Plywood has been used for years to build tables, due in part to its split-resistant quality. It finishes like solid wood and is extremely flat, easy to work with and affordable. Plywood used on tables has a thin surface veneer glued under pressure to a layered core of softwood or composite material. Over time, the glue can loosen, releasing the veneer, causing it to lift. The problem might be anywhere along an edge, or in some cases, near the middle, where it causes a bubble.
Popped Up Along an Edge
Insert the tip of a putty knife under the loose edge of the veneer. Use it to scrape out any crystallized glue particles, debris, or anything that might prevent the veneer from laying flat.
Pry the popped up veneer up slightly with the putty knife. Inject glue under the popped up veneer with the tip of a glue bottle. Spread the glue evenly under the loose veneer with the putty knife. Press the veneer down flat with your fingers.
Stretch strips of masking tape across the loose veneer, down over the edge of the tabletop, spaced 1/4 inch apart. Stretch the tape as tight as possible without breaking it. Place a block of wood on the glued area. The block should be bigger than the glued area. Place heavy objects on the block or use clamps if the area is accessible to clamps. Allow the glue to dry overnight.
Remove the heavy objects and the block. Scrape off any residual dried glue with the tip of the putty knife. Color the edge of the veneer with a matching stain-marker to finish.
Popped Up in the Center
Cut a 1 1/2-inch long slit in the top of any large bubbles that you can't access from an edge. Use a craft knife to cut the slits parallel with the grain. Cut additional slits spaced 1 1/2 inch apart if the popped-up area is bigger than 3 inches across. For bubbles smaller than 1 1/2-inches in diameter, cut the slit just big enough to insert the tip of a glue bottle. For tiny bubbles, poke a small hole in the bubble big enough to inject some glue.
Pry the slits apart with the tip of a putty knife. Inject glue into the slits with the tip of a glue bottle. Insert the putty knife into the slits to spread the glue around as much as possible. For the smaller bubbles, inject the glue directly into the hole with the tip of the bottle.
Press the popped up area down with your fingers. Place plastic wrap on the popped up area. Place a block of wood on top of the plastic wrap. The block should be bigger than the popped up area. Place heavy objects on the block. Allow the glue to dry overnight.
Remove the heavy objects, block and plastic wrap. Use a chisel to scrape of any dried glue. Apply putty crayon or stain marker to the slits if you can see them. Polish smooth with a piece of denim.