Surface Preparation
To begin, ensure the substrate is structurally sound, clean, and dry. Remove all contaminants such as dirt, grease, oil, old paint, or sealant residue. For specific materials:
- Concrete or Masonry: Clean the surface using grinding, sandblasting, or wire brushing to remove contaminants.
- Wood: Scrape away loose paint to expose bare wood and test any coatings to ensure proper adhesion.
- Metal: Remove rust, scale, and loose coatings to expose a bright, clean surface.
Joint Design and Depth Control
When designing the joint, follow the guidelines established by the SWR Institute. The sealant depth should be 50% of the joint width, with a minimum depth of ¼ inch and a maximum of ½ inch. For deeper joints, insert a backer rod to control the sealant depth. Compress and roll the backer rod into the joint channel without stretching it, ensuring it fits snugly. If the joint is too shallow for a backer rod, use bond breaker tape to prevent three-point adhesion.
Priming (If Necessary)
Sikaflex NP 1 generally does not require primer; however, special conditions may necessitate its use. For applications involving immersion or green concrete, apply Sikaflex Primer-173. Use a brush or clean cloth to apply the primer in a light, uniform coating. Allow the primer to dry for 15 to 120 minutes, depending on temperature and humidity, before applying the sealant. Always test the adhesion of the primer and sealant on-site to ensure compatibility.
Sealant Application
To apply Sikaflex NP 1, cut the nozzle tip of the cartridge to the desired bead size. Use a caulking gun to dispense the sealant in a continuous motion, filling the joint completely. After application, tool the sealant with a spatula or similar device to smooth the surface, ensure proper contact with the joint edges, and remove air pockets. Tooling should be completed before the sealant begins to form a skin.
Curing and Clean-Up
Allow Sikaflex NP 1 to cure fully before exposing it to water or movement. Curing time will vary based on environmental conditions such as temperature and humidity. Clean tools and any accidental spills immediately using a suitable solvent, as specified in the product datasheet.
Additional Tips for Best Results
For optimal application, use Sikaflex NP 1 within a temperature range of -40°F to 180°F (-40°C to 82°C). Store the product in its original, unopened container away from direct sunlight and elevated temperatures to maintain its shelf life.