Bostik Ultraset® SF Polyurethane Flooring Adhesive

For direct-stick timber flooring installations where boards must remain flat and bonded to concrete slabs without the risk of adhesive re-emulsification from moisture, Bostik Ultraset SF is a solvent-free polyurethane adhesive. It meets the requirements of EN 14293:2006 for bonding parquet to subfloors and is formulated to retain its flexibility after a full cure, accommodating the natural movement of timber flooring systems.

What it does

Bostik Ultraset SF provides a continuous elastomeric bond between timber flooring and concrete subfloors or acoustic underlays. Because it is a 100% polyurethane formulation with zero VOCs and no solvents, it does not shrink during curing and will not damage prefinished timber coatings. The adhesive has been tested to ASTM C794 for peel adhesion to Australian hardwood species, ensuring high bond strength across solid strip softwood, hardwood, engineered timber, and bamboo flooring. It is also suitable for use over radiant heating systems and behaves as a dampening layer to improve acoustic properties.

Numbers that matter

• 600% elongation: High flexibility to absorb the expansion and contraction of timber boards without shearing the bond from the subfloor.
• 1.4 N/mm² shear strength: Tested timber-to-timber under BS EN 14293 to ensure a high-strength, structural bond.
• 1.5 to 2.5 mm per 24 hours cure rate: Cures via atmospheric moisture, achieving a light-traffic walk-on time in 8 to 10 hours and a tack-free state in approximately 4 hours at 23°C and 50% relative humidity.
• 80% minimum bond area: The mandatory contact coverage required between the subfloor and the timber to prevent hollow spots and installation failure.
• 1.1 to 1.3 m² per litre coverage: Average application rate when using standard trowels, varying based on the substrate profile and the selected notch size.

Where to use it

Bostik Ultraset SF is suitable for adhering:

• Parquet, solid strip softwood and hardwood, engineered timber, and bamboo flooring.
• Acoustic underlays to concrete subfloors.
• Direct stick flooring over concrete slabs, joists, battens, plywood, timber, and particleboard.

Limitations

• Do not apply over any acrylic primer or sealer.
• Do not apply to dense, burnished concrete surfaces without first abrading or sanding the concrete to establish a mechanical key.
• Do not apply directly to Bostik PrimeGrip; the adhesive will not bond to it. If PrimeGrip is used, it must be covered entirely with Bostik UL-200.
• Do not use in totally confined or air-free spaces, as the product requires atmospheric moisture to cure. Cure times will extend in low humidity (below 40%).
• Do not use as a waterproofing membrane. It is not designed to waterproof a subfloor.
• Do not install over wet, contaminated, or friable surfaces.
• Do not expose the uncured adhesive to water or alcohol-based cleaners.
• Do not sand the timber floor until the adhesive has cured for a minimum of 24 hours.
• For bamboo flooring installations, two coats of Bostik Ultraseal Vapour Barrier are recommended due to the high moisture sensitivity of bamboo.

Installation and subfloor preparation

Concrete subfloors must be flat to within 3mm over 3m. Any areas exceeding this tolerance must be levelled using Bostik UL-200 over Bostik PrimeGrip. Concrete slabs should be constructed in accordance with AS2870. For ground floor slabs and new concrete less than four months old, apply Bostik Ultraseal Vapour Barrier to a wet film thickness exceeding 300µm to prevent moisture migration. Concrete subfloors are dry enough for timber installation when the Water Vapour Transmission Rate (WVTR) is under 15g/m²/24 hours via the calcium chloride method.

Apply Bostik Ultraset SF using a single application with an appropriate trowel:

• 3mm x 4mm V Notch (1.2 - 1.4 m²/L): Solid and engineered timber <13mm thick, and parquet <19mm.
• 4mm x 5mm V Notch (1.0 - 1.2 m²/L): Engineered timber >13mm thick, and engineered bamboo <13mm.
• 5mm x 8mm x 6mm Flat V Notch (Up to 1.2 m²/L): Engineered timber <13mm and acoustic underlayments.
• 3mm x 3mm x 3mm Square Notch (Up to 2.0 m²/L): Finger block parquet.
• 6mm x 6mm x 3mm Square V Notch (Up to 1.0 m²/L): Engineered timber >13mm, solid wood or bamboo <13mm, and parquet <19mm.
• 6mm x 6mm x 6mm Square Notch (Up to 0.9 m²/L): Solid wood or solid bamboo <13mm, or plywood.

To clean up wet adhesive, use mineral spirits, Shellite, paint thinners, or Bostik Handy Wipes immediately, taking care not to damage prefinished timber coatings.