Calculations for Stone Walls

Gravel

• The first layer that goes down for any stone wall is the drainage layer of the foundation. This is usually gravel or crushed rocks that are in gravel form. The gravel is packed down into the dirt within the excavated area for the foundation of the wall, and is usually 6 to 8 inches, depending on the height of the wall you are building. This keeps the soil from retaining water, which would cause the wall to buckle in the winter when the water freezes.

Sand

• On top of the gravel, is a compacted layer of sand or stone dust. It needs to be between 2 and 4 inches thick after it has been compacted, which means you actually need to order more than you think you need, because some of the sand will fall down into the compacted gravel. After you have a 2- to 4-inch thick layer of compacted sand you can set the stones for the wall, with the sand acting as a compression layer to help the wall settle slowly over the years.

Extra Material

• Whenever you are making calculations for the actual stone for the wall you need to order at least 15 percent extra to be on the safe side. Many professionals prefer to tag on 20 percent rather than 15, especially in the case of natural stones that are being broken down on site to fit into the wall. This extra material is known as waste material and is there in case you need several attempts to get a stone cut or broken just right to fit around a window or other termination points.

Mortar

• Your stone wall might not require mortar, but if you do, you have a variety of choices. You can use just enough mortar to stick the stones together but not enough to show through the finish surface, or you can have grout joints in which the mortar is a half inch or to three-quarters of an inch thick around each individual stone. You can use a mortar calculator to determine how much mortar you need or check the back of cement mix bags sold in home improvement stores for square footage coverage amounts.