Masonry mortar has a mixture ratio of 1:2.5. Is this ratio volume ratio or mass ratio?

If it is plastering mortar, 1:3 or 1: 2.5 is the "volume ratio".

Mortar is divided into masonry mortar and plastering mortar.

Masonry mortar shall be marked with M or Mb, which has strength requirements, namely M2.5, M5, M7.5, M 10, M 15, M20, etc. Its mix proportion is designed according to the Code for Design of Mix Proportion of Masonry Mortar (JGJ98-2000), and it is generally expressed directly by mass ratio in construction, which is more convenient for measurement.

Plastering mortar is usually expressed as 1: 3 or 1: 2: 3 (that is, "1: m" or "1: n: m"), which is a volume ratio, and there is generally no requirement for strength grade.

Therefore, the mass ratio is used for masonry mortar and the volume ratio is used for plastering mortar. Only in practical engineering, in order to save trouble, the mass of one side is measured first, and then converted into the mass of this volume, so it is generally mistaken for the volume ratio.