# Industrial and STP Silyl-terminated polymer sealant for metal, plastic and glass — primerless and paintable. PU and STP sealant applications. [KAM921 ### STP Sealant Silyl-terminated polymer sealant: silicone weathering, PU strength, paintable.](https://karmindadhesive.com/products/kam921-stp-sealant/) ## Choosing one Choose STP for exterior panel joints and mixed substrates, not for structural load. KAM921 is UV-stable, paintable and primerless on most metals at 1.8 MPa and Shore A 40, which is roughly half the tensile of a glazing PU. If the joint carries load, this is the wrong family. ## Where it goes wrong STP fails on load, not on weather. A panel joint that looks fine for two years can creep if it was sized for movement but loaded in shear; the same bead on a structural bracket will not hold 1.8 MPa for long. Keep STP on movement, and use a structural adhesive where the drawing says so. Shore A 40 is the handling number. It is soft enough to tool with a spatula and firm enough not to sag on a vertical panel, and the 450% elongation is what lets it follow thermal movement without peeling at the edge. ## Decision table | If | Then | Because | | Mixed metal, plastic or glass, outdoors | KAM921 | primerless on most substrates and UV stable | | The joint carries structural load | a structural adhesive | 1.8 MPa is a sealing figure, not a bond strength | | The bead will be overpainted | KAM921 | paintable once fully cured; test the topcoat | | Permanent immersion | not STP | hydrolysis risk in continuously wet joints | ## Read before you specify - [what STP is and is not](https://karmindadhesive.com/resources/stp-sealant-guide/) - [where each family belongs](https://karmindadhesive.com/resources/pu-sealant-vs-silicone-sealant/) - [paint adhesion over a fresh bead](https://karmindadhesive.com/resources/overcoating-stp-sealant/) Send the substrate, joint width and UV exposure and we will confirm whether STP or PU is the right family. [martin@karmindadhesive.com](mailto:martin@karmindadhesive.com) ## Other families - [Automotive glass bonding](https://karmindadhesive.com/products/automotive-glass/) — Windscreen, side and rear glass adhesives — 310 ml cartridges, sausages and 200 L barrels. - [Body and sheet metal](https://karmindadhesive.com/products/automotive-body/) — Seam sealers for body panels, doors and container joints — sandable, paintable, four colours. - [Construction joints](https://karmindadhesive.com/products/construction/) — Concrete, tunnel and drainage sealants — 550–615% elongation, elastic recovery up to 80%. - [Wood and glulam](https://karmindadhesive.com/products/wood/) — One-component PUR for engineered timber, glulam beams and sandwich panels. - [Activators and primers](https://karmindadhesive.com/products/accessories/) — Surface preparation that decides whether the bead holds: K-901 activator, K-801 primer.