What about polyester resin, perhaps to attach fiberglass, or as fill coat under epoxy paint or other paint. I used this method at one time. Very hard and strong. Years back (30 plus years as a matter of fact) we purchased an inexpensive sofa, made of press board and ply. Slats supporting the seat cushions were held in place by planks glued to the press board. Good for about a year. Then crash. I tried different glues, including epoxy to re-glue. Crash and crash again. At that time I used polyester resin as a fill coat on profiles, color painted with Hobby Poxy. One coat resin, scraped off as much as possible, one coat Hobby Poxy. I mixed the resin in paper cups. The left over resin setup up in the bottom of the cup. Tough stuff. Out of curiosity I took a hammer to the left over resin. Couldn't make a dent. I slugged it hard as I could. As a last resort to fix the sofa I mixed up the resin to glue the supporting planks. It worked. Laying on that piece of junk to this day. (Looks pretty good, the veneer has not stripped, an oriental rug on top-- improvised posh.) Anyone use polyester resin these days?