Use X-acto knife to pry layers apart if possible, then repair as completely delaminated below.
If the plies wont come apart, then use X-acto knife to insert glue into the crack and dry under pressure in vise as below.
Completely Delaminated pieces:
Scrape off old glue with razor blade
Always work on bottom ply up to paper top to avoid handling the paper layer any more than necessary. The thickest layer is almost always the middle ply.
Apply Elmers Wood Glue to small paint brush and coat sides of both pieces of wood which are to go together.
Hold layers together square against table on various sides. Continue with next layer(s).
Use Elmers Glue-All to attach paper layer to top ply.
Carefully insert reglued pieces (partially and wholly) between release paper, which is between 2 pieces of wood; then place into vise and tighten. While handling reglued piece, constantly check to see if ply layers have shifted; if so immediately pull apart, reglue and insert into vise.
Leave overnight; remove next day and use Dremel drill to grind off any excess glue and any ply below the picture level extending beyond the picture resulting from slippage or expansion. In other words, looking straight down at the piece, no ply must extend beyond the top layer of ply and picture.
Ply layer missing substantially or entirely.
Use 1/16 plywood (or thinner if available) and glue onto puzzle piece following steps above.
Next day, adjust your scroll saw table so that blade slants toward center of piece. Carefully cut off excess ply. Check for fit. Be sure to readjust your scroll saw table so that blade is returned to perpendicular.
Sand back of relaminated piece down to puzzle level.
Glue broken pieces together with Elmers Wood glue.
To insure original shape, insert reglued piece into puzzle using bits of release paper on each side of repair area.
If a small piece of ply at top or bottom of break is missing, use Elmer Wood glue and Plastic Wood in missing area and grind off excess with Dremel tool after it dries. 3. Touch up break with watercolor pencils.