Strength is not a problem in 90% of the mortar situations. The important factors are workability and compatibility with the masonry units. Permanent exposure is not as much a problem as variable exposure. Most streams have variable water levels and flows.
What type of stone and how long will the mortar have to cure before immersion? Hard, low absorptive stones (usually igneous) are difficult to bond while most sedimentary stones, and older have different requirement long long term durability and compatibility.
What size and shape of aggregate? - Smooth, irregular or jagged? That affects the strength of a mortared structure.
ASTM C270 lists a number of mortar types (Types M, S, N, O, etc.) based on the materials and needs. They also recommend the lowest strength possible to carry the structural loads to enhance the other properties/benefits of the mortar.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
The stone is limestone and the approximate time for the lake (creek)to be refilled will be around one week. As for the variation of temperature, the water is mostly kind of stagnant, doesn't have aggressive flow. freezing temperatures here in Texas don't last too long. I'm planning to use type "S" with a strength of 2000 psi.
Alfred....water leaches calcium from mortar, thus reducing its strength....use a high strength mortar for this application. Standard strength for Type S is 1800 psi. Type M would be better for this.
