# Activators and primers Surface preparation that decides whether the bead holds: K-901 activator, K-801 primer. Activators and primers for surface preparation. [K-901 ### Activator Surface activator for glass, metal, ceramic and painted substrates.](https://karmindadhesive.com/products/k-901-activator/)[K-801 ### Primer Black primer that builds the adhesion film under PU and STP sealants.](https://karmindadhesive.com/products/k-801-primer/) ## Compare the models | Model | Tensile strength | Elongation at break | Skin time | Shore A | | K-901 | — | — | 8 | — | | K-801 | — | — | 8 | — | Typical values from the catalogue; the batch record carries the measured result. ## Choosing one Buy the preparation with the adhesive, not after it. K-901 cleans and prepares the frit; K-801 builds an adhesion film where a primerless grade cannot bond. Both ship in 5 ml to 1 L cans with a six-month unopened shelf life, so order against a production date rather than holding stock. ## Where it goes wrong Most "primerless" failures are contamination, not a missing primer. Silicone residue from a previous bead, mould release on a trim, or handling oil on a frit will defeat any activator. The primer is the fallback, not the first answer. Five millilitres is a sample and one litre is a production pack. The shelf-life clock starts at filling, not at opening, so a can without a production date is a can you cannot plan a line around. ## Decision table | If | Then | Because | | New frit, cleaned and dry | K-901 only | the activator removes handling oil | | Unknown substrate or a previous silicone repair | K-901 plus K-801 | the primer builds the adhesion film | | Bare plastic trim | K-801 after a coupon test | some plastics need a specific primer | | Stock has no production date | reorder | six months unopened shelf life, not indefinite | ## Read before you specify - [what primerless really means](https://karmindadhesive.com/resources/primerless-stp-claims/) - [the cure arithmetic](https://karmindadhesive.com/resources/why-windscreen-adhesive-cures-too-slowly/) - [when the topcoat needs a primer](https://karmindadhesive.com/resources/painting-over-seam-sealer/) Send the substrate and the adhesive model and we will confirm whether a primer is required. [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%. - [Industrial and STP](https://karmindadhesive.com/products/industrial/) — Silyl-terminated polymer sealant for metal, plastic and glass — primerless and paintable. - [Wood and glulam](https://karmindadhesive.com/products/wood/) — One-component PUR for engineered timber, glulam beams and sandwich panels.