Retaining Walls Build a Drystone Retaining Wall
by Raymond Alexander Kukkee
© 2009 by Raymond Alexander Kukkee
Build a Dry-stone Retaining Wall
Natural dry-stone retaining walls have a special appeal to the environment and homeowners alike. No two natural stones are identical, colour of stones vary, and any structure built of natural stone offers solid, permanence with high curb appeal.
The dry-stone retaining wall may have been the first form of retaining wall ever built for convenience sake. Natural stones of all sizes right on the site are commonly used in dry stone construction. The reasoning is simple; natural stones often need to be removed for other reasons. Rock is heavy, and logic dictates that the closer stones were at hand, the more likely they were to be used in any adjacent dry-stone wall, fence, or other structure being built. A dry stone wall can eventually be closed with mortar or plants such as ivy and flowers can be added to soil pockets for a spectacular focal point for your wall.
In modern times, other materials are available and easily obtainable, but why import expensive timbers and other materials to build a retaining wall if you have an abundance of free natural stone? Do you have a steep slope or area that would benefit from a structural retaining wall? Little has changed in dry-stone wall construction over the centuries; the idea is to use what you have. You can build a thing of beauty using much of that rock and a few handy tips.
You will need to formulate a plan. Make a sketch and lay out the location of the retaining wall with small pickets.
**Note: Are any gas lines or other services in the area that could be damaged by digging? Call first, to prevent a serious problem.
Is a building permit required? Where are your lot lines? How high will it be? Can the area be terraced with more than one wall, making the walls lower, safer, more stable, and easier to build? Are very large rocks involved? Plan to obtain the service of a loader or backhoe to do the heavy lifting.
Because a dry-stone retaining wall is a loose structure constructed using no mortar, the stones must lay securely and remain stable as piled.. Keep in mind that flat-shaped stones, or split sedimentary rock such as limestone, sandstone, slate, and other layered, or bedded rock is much easier to pile and work with, and does result in a safer, more stable structure.
You may need help lifting even moderate sized rocks. Rock is heavy stuff, so plan your lifts carefully and logically. Use lifting equipment where necessary. Caution: Rocks that are block-shaped, sub-rounded or rounded can roll downhill and may cause injuries and wreak havoc, so be careful. Building with rounded stones takes extra care. Never store rounded rocks on a slope for your project. A rolling boulder can easily cause serious personal injury.
You will also need the following:
- Safety glasses and leather gloves
- A rock hammer and chisel, or rock saw (optional)
- A carpenter’s line and pickets
- Gravel, free-draining, containing no roots or big cobbles,
- A gasoline-driven mechanical plate packer if available
- A backhoe or loader if determined to be necessary
- Rocks: Flatter stones are preferable. Rounded rocks are more difficult to lay up and may require a different design, depending upon conditions.
Establish the Footing or Base:
If the soil condition on the site is stable, level and very hard or stony, a dry-stone wall can theoretically be laid directly on the surface, but in the majority, a footing, or base should be established. In areas of deep frost penetration, severe heaving of the soil and any structure can occur, destroying the wall, so plan accordingly. Using pickets and a line, establish the outline of the required base or footing, which in soft soil conditions should ideally be an absolute minimum width of three times the thickness of the wall. Excavate all soft soils and fill the trench with a minimum of 6″ of crushed rock or gravel that will pack firmly. Water the base and use a rented plate packer to pack the gravel if available. Level the gravel and pack the footing firmly.
Laying Up the Dry Stone
Lay up the first layer or row of stones to a line established on the visible or front side of the wall. Use the largest stones available for the first row, and place them as closely as possible to one another. If only smaller rocks are available, use similarly sized rocks to build the thickness of the wall desired. Install the second course with the stones straddling the joints between the stones on the first layer, as is standard practice in masonry; Two over one, and one over two for strength.
Ensure adequate Drainage:
If soil conditions are wet, install a perforated drainage tile on the back side of the bottom course level with or just below the top of the footing. Always place the pipe with the perforated holes facing DOWN to allow water to rise and enter the pipe without carrying soil and fines into the pipe which can cause premature failure of the drainage system. Locate the discharge point on the ends of the pipe clear of the bottom course to ensure drainage water does not wash away the footing at the discharge point.
Build the wall Higher
Back fill the first two layers with free-draining gravel and on top of the drainage pipe and pack it firmly. Establish the third layer of stones, back setting them marginally to ensure the front face of the wall is leaning back into the hill marginally for stability, especially if the wall is to be more than two feet in height. If individual rocks do not sit firmly and solidly, use the rock hammer to knock off rough layers or small pieces, saw portions off, or install flat pieces of stone or smaller rocks of all sizes as wedges as necessary to stabilize the seating of the individual rocks, eliminating all instability or motion.
*Note: if the soil on the hillside tends to slump, or slide down hill constantly, consider installing geo textile in the wall construction, or install a deadman anchor in the wall for strength. For dry stone construction, bury one or more treated timbers or railway ties parallel to the wall deeply in the up- hill side, fastening a galvanized cable to the timber and anchor it to a large rock in the wall using rock anchors. Ensure there are several layers of rock over the anchor cable.
Continue with each subsequent layer in the same fashion, back-filling with free draining gravel or coarse sand as you proceed. You may fill the gaps between the rocks on the face of the wall with soil if so desired .
To Complete the Dry Stone Wall
Make the top course as flat and level as possible by selectively choosing appropriate rocks, and backfill the wall to just below the top with free draining gravel. Fill the last few inches using topsoil and establish the grade desired. Rake and seed the topsoil, and establish ivies and other ground-cover plants in the gaps between the rocks if desired for a unique, beautiful effect.
What about building walls with Rocks that are Not Flat?
In a location where only rough, or rounder, chunky natural rocks are available for use in a retaining wall, a wall of a different character should be built. Typically it must lean back at into the hill at a sharper angle to be stable. The angle should ideally be no more than 45 degrees for stability. Much patience is required to fit walls of this nature together and end up with a solid, secure wall. .
Establish the footing and drainage in the same manner as above, and line up the first row of the largest rocks available. Backfill the layer to slightly above the level of the first row of rocks, and lay in the second row of rocks, ensuring that each rock is stable as it is seated, being firmly supported by the backfill material and the two rocks beneath it. Again, backfill with free draining gravel, fill gaps if desired with soil, and proceed to the next layer, repeating the process. Remember, this type of wall should lean into the hill substantially for stability.
The first impression and appearance of a drystone wall can also be approximated on a moderate slope or even a flatter angle by excavating soil adequately to place the bottom half of a large rock into a customized cavity in the soil, and repeating that process for all of the rocks along the length of the wall. For the second row, backfill and excavate similar holes for each rock for the second row, ensuring that each rock so placed is seated directly on the two rocks below it, and supported securely from behind by a backfill layer of free-draining gravel.
This type of slope stabilization is not highly recommended where there is serious water runoff potential on the surface, as the majority of the weight of the rock is resting upon soil that may be washed away by erosion.
Building with rock can be so interesting you may want to beg some of those annoying rocks from your neighbours. When you build your own dry stone wall, have fun and be careful. Happy building!