Natural Stone Retaining Walls
Natural stone walls are retaining walls constructed from cut stone without the use of mortar or other adhesives to hold the wall in place. Instead, the wall is held together by friction and the weight of the stacked stones (Homestore.com, 2000).
Kallin Johnson, 1997, Granite blocks
Natural stone is a popular alternative to the traditional modular cement block for retaining wall construction. Dry-stacked, natural stone walls add a very natural look to any landscape as the material is taken right from the ground. Natural stone walls allow water to flow freely behind and through the wall thus relieving a significant amount of pressure on the wall.
- Natural stone is a generic term for any quarried and cut stone that is used for construction purposes. The actual types of stone include granite and various kinds of limestone which all have slightly different aesthetic differences.
- Granite is a reddish stone with lighter and darker aggregates within. It is best for larger walls, as it is heavier than limestone, which allows it to withstand more weight. Granite will split more precisely than any other type of wall stone.
- Limestone is light in color and is not a heavy stone in terms of weight. There are also various types of limestone. Fond Du Lac limestone is a very white stone and has a uniform shape. Chilton limestone has blue and red tints to it but has more imperfections from splitting than most stones. Limestone costs less than granite.
- See "Constructing Flagstone Steps in the Landscape" for more types of stone.
- The size of stone varies greatly. Wall stone can be packaged and delivered in a specific range of sizes. Common heights would be 2-3 inches, 3-4 inches or 4-6 inches. The width of the stone (from the face to the back) is sold at 6", 8", 12" 18", and random sizes.
- A general rule of thumb is to use bigger stones for a bigger wall. Walls that are under 18 or 20 inches could be constructed with stone as small as 2" X 6". If a wall is over 20 inches, it is best to use 4" x 8" stone or larger (Nutting, 2002).
- Walls can be built with straight courses (walls with rows of stone running the length of the wall),
or they can be built with random courses (walls that have rows of stone that are interrupted after a few feet).
Blue Mountain Building Stone Company
- Stone requirements per square feet of wall face:
Width Sq. ft. per ton 6" 30 8" 20 12" 15 18" 8 Random 15
- According to Brett Nutting of JLM Landscape, natural stone walls should not be taller than five feet. If a taller wall is required, it is recommended that the wall be terraced into two or more smaller walls or use a different type of wall material, such as cast concrete block walls. Consult the SULIS Implementation Report on Installing Block Retaining Walls for more information.
- Safety equipment: goggles, gloves, steel toe shoes
- Shovels: both spades and flat shovels for excavating and backfilling walls
- Marking paint or something to draw the wall shape on the ground
- String line and stakes
- Stone splitter
- Retaining wall stone
- Crushed limestone
- Pea gravel, 3/4 inch clear limestone, or other drainage aggregate
- Large rubber mallet
- Tape measure
- Skid loader: optional but may be necessary for large walls.
- Geo-textile fabric
- Plate compactor
- Drain tile
- Using the tape measure, string line, stakes and marking paint, measure and lay out the wall. Use the string line and stakes to mark off any straight portions and the marking paint to draw out any curves. As curves become tighter, smaller stone will be needed. It is best to keep curves as large as possible.
NOTE: When curved walls are desired, is important that the curves be as large as possible to eliminate jagged curves. Additionally, smaller pieces should be used around curves. Larger pieces will create flat spots on the curve and the set backs from one course to the next will not be even.
- Dig a trench that follows the string line and/or marking paint. The trench should be 1 foot deep by 6 inches wider than the stone. For instance, if the stone selected is 8 inches wide, the trench should be 12 inches wide and 12 inches deep.
- Fill the trench with 3-4 inches of crushed limestone. Make sure that the limestone is roughly level and compact it thoroughly with the plate compactor. Add another 2 inches of crushed limestone on top of the compacted limestone
- Begin leveling the base course of stone by placing a stone on the crushed limestone. Check for level front to back and side to side and adjust accordingly with the large mallet. Due to the nature of the material, the stone will not be perfectly level, but it is possible to be very close. Once the first stone is level, continue along the trench making sure each new stone is level with the preceding. Use the string line again to make sure the straight sections are straight.
- If the wall is going to be larger than 3 feet high, perforated drain tile should be placed behind the base course and then buried by the drainage aggregate. An illustration of drain tile may be found in Step 7 of this report of Step 6 of Installing Block Retaining Walls.
- Next, stack the second course on top of the base course. Make sure the seams between the stones do not line up from one course to the other. Also, pick stones that fit well with those on either side. If there are large gaps, it may be necessary to use the stone splitter to get a more snug fit. Additionally, each course should be set back at least 3/4 inch to allow the wall to lean back into the ground that it will be retaining. Oftentimes the stones will not lay perfectly level on the preceding course. It is then necessary to shim the backs of the stones to eliminate wobbling. Shims are small flat chips that break off the stone when they are split.
- After two or three courses are stacked, backfill the wall with the drainage aggregate. To do this, lay the geo-textile fabric on the soil behind the wall, and dump the drainage aggregate between the wall and the fabric. The aggregate should be at least 8 inches from the wall to the fabric. Compact the aggregate thoroughly with a shovel or large mallet. It may be necessary to fill dirt in behind the fabric as the stone is added.
- Continue to alternate stacking 2 or 3 courses and backfilling the wall until the wall is complete.
Blue Mountain Building Stone Company. June 2002. http://www.bluemountainstone.com
Brett Nutting. Vice-President JLM Landscape. Feb. 20, 2001. Interview
Buechel Stone Corp. 1998. Pamphlet
Dixie Stone & Marble, Inc. 1999. "Landscape Stone."
Homestore.com. 2000. "Building a Dry-Stacked Stone Wall." http://www.homestore.com
Kallin Johnson Monument Co. 1997. http://www.kjgems.com/
Vengeance Creek Stacking Stone. 1998. Product Listing. http://www.vcstone.com/information.html
This implementation report was developed by Chris Matson, student, University of Minnesota Department of Horticultural Science.