Stone Walls: Dry vs Wet

Dry vs Wet laid Stone Walls:

One of the first questions many homeowners ask when proposing a new stone wall is whether the wall should be built with or without the use of mortar.  (A “wet” stone wall uses mortar, while a “dry” stone wall does not). Different factors can effect this decision, but we at Concord Stoneworks will most often recommend a dry stone wall.  In this article we will discuss why this is so and the advantages and disadvantages of either option.

split face stone wall

Mortared Stone Wall – Split Face Stones

A wet stone wall is designed as a rigid structure.   When external forces are exerted on the wall, (ground settling, frost heaving, errant snow plows, etc.), the wall is designed to withstand the forces and hold its form.   A well-built, mortared stone wall with a solid base and backing will hold up for quite some time, yet, it is inevitable that at some point movement will occur. When it does, and when the forces become too great for the wall to withstand, the material cracks. When this occurs the repairs are not easy. Patchwork will be unattractive and do little for the structural integrity. Rebuilding the wall or portions of it will be labor intensive and may require all new material.

On the other hand a dry laid stone wall is flexible. Water drains through it naturally, and any minor settling or shifting that occurs is absorbed by the wall and goes largely unnoticed. Even if major failure does occur for some reason, the wall or portions of it are easy to dismantle and rebuild using the same material.  Repaired portions will also blend seamlessly into the existing wall.

Drystack Stone Wall - S. Windsor, CT

Drystack Stone Wall – S. Windsor, CT

One of the advantages of a mortared stone wall is that it is easier to achieve a high level of finish. While building the wall, the mason can rely on the adhesive properties of the mortar to hold the stones in place. This makes it easier to focus on facing the wall to create a very flat and consistent finish.

A dry stone mason uses gravity only to hold the wall together.   Each stone is laid with structural integrity in mind. Instead of facing the wall with a stone’s flattest face, the stones are stacked so that the heft of the stone ties back into the wall and holds everything together. This produces a more rustic or traditional look. Extremely high finish dry stone walls do exist, but they take extra time and care to produce.

Lastly and most importantly, it is often less costly to build a dry stone wall. Wet stone walls require a rigid concrete base, mortar for the wall and the machinery/labor to mix the mortar, and proper drainage.  This additional prep work is necessary to try and prevent any movement.

Dry stone walls on the other hand are built with a simple gravel base and backing. They require no additional drainage and the only material needed is the stone itself.

Dry stone walling is a unique skill that not all masons fully understand and appreciate.   Although there is a time and place for wet stone walls, we at Concord Stoneworks much prefer the aesthetic, function, and efficiency of a dry stone wall.


Bluestone Walkway and Granite Steps – Boxborough, MA

At this home in Boxborough, MA an old bluestone walkway had come out of level and the stones were breaking apart.  Also the bluestone steps had come loose and were unstable.  The homeowner wanted to replace the walkway with new bluestone and use solid granite steps.

For this project we removed the existing bluestone and excavated below.   Whenever possible we will excavate by hand in order to preserve the surrounding landscape and minimize/eliminate extra costs for sod repair that can arise when machines come in.

Here we have excavated the area to depth of 8-10″ to allow for new base material.  The new walkway will go in the same footprint as the old.


excavated stairway


excavated walkway

Next we install the granite steps.  The steps are dry laid on a bed of crushed stone and a thin layer of stone dust to achieve level.   One step goes in, we back fill behind it to meet level, and the next step is stacked on stop.  The adjacent wall has to be partially dismantled to make room for the new steps.


granite step installation


granite step installation

All nine granite steps are set.  With the steps in we have a guide for the level of the walkway portions.  We’ve carefully planned the upper steps so that the finished height of the walkway doesn’t sit too high above or too low below the grade of the adjacent sloping lawn.


granite step installation

Next we finish compacting the subgrade and filling the base with crushed stone to prep for the bluestone walkway installation.  The crushed stone provides a solid base that readily drains water.   A layer of stone dust is used to set the bluestones in and achieve the fine tuned level.


bluestone walkway prep

The bluestone is installed, stone dust is swept in the joints, and some soil is added to the edge to regrow grass and meet the level of the stones.  The bluestone used is natural cleft, full color range.  It comes with it’s irregularities, but produces a handsome and slightly more rustic finish than the more finely treated varieties of bluestone.


completed bluestone walkway and granite steps


completed bluestone walkway


completed granite steps

Phase I – Stone Retaining Wall – Westford, MA

The first phase of this project was to clear the hillside and rebuild the retaining wall.  As discussed briefly in the project overview, the original stone wall had been built poorly.  The builder dry laid the fieldstone directly on the clay subsoil, carefully faced the wall without giving much attention to structural integrity, and then mortared the top course to achieve a clean cap.  This method was neither here nor there.  A properly built dry wall can be laid right on the ground.  If the stones are stacked for strength and tied back into the wall, the stones will settle with ground movement but remain structurally sound.  And if the wall doesn’t have a perfectly clean face and cap to begin with, visually the movement will go unnoticed.


original stone retaining wall

If the finer finish is desired, however, the builder should have laid a sturdy base for the wall to minimize ground movement and then mortared the entire wall so that it was one rigid mass.  In this way the wall resists ground movement and other forces.  This method takes more preparation but is an easier way to produce a finer finish.  The downside is that when/if the forces become to great for the wall to withstand, the mortar will crack and the effect will be very noticeable and difficult to repair.

Fortunately since most of the wall was dry laid, the stones were still clean and we were able to reuse them to build the wall.  Our plan was to tear out the entire wall, lay a gravel base, and dry lay the stones with a focus on structural integrity.   The gravel base serves a couple purposes in this case.  First it provides drainage for the wall.  It lets water drain down away from the wall stones, and if any freezing occurs there is plenty of flexibility and air space in the gravel to take up the movement.  In this case the gravel base also provided a drainage channel for the whole hillside.  As water runs off the hillside, it will settle in the low channel beneath the wall.  And being that our channel was sloped towards the lower end of the property, the water will gather and flow down and out to serve as part of our drainage system.

Here we have cleared the hillside of the larger trees and brush.  It’s a nice looking wall, but sadly it’s been undermined in too many places and has to come down.


original hillside + wall

Here we are clearing the rest of the hillside with the machine.  The wall stood up to it’s weight for a little while and then…


hillside clearing

The stone wall collapses and we dig out the rest of it:


the wall collapses


excavating the wall

The wall is fully excavated.  As it turns it was laid over 4′ thick.  That’s a lot of stone to deal with, but, it turns out to be quite useful for the rest of the project.


excavated wall


100-150 tons of stone

After the wall is excavated our suspicions are confirmed that the subsoil is in face almost solid clay.  Clay does not let water percolate, and when it saturates it stays wet for a long time.  With some well timed rain, our trench fills with water and we get a good look at what’s been going on behind the old wall.

With the trench sloping downhill, we fill the gravel base, and then lay the base course of wall stone.  The wall now has a solid base to sit on, and there is a drainage channel below it to send runoff down hill and away from the front yard:


gravel base


base course of wallstone

Now the rest of the wall can go together.  We lay the stones stack style so that the stones extend back into the wall and only the small face shows.  The machine helps with the larger stones and much of it is done by hand.  After a week or so of hard work the wall is coming together:


rebuilding the retaining wall


rebuilding the stone wall

The wall is for the most part complete.  There is some extra stone that we will be able to use for the next portion of the project.   The next portion being a dry stream bed that will pick up the water flow at the end of the wall and carry it down and around the side of the property.


fieldstone retaining wall – Westford, MA


fieldstone retaining wall, Westford, MA