Which technique helps reveal delaminations in plywood panels?

• A. Testing with a hammer to break the panel.
• B. Pouring water on the surface.
• C. Tapping the panel to hear hollow sounds.
• D. Painting the panel with varnish.

Answer: (C)

Delamination shows up in the way a plywood panel vibrates when you tap it. Plywood is made of glued layers, so when the glue bond fails and layers separate, that area becomes loose. Striking the panel with a small hammer or tapping tool sends a sound wave through the wood, and how that sound comes back changes with the condition of the bond. In solid, well-bonded areas, tapping sounds crisp and resonant; in delaminated spots, the sound tends to be hollow or dull because the layers can move a bit independently and don’t transmit sound as well. By listening carefully as you tap across the surface, you can spot areas that don’t sound right and indicate delamination without cutting or damaging the panel further.

Hammering hard to break the panel would damage it, pouring water on the surface doesn’t reveal internal separation, and painting with varnish won’t show whether the layers have separated inside.