Caulking compounds are specifically formulated flexible sealants designed to fill and seal joints or gaps against air, water, or sound infiltration. Other mastics under 3214100020 encompass adhesive or gap-filling preparations that do not function primarily as joint sealants. The product's intended end-use and formulation characteristics — particularly flexibility and substrate adhesion profile — guide the line between these two tariff lines.

No broad Section 301 or antidumping orders are widely known to target mastics as a category, but importers should verify current CBP and Commerce Department orders at the time of entry, as trade-remedy coverage can change. Canada and Mexico, the leading suppliers, benefit from USMCA treatment when origin requirements are met.