It sometimes is possible to salvage water-damaged wood veneer, but not always. When the veneer is laid over particle board, fiberboard or thin plywood, that material also might be wet and usually swells. In this case, repair might not be possible. Veneer laid over hardwood might be easier and more worthwhile to fix. Water that settles on top of the veneer can cause it to blister. Water that collects at the edges can cause the veneer to ripple. The veneer comes loose because the glue holding it on is diluted by the water.
Split any blisters with the utility knife. Cut with the grain of the veneer, not across it. Avoid cutting into the wood beneath the veneer. Slice blisters two or three times if they are more than 1 or 2 inches in diameter. Put the glue into the syringe. Insert under each section of the split veneer, and apply glue. Repeat this until all of the blistered sections are reglued. Place a sheet of waxed paper over each blistered area. Place heavy books on top. Leave for two days or until veneer is flattened and adheres well to underlay.
Split ripples at the edges of the furniture if they are long, and glue them as you did the blisters. Glue shorter ripples without splitting them. Lay waxed paper over the rippled area, and place the board over the waxed paper. Clamp all together with the C-clamps. Leave overnight. Remove clamping set-up when the veneer is flat and adheres to the underlay.
Patch the veneer where it cannot be reglued and flattened. Lay cardboard over the area you want to patch. Tape it down. Lay a straight edge on the cardboard, and use it to size a piece of cardboard slightly larger than the size of the damaged area. Cut through the cardboard and damaged veneer beneath with the utility knife. Cut with the grain; do not cut right angles. A diamond shape or trapezoid shape works best; these shapes prevent corners on the patch that might come unglued later.
Remove the cardboard and the damaged veneer. If old glue sticks to the underlay, sand it off with a fine-grade sandpaper. Use the cardboard as a template to cut the patch from the new veneer sheet. Use the straight edge, cutting with the grain. Smear glue on the veneer patch, making sure to cover it completely, and set it carefully into place. Lay waxed paper over the patch, and weight it with the books if it is on the surface of the furniture or with the clamp method if it is near an edge. Leave overnight.