Couch arm repair for styrofoam couch frame
Couch arm was broken because it's made of styrofoam and we probably leaned on it too hard. It's padded with a regular yellow foam sheet. I couldn't find any how-to on fixing this so I want to share. Hope it helps someone!
Remove staples along the bottom and undo a seam of the fabric enough to access the full side. Push the arm in place to be level. Glue any styrofoam that makes contact along line of crack with wood glue. Wood glue is important - many types of glue will melt it! Use rope or something to make sure it stays level and in place while drying. Let dry for a day and maybe do two layers.
Get "Great Stuff Gaps and Cracks Insulating Spray Foam Sealant" (I needed 2). Fill all empty areas between the styrofoam with this, layering as you go. Let dry, and use a knife to shave the side of the couch to be flat and flush with the original styrofoam. I filled in any uneven parts after this and repeated the shaving. I used sandpaper to finish it off.
Use a staple gun and staple the yellow foam sheet on top of the styrofoam layer. My couch had thin wood on the top (under the arm) and underneath the bottom edge of the couch - staple into the wood.
Using the other arm as a reference, I flipped the couch upside down and stapled the fabric back onto the bottom of the couch. I had to sew one seam towards the back that I had undone to access the foam side. Make it as neat as possible, and done!