What it does
Adhesive is spread with a notched trowel whose notch size is specified by the adhesive manufacturer for the board being installed. The notch meters how much adhesive goes down; too little and coverage fails, too much and the board floats on it and squeezes up through the seams.
Modern flooring adhesives are moisture-cure urethanes, and many double as a moisture barrier rated to a stated slab RH. That rating is the number the in-situ probe reading is checked against before anything is ordered.
Open time matters as much as coverage. Adhesive spread too far ahead of the boards skins over, and a board laid into skinned adhesive is a hollow spot from the day it goes down.
Why it matters to your floor
- Glue-down is the assembly for condo slabs and for anything over radiant, which is a large share of the GTA market. It is also the assembly where the failure is worst: a delaminating glue-down floor cannot be repaired in place, it comes up.
- Herringbone raises the stakes again, because a pattern field has far more end-grain joints per square metre and coverage matters more, not less.
What happens without it
A general-purpose adhesive chosen on price, the wrong notch, or spreading half a room ahead of the crew.
Hollow spots underfoot within a year, and eventual delamination that is not a repair — it is the floor again.
How to tell, before you sign
- Ask which adhesive, by name, and what slab RH it is rated to. Then ask what the slab actually read.
- Ask what trowel notch that adhesive specifies for your board. A shop that knows the answer has read the data sheet.
These questions are meant to be asked of everyone quoting you, not only of us. A trade that cannot answer them is telling you something useful.
The method it belongs to
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