For optimal performance, what should the surface be covered with when using organic adhesive?

When using organic adhesive for tile installation, it is essential for the surface to be covered uniformly without any bare spots. This uniform coverage ensures that the adhesive can properly bond with the substrate and the tile, providing consistent support across the entire area. If there are bare spots, these areas will not have adequate adhesion, which can lead to tile failures such as cracking, lifting, or detachment.

Uniform coverage helps in achieving a strong, durable bond that is necessary for the longevity and performance of the tiled surface. It allows for even distribution of forces and stresses placed on the tiles, enhancing their overall stability.

The other choices do not provide the necessary adhesion and support. Covering only at the edges or in random patches leaves portions of the surface without sufficient adhesion, increasing the risk of tile failure, while adding additional thickness can interfere with proper setting and drying of the adhesive, potentially leading to issues with the bond strength.