Bostik's BEST® 4 Gallon is a high-performance, moisture-cure urethane wood-flooring adhesive and moisture-control membrane designed for demanding residential and commercial hardwood installations. Its high-tack formula provides strong green grab immediately after troweling while remaining flexible enough to move with wood flooring as temperature and humidity change.

Bostik's BEST can be used with engineered hardwood, solid hardwood, bamboo, cork and parquet over properly prepared substrates including concrete, plywood, OSB, well-bonded vinyl/VCT, ceramic tile, cement backer board, cementitious patch and underlayment, dry above-grade gypsum underlayment, terrazzo and radiant-heat flooring. The adhesive contains no water, is low VOC, and includes Bostik's BLOCKADE® antimicrobial protection on the surface of the cured adhesive.

When applied as directed as a moisture-control membrane beneath dimensionally stable engineered hardwood, Bostik's BEST reduces moisture-vapor transmission through properly prepared concrete. It also functions as an anti-fracture membrane and can bridge substrate cracks up to 1/8" (3 mm).

Contractor Notes

• Install with the appropriate Bostik trowel and verify full adhesive transfer as work progresses.
• Concrete must be properly prepared, porous and free of contaminants; Bostik specifies a CSP 1–3 surface profile.
• Maximum acceptable floor variation is 3/16" in 10 ft.
• For engineered hardwood moisture-control applications, the slab must be fully cured, properly prepared and dry to the touch.
• For solid hardwood or bamboo over concrete above 3 lb MVER or 75% RH, use the moisture-mitigation system specified by Bostik rather than relying on BEST alone as the moisture membrane.
• Do not use where hydrostatic pressure is present.
• Slab temperature during installation should be approximately 50°F–95°F; product application temperature is listed at 50°F–100°F.
• Light foot traffic is typically allowed after approximately 6–8 hours; normal traffic follows after cure in accordance with the current TDS and jobsite conditions.

Frequently Asked Questions

• Is Bostik's BEST both an adhesive and moisture-control product? Yes. It is a urethane wood-flooring adhesive that can also provide moisture-vapor control beneath dimensionally stable engineered hardwood when applied according to Bostik requirements.
• What flooring can it install? Engineered hardwood, solid hardwood, bamboo, cork and parquet, with additional approved specialty applications described in the current TDS.
• Can it bridge cracks? Yes. Bostik states the cured elastomeric membrane can bridge substrate cracks up to 1/8".
• Does it contain water? No. Bostik lists it as a one-part moisture-cure urethane with 0% water.
• Is it low VOC? Yes. The current TDS lists VOC compliance at 20 g/L using EPA Method 24.
• What color is the adhesive? Tan.

Documents & Resources

• Bostik's BEST Product Page
• Technical Data Sheet
• Safety Data Sheet
• Bostik Commercial Hardwood Flooring Installation Products Limited Warranty
• FloorScore Certification
• CSI 3-Part Wood Flooring Installation Products Specification