How Much Mortar Is for a 130-Foot Fieldstone Wall?

The Surface Area of a Row

• Each row of a wall needs to be the same size as, or smaller than, the row beneath it to ensure stability. Measure the width of at least 10 of the largest fieldstones that you have. Add these widths and divide by 10. This will give you an idea of the average width of the stones. Express the average in feet for computation: If the average width is 18 inches, then that should be expressed as 1.5 feet. If the average width is 9 inches, then that should be expressed as .75 feet. Multiply the average width by 130. Now you have the surface area of a single row in square feet.

Mortar Volume Between Rows

• Each row needs 3/8 inches of mortar between it and the row beneath. That is equal to 0.03125 feet. Multiply 0.03125 by the area of a single row to get the volume of mortar in cubic feet needed between the rows. You will actually need more than this to lay a row, as you have to put down 1 full inch and then press the stones down until the excess is squeezed out. However, you can reuse that excess.

Stones Per Row

• Measure the lengths of several of the largest and smallest stones and average them together, just as for the width. This will give you the average length of the fieldstones. Make sure that this measurement is in feet. Divide 130 by this average length. The result is the average number of stones each row will take.

Mortar Volume Between Stones

• The stones within each row also need 3/8 inches of mortar between them. Measure the heights of several of the largest stones and the smallest stones. Average them together just as you did for the width. The result will be the average height of the fieldstones. Multiply the average width, in feet, by the average height, in feet. Multiply the result by 0.03125. This result is the volume of mortar you need between two average stones. Multiply the result by the number of stones in the row to get the volume of mortar you need between adjacent stones for each row. Add the total amount of mortar between stones in a row to the total amount underneath the row to get the total volume of mortar needed for each row.

Total Mortar Volume

• All that remains is to determine the number of rows in your wall. Divide the height that you intend to make the wall by the average height of your stones, in feet. The result is the number of rows you will need to make. Never build a stone wall higher than 4 feet without special training as an engineer. Multiply the total volume of mortar for a single row by the number of rows to get the total amount of mortar you need for that 130 foot stone wall.