putty knife gently along it to press together the layers and then wipe away any excess glue with a lint-free, white microfiber cloth.
Glue thin fabric or canvas to the back of your poster board to stiffen it. Brush a thin layer of glue on the board. Place your fabric/canvas on the centre of the glued surface, and then flatten the fabric outward across the board to each corner and the sides using your putty knife or the palm of your hand.
Allow the surface to air-dry, and then apply additional coats of glue to the fabric and poster board back as necessary until the board has stiffened to the level required for your project.
If you want to create poster board with a stiff centre, start with the thickest piece of poster board that you have. Brush glue on the piece, and then add layers to both side of the board--gradually decreasing the thickness of the poster board or paper pieces as you add the final layers. If you're project requires the use of an extremely stiff piece of poster board and/or cutting of an intricate design from the stiff board, create and cut out your design on a thin piece of poster board first. After decorating the design, glue on a thicker and wider board or fabric to the back--to give it support/stiffen it---and then cut away any remaining excess board or fabric. If you need to stiffen "foam core" poster board, mix one part water to two parts white school glue and pour the solution down through the foam centre of the board to harden the foam.
Use only white microfiber cloths as coloured cloth can leave a dye stain behind on wet glue surfaces.