Two types of adhesives?

• A. Contact and No Contact
• B. Water-Based and Solvent-Based
• C. Pressure-Sensitive and Hot-Melt
• D. Mechanical and Chemical

Answer: (A)

The main idea is how the bond forms between surfaces. Adhesives are usually grouped by whether they create the bond at the moment of contact or whether they need curing after application.

With contact adhesives, the surfaces touch while the adhesive is tacky and a bond is formed immediately under pressure. This means you have to position parts very carefully before bringing them together, because once contact is made the bond develops right away and isn’t easily repositionable.

Non-contact (no-contact) adhesives rely on curing or drying after application. You apply the adhesive, place the parts, and wait for it to set through solvent evaporation or a chemical reaction. This allows you to adjust the fit a bit during setup and results in a bond that gains strength as it cures.

The other pairings describe properties or mechanisms (like being water- or solvent-based, or the type of bond like mechanical vs chemical), but they don’t capture the fundamental bonding behavior the question targets.