Polyurethane Joint Sealant - Koster PU Flex 25

Koster PU-Flex 25 is a highly elastic, low modulus polyurethane sealant, with good UV resistance and excellent adhesion to typical construction materials. Koster PU-Flex 25 is one component and cures with moisture to form a flexible sealant which can be overpainted after curing is finished.

Features and benefits:

• The sealant is non sagging.
• Highly thixotropic.
• Easy smoothing and workability.
• Highly elastic joint sealant.
• Multiple substrate application - Easy application on horizontal. and vertical surfaces.
• For interior and exterior use.
• Single component - no mixing required.
• Fast application with only a caulking gun.
• Less waste through tubular bags instead of plastic cartridges.

Designed for civil and industrial movement, expansion, control and dilatation joints in both architectural and heavy construction. This versatile material can be used to seal many types of substrates including:

Porous substrates (no primer required):

• Concrete.
• Mortar.
• Brickwork.
• Blockwork.
• Natural and synthetic stone, etc.

Non-porous substrates (Koster PU Primer 120 required):

• Metal.
• Steel.
• Aluminum.
• Wood.
• Ceramic tiles.
• Rigid plastics, etc.

Preparation and priming:

Ensure that the air and substrate temperatures are +5°C or higher and that all surfaces are clean, dry and free from dust and grease. Clean, porous, absorbent substrates require no primer. Use Koster PU Primer 120 for nonporous (non-absorbing) surfaces.

Insert a closed-cell foam backing rod into the joint. this backing rod should be compressible and tight fitting. Depth for insertion will depend on the joint width (see below for ratio advice).

Application:

Koster PU-Flex 25 is installed with the Koster Special Caulking Gun (without attachments). Joint widths up to 10 mm are filled in the width / height ratio 1:1, from 10 to 30 mm with a ratio of 2:1. For critical substrates or unknown materials it is recommended to carry out adhesive pull-off tests prior to installation. If the substrate has a layer which may not be removed (eg coatings), adhesion and compatibility tests must be carried out in advance.

Hand pump the material into the joint - against the backing rod - until it is flush with the wall surface. Finally smooth the uncured material.

Materials:

• Primer: Koster PU Primer 120.
• Sealant: Koster PU Flex 25.
• Backing rod: Closed cell (by others).

For further information or design assistance, please contact Technical@kosteruk.com and we will be happy to assist.