In order for the flooring to expand or contract with the subfloor, it must be conditioned to the same atmospheric conditions. The grade level is where the flooring will be installed in relation to the ground around the building. Normally, this would be over the basement or a crawl space. An on-grade subfloor is in direct contact with the ground, or over a fill that is in direct contact with the ground. A below-grade subfloor is partially or completely below the ground surrounding the building and is in direct contact with the ground, or over fill that is in direct contact with the ground.
Open time is the amount of time for the adhesive to set before it is covered with the flooring.
Placing sheet flooring into the adhesive too soon may cause the flooring to bubble. Placing tile into the adhesive too soon may cause the tile to move and adhesive to ooze up between the tile joints. Temperature, humidity and porosity of the subfloor affect open time. Working time is the amount of time from when the adhesive is set until the flooring will no longer bond. Working time for tile adhesive is the amount of time from when the adhesive is dry to the touch until the tile will no longer bond.