Which glue comes in various grades defined by the degree of water resistance and is not suitable for humid climates?

The correct answer is that PVA (Polyvinyl Acetate) glue comes in different grades that vary based on their water resistance properties. It's commonly used in woodworking, especially for projects requiring a strong bond between pieces of wood. However, standard PVA glue is not waterproof, making it less suitable for humid climates or situations where the bond may be exposed to significant moisture.

PVA glue is typically categorized into interior and exterior grades, with the exterior variants offering better resistance to moisture. Nonetheless, even the best exterior grades may not withstand constant exposure to water, which is why it is recommended to use them with caution in humid environments.

In contrast, other adhesives like contact glue and polyurethane offer different bonding characteristics. Contact glue achieves strong adhesion on surfaces, making it suitable for laminates and wood veneers, but it does not have the same grading based on water resistance as PVA. Yellow carpenter's glue, while often used for wood projects, falls under the category of PVA but still shares its limitations regarding water resistance. Polyurethane glue is known for being waterproof and highly resistant to moisture, making it a suitable choice for humid conditions.