Glue-Down Engineered Wood: Trowel and Adhesive

Glue-down engineered wood depends on one thing above all: full adhesive contact. The adhesive's data sheet sets the trowel, the coverage and the slab limits. The examples below use Bostik's BEST urethane^[1] and SikaBond-T55;^[2] use the numbers for the adhesive you're actually using.

Check the slab

Moisture problems are the most common cause of glue-down failures, so test before anything else.

• Run the moisture tests the adhesive and flooring makers call for. See Subfloor moisture testing.
• Used as a moisture membrane under engineered flooring, Bostik's BEST has no slab moisture limit as long as the slab is dry to the touch. Under solid or bamboo the limit is 3 lb/1,000 sq ft/24 hr or 75% RH; above that, use Bostik MVP4 or a different adhesive system.^[1]
• Remove old cutback residue completely before using urethane. See Removing glue-down hardwood.
• Check flatness. See Subfloor flatness.

Trowel and coverage

The notch depends on whether you're also using the adhesive as a moisture barrier.

• As a moisture membrane, Bostik's BEST needs full coverage of the slab and full transfer to the back of the flooring. As an adhesive only, it needs more than 80% coverage and transfer for engineered wood and more than 95% for solid.^[1]
• Replace worn trowels. A worn notch lays down less adhesive than the spec.

Open time and temperature

Open time varies a lot between adhesives.

• Bostik's BEST has up to 180 minutes of open time depending on temperature and humidity, goes down at 50 to 100°F, and takes light traffic after 6 to 8 hours.^[1]
• SikaBond-T55 has a skin and laying time of 45 to 60 minutes at 73°F and 50% RH, and takes light foot traffic after about 4 hours.^[2]
• Only spread what you can cover within the open time.

Step by step

With the slab checked and the trowel picked, the install follows a steady routine.

1. Snap a starting line and set a straight first row, secured so it can't drift.
2. Spread adhesive with the specified trowel, holding it at a consistent angle.
3. Set boards into wet adhesive and press them down fully.
4. Lift a board now and then right after setting it to check coverage on the slab and transfer to the back.^[1]
5. Tape boards together with removable blue tape to keep them from sliding.^[1]
6. Clean adhesive off prefinished faces immediately, with the cleaner the adhesive maker specifies.
7. Keep traffic off until the adhesive's stated time.

Common mistakes

Hollow spots and loose boards usually trace back to coverage.

• Spreading too far ahead. Skinned-over adhesive won't transfer.
• Never lifting a board to check. Coverage problems stay hidden until the floor is done.
• Letting adhesive dry on the finish. Urethane is very hard to remove once cured.
• Using the adhesive-only notch when moisture control is needed.

Tools and products we carry

These cover adhesive, spreading and holding boards in place.

• Roberts 1487 Engineered Wood Floor Adhesive
• Crain No. 426 1/4" Square Notch Trowel and Gundlach Versablade Trowel
• Tego 16' Ratchet Strap Clamp
• DriTac Wood Floor Repair Kit for loose boards later
• All trowels and adhesives

References

1. Bostik's BEST adhesive data sheet
2. SikaBond-T55 product data sheet

Linked PDF documents are archived copies saved by PreFloor Tools so they stay available if the publisher moves or removes them. Check the publisher's website for the latest revision.