Construction joints
Concrete, tunnel and drainage sealants — 550–615% elongation, elastic recovery up to 80%.
KA340A
Construction Sealant
Flexible sealant for concrete joints, tunnels and drainage.
KA340B
Construction Sealant
Low-movement, water-pressure-resistant grade for tunnels and drainage.
Compare the models
Typical values from the catalogue; the batch record carries the measured result.
Choosing one
Pick by movement first. A façade joint that opens 25% needs the softer KA340A at 615% elongation and 75% recovery; a below-grade or drainage joint that resists water pressure needs KA340B and its higher modulus. Movement class decides, then substrate condition, then primer.
Where it goes wrong
A joint that leaks at the flank was usually sealed green, primed on a damp face, or detailed deeper than it is wide. In a 20 mm joint the last one is easy to do: 25 mm of sealant over no backer rod cannot stretch, so it tears instead of following the movement.
Elongation and recovery are different claims. 615% tells you how far the bead stretches before it tears; 75% tells you how much it comes back. A joint that stays open needs the first, a joint that cycles needs the second.
Decision table
| If | Then | Because |
|---|---|---|
| Facade joint with ±25% movement | KA340A | 615% elongation and 75% recovery |
| Tunnel or drainage joint under head | KA340B | higher modulus and 80% recovery |
| Concrete is less than 28 days old | wait | mix water still leaving the slab lifts the bead |
| The joint is deeper than it is wide | backer rod first | three-sided adhesion cannot stretch |
Read before you specify
Other families
- Automotive glass bonding — Windscreen, side and rear glass adhesives — 310 ml cartridges, sausages and 200 L barrels.
- Body and sheet metal — Seam sealers for body panels, doors and container joints — sandable, paintable, four colours.
- Industrial and STP — Silyl-terminated polymer sealant for metal, plastic and glass — primerless and paintable.
- Wood and glulam — One-component PUR for engineered timber, glulam beams and sandwich panels.
- Activators and primers — Surface preparation that decides whether the bead holds: K-901 activator, K-801 primer.