How to Mix Mortar for Cast Stone

Mortar spread on a stone surface in order to apply cast stones.

Creating a wall using cast stone requires a strong, resilient mortar that retains enough flexibility to withstand movements in the stone surface without crumbling. Prepackaged mortars often fail to meet the necessary standards, so mixing your own is the best path to success when building with cast stone materials. It's not a difficult mixture to create, using Portland cement, sand, lime and water. However, you'll need to mix the materials in the right order and in the correct ratio. After mixing, though, you can apply the mortar where needed, resting assured that the bond created will hold the stone firmly in place for decades to come.

Things You'll Need

• Washed masonry sand
• Portland cement
• Lime
• Color pigment
• Mixing container
• Electric drill with paddle bit attachment

Instructions

1. Set aside the materials necessary to create your cast stone mortar. The proper mix by volume consists of six parts washed masonry sand, one part Portland cement, and one part lime. You can also use a color pigment as long as it weighs less than 5 percent of Portland cement used in the mixture.

2. Pour the sand into your mixing container and then add any coloring pigments used. Add the lime and Portland cement to the mixture, and then begin to add the water. Mix the combined materials with an electric drill with paddle bit attachment while adding the water for about six minutes, until you have a mortar the consistency of peanut butter.

3. Use the mixed mortar immediately, wetting down the cast stone slightly before applying the mortar to prevent the stone from leeching out the mortar's moisture. Throw out any mortar remaining after 90 minutes as it has set too much to create a solid bond between cast stone and subsurface.

Tips & Warnings

• Wear a respirator, safety goggles and work gloves when mixing or applying the mortar to prevent harm from the strong chemicals used in the mix.

References

• Cast Stone Institute: Mortars

Resources

• Cast Stone Institute
• Traditional Building Magazine: Product Report -- Cast Stone Architectural Elements