Stone Wall Restoration
Here in New England a common request that we receive is to do stone wall restoration, or to rebuild existing stone walls. Most commonly these are drystack retaining walls that have deteriorated over time and need to be taken down and rebuilt. Fortunately the stone is perfectly re-usable, so stone wall restorations are comparatively less in cost than building new.
Why do stone walls need restoration?
In our experience the stone walls built in this area within the last 100 years or so were done without much attention to base material, backfill, or drainage. When we dismantle older stone walls, what we usually find is dirt backfill mixed with stone. Dirt or soil does not drain well, it holds moisture and will expand with freeze/thaw cycles. Soil also promotes plant growth and invites vegetation and roots.
Soil erodes and overtime will rinse through the stones towards the front of the wall. As it mixes with the face stones, the freeze/thaw and root growth will cause more and more movement in the stones. Eventually stones fall off the wall, plants and soil show through the front, and/or portions of the wall collapse altogether. At that point there isn’t much one can do to repair the wall other than dismantle the wall (or just a section) and rebuild.
Fortunately the stones can all be re-used, and a rebuild poses a great opportunity to re-design the walls in a favorable way. This will often mean pushing the wall back to create more space, raising the height to create more level ground above, adding stairways for access, etc.
Below are photos of various walls that show the conditions before restoration. As you can see, these walls are not the most visually appealing, and some of them are starting to deteriorate or collapse.
Restoring the Wall:
Excavation + Prep
To restore a fieldstone wall we first dismantle the wall and save the existing fieldstone. The stone will go into a pile nearby while we excavate the base and backing. For the base we make sure to excavate deep enough until we find solid/well draining subsoils. We then compact the subsoils and add a layer of compacted crushed stone to set our base stones in.
Behind the wall we excavate far enough back provide room for clean stone backfill. A general rule of thumb is that the thickness of the wall should be at a very minimum 1/2 of the height. But more width is better whenever possible. At the back of the excavation we install heavy duty filter fabric. This is a construction grade fabric that allows water to flow through but does not allow dirt or roots. This means dirt/plants will never migrate or mix into the backfill or wallstone.
We haul away excavated soil or stockpile on site for grading behind the wall. Often in restoring a stone wall we will raise the height to achieve a more favorable grade behind and so saving the fill is useful.
Take a look at the following stone wall restorations in various stages of excavation or prep:
Building The Wall:
To build the wall we start with the largest stones and set the base course. These stones are the heaviest and sturdiest and form a solid foundation on which to build the rest. Next we stack up the face. We build the face of the wall by carefully stacking the stones with the bulk of the stone tying back into the wall. Each stone should be stacked on top of the joint below for added strength. Additionally, we use smaller stone or “pinning” to shim and lock the stones in place. We backfill with more fieldstone, rubble, smaller stones, etc. We don’t use gravel or crushed stone behind the wall because it is too small and can flow or erode through the face of the wall. We want our backfill to be tightly packed stone or rubble that is solid, adds mass to the wall, but drains water freely.
In most cases, all the material we need to bring to the site is a bit of crushed stone for the base, and additional backfill to replace any dirt we have removed. We may also bring supplemental fieldstone to mix in with the existing. This is necessary whenever the wall may be increasing in size.
As we reach the desired height we stretch a cap line, and use our largest, flattest stones for the top. These large flat stones help hold everything in place, and give the wall a clean finish. The result is a sharp looking and long lasting New England stone wall.