Polyurethane mastic sealant

KRAFT JOINT PU 25 is one component high-quality polyurethane sealant in the form of thixotropic paste for interior and exterior use. It cures with the humidity to form a tough elastic sealant with excellent resistance to weather conditions. It is recommended for the sealing and bonding between similar and dissimilar substrates in traditional masonry, civil and industry-trial applications, light and heavy prefabrications, interior decorating. Adheres to most construction materials like concrete, glass, tiles, anodized aluminum, and wood. It presents superior elastic performance and movement capability. It is paintable with water-based emulsion paints.

» High mechanical strength
» Elastic performance and movement capability
Very good resistance to aging (UV and moisture)




0.310 L, 0.600 L

  • Instructions


» The substrate must be free of dust and loose particles. Cleaning by means of a wire-brush and blowing with compressed air, if available, is recommended.
» Surfaces should be degreased with solvent, KRAFT WHITE SPIRIT is recommended, using a clean cloth.
» On very porous substrates prime with KRAFT DUR.
» To avoid the soiling of the joint edges put self-sticking paper tape (masking tape) along the edges. This tape must be removed immediately after sealing (before curing of the sealant).
» Cut tip off cartridge and screw the nozzle onto the cartridge. Cut the tip of nozzle at an angle to achieve the desired bead size. Apply sealant with a caulking gun in a continuous bead to the prepared joint. Smooth down after application before skin formation occurs, by using a flat or rounded tool.
» For good performance it is essential that the sealant be only bonded to the two facing sides of the joint. To achieve this install a backup material (closed cell polyethylene or open cell polyurethane foam). Apply the sealant in a continuous operation making sure all air pockets or voids are eliminated. Tool the sealant with light pressure to spread the material against the joint surfaces. This operation should be made with a dry spatula before skin formation occurs.
» Cleaning: Excess uncured sealant should be wiped and cleaned with a KRAFT WHITE SPIRIT. Cured sealant can only be removed by abrasion.

» Do not apply at temperatures below 5ºC and above 35ºC.
» Joint width should be twice the depth when the width is bigger than 20mm and equal to the depth when the width is smaller than 20mm. The width of the joints should not be less than 5mm or bigger than 50mm.
» Not suitable for continuous exposure to water.


» Store containers in dry conditions at temperatures between 5ºC and 35ºC. Shelf life of at least 18 months in the original unopened containers.


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