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You don't need a degree in chemical engineering to understand how to apply caulking and sealants for air tight assemblies, but you do need to know about the product you're using.

Common products:

• Acoustic sealant - Synthetic rubber polymer; doesn't harden; good for VB overlaps - may be messy and hard to clean up without solvents.
• Silicone caulking - Silicon, oxygen polymer; cures to a rubbery, flexible state; Interior and exterior application; good around heat; fill cracks up to 1/4".
• Low expansion spray foam - open cell polyurethane foam that expands to fill cracks (larger than 1/2" - 1.25 cm); stays a bit soft after curing; can expand out of the joint and require some clean up (cutting / scraping).
• Elastomeric Spray / Roll On - Liquid applied air barrier and sealant is flexible and durable once cured.

CONSIDERATIONS:

• Temperature - If the ambient temperature in the building is below freezing, any caulking or foam sealant is going to have trouble adhering. Early spring or late Fall and winter - you need to have the space warm enough for proper application.
• Location? - Caulking is good for small cracks and gaps, or for sealing behind VB or panels. Larger gaps should be filled with appropriate insulation or foam backer rods.
• Material differences - If you've got a piece of glass that needs sealing to a wood or metal surface, it's better to use a rubber butyl product than caulking. Any moving parts, like doors and windows, will need weather strip material.

SPECIAL NOTE: Always clean the area you are about to caulk or seal. Sawdust and dirt can mess up the application and lead to unplanned gaps.