How to Calculate Mortar for a Rock Wall on a House

One of the first steps to any project is determining the amount of necessary materials. A rock or stone project requires rock and mortar. Acquiring the proper amounts of both materials is critical to preparing the job site for the project. Making accurate measurements and using some basic rules of thumb can help calculate the amount of mortar necessary.

Things You'll Need

• Tape measure

Instructions

1. Measure the wall area where you plan to apply the rock. Measure both the height and width of the area. Make the measurements in feet and round up to the nearest foot before making the calculations.

2. Calculate the area of the planned rock wall by multiplying the height and the width. For example, if the wall is 10 feet long and 8 feet high, the area of the wall is 80 square feet. Subtract the area of any doors or windows in the wall. Add together all the walls involved in the rock or stone project.

3. Divide the total area of the project by the coverage for each bag of mortar. For example, Type S mortar covers about 15 square feet per 80-lb. bag. In this case, an 80 square foot wall would require between five and six bags of mortar. Purchase six bags of mortar to allow for waste.

Tips & Warnings

• Different types of stonework require different amounts of mortar. A stone veneer of precast stones uses less mortar than a natural stone wall. Veneer walls also use a different type of mortar than other types of stone projects. Consult the manufacturer’s instructions for the proper mortar and the expected coverage.

• Use stone mortar within two hours of mixing for best results. Apply the mortar over metal lath, a wire mesh fastened to the wall, before applying rock to the mortar.

References

• Rogue River Stone: Estimating Materials
• Spec Mix: Stone Veneer Mortar