How to build a natural stone retaining wall the right way! One tier or more.

My name is Christien R. Stone, I own and operate my landscape and construction company, specialising in natural stone, C.R. Stone Enterprises from East-Bolton, and I've been building stone walls and stone creations my entire life and have found that even some of the educated advise on how to build stone creations is not always accurate. Having built hundreds of thousands of square feet of stonework and handled over a million pounds of stones thus far, you can put some trust in what advice I will give you. Having completed contracts in and around Montreal, all over the Eastern Townships and every where in between, my stonework is still standing and serving its purpose and looks as good as new. So here are my secrets to building a stone retaining wall just for you.

Here are some of the most important things to remember when you're building a retaining wall, which has to actively hold back pressure from behind.

1- The rocks you use combined with the way you use them have to create more pressure resistance than the weight and force on the pressure being applied from behind. Take note that walls near trees may suffer from being moved if they are not a good distance away from the tree (far enough so that the tree moving does not move your wall).

2- The area you're building your wall on may absorb some of your wall's weight making it shift and compromising the structural integrity of your work. Take the time to build a solid base if it's needed.

3- Water collection behind walls is unacceptable to due to the increased load of wet gravel or earth as well as the high risk of heaving due to frost in certain areas, drainage will be discussed.

4- Any multi level tiers should be planned out to ensure top tiers do not add pressure behind levels below them.

5- Finally, your wall should be a part of your landscape that marries well with your home, your tastes, and your life style. Steps can be taken to ensure low maintenance or constant maintenance depending on the layout and final touches you desire.

First step, Your base.

When you figure out where you will want to put your wall, you are going to need to asses the situation that will lie below. And remember that the place you need to put a retaining wall may not be the only place it can go. Moving a wall out a few feet from a bank may allow you to save material by being able to build a shorter wall and keep the same or even more gradual slope behind it. You may simply need more fill. So once you've got your lines marked out where you want your wall, you have to asses the type of material that will lie beneath.

Gravel, which will drain, IF, there are no areas that would obstruct the draining process, would not need much done other than a good compacting with a vibrating plate compactor or jumping jack, depending on the size of wall you're planning to build. And if there are areas that will obstruct the drainage, take care of them by laying a perforated drain tile from the low spot that water will pool in, even if you don't see it on the surface, slopping downwards away from your future wall to an area where collected water will be able to evacuate freely. Don not install drainage towards your house, steps were taken to gather and evacuate water from the edges of your house when it was built, so don't compromise what should work. And now with your gravel base compacted and potential wet spots taken care of. You're ready to start laying your base rocks.

Clay , which will not drain, will need to be either sloped away from the face of your wall and able to drain freely, or slopped downward along the face of your wall so that it may drain through one end. Many landscapers install drains under their walls when clay is found, but this creates an area for water to collect under your wall, which is the last thing you want. If there is no other way to drain water that will collect from simple slopping methods, you can install a drain behind your wall. Far enough behind that your wall will not be resting on the tile, and your base should be slopping very slightly towards to back of your wall to ensure water makes it to the drain and can be evacuated by your installed tile to an area that will never get restricted. Methods to prevent sediment from infiltrating your drain and should be applied to every application will be discussed later.

Earth and other materials , which in most cases are not the most desirable bases for large stone applications to be added on top of, in some cases are acceptable to use as readily available bases. These cases would be; if your area to be built on has been undisturbed for many years and has had time to naturally settle and has an existing slope in front of the area your wall's face will be, if your desired retaining wall will be very short in height and will not force down on its base of any significant amount, or if there is mature lawn under the area that the wall will be placed that has been there for a few years at least which slopes away from the face of your wall, as a well structured lawn is great at evacuating surface water. However, in most other cases, step may want to be considered to ensure your wall will lie on a solid base. If your wall will be higher that around 24" it will apply a large amount of force to the base it lies on over its first few year, causing unstable ground to absorb the weight in some areas and less in others, which will cause your wall to shift or sag and loose its structural integrity. Because of this I suggest de-turfing the area, removing light soil or lawn, and adding clean drainage material. Many other landscapers don't use clean materials, meaning there is no material under a given size, I use 3/4" clean which has only 3/4" stone, and the problem with material that is not clean is that it will tend to create a false base over your problem area by floating on top of existing materials. Clean material, applied in thin layers, then compacted in stages, will be absorbed into existing material which lie underneath, adding to their ability to perform as an appropriate base. In most cases when a two inch layer of 3/4" clean material is added to and compacted to a base area to be built on which is quite earthy, the two inches will easily be driven down into the existing material. Additional 3/4" clean should then be added and compacted to create at least an additional 2" rise from existing levels in front of the future wall face to ensure water can evacuate freely. Do not repeat these practices that I have too often seen. Place a drainage tile under your wall without complete drain preparation, as this will enable water to pool if the smallest shift should occur in underlying terrain and move your wall. Bury your base stones beneath the future levels of your finished landscape terrain which will definitely allow water to gather around and under your base stone and move your wall.

In all cases , you should ensure that your wall will be resting on an area that will be slopping in such a way that water can naturally escape. The face of your wall will have at least 18" of stable ground in front of it as errosion will eat away at areas of the ground in front of your wall should there be a significant slope, about 25 to 30 degrees would be the limit to have a strong 18" of area directly in front of your wall slopping no more than about 10 degrees and any slopes of 30 degrees or more should have a strong couple of feet in front of your wall if you would like it last any amount of time. You have to keep in mind that the weight of your wall will be forcing down on its base, but not only straight down, force will be applied up to a forty five degree angle way from your wall's face, so you have to be sure that there is sound material in that area to successfully accept the load.

Second step, final prep and laying.

Now you're almost ready to start building, you just have to figure out the height of your wall to determine how wide your base area will need to be. For every foot you plan on going up, you want to build your wall as thick in back. If your wall will be over five feet high you can most likely get away with keeping a consistent four to five foot wide wall if you take care of the way your fill stone behind your wall are placed and ensure the wall face is slopping inwards at least 2" per foot of rise. However, if you are going to be building an eight to twelve foot high wall you're going to want to increase the thickness at the the base to at least six or seven feet keeping it consistent until at least half of your height is reached, and then you can start tapering in towards your face up to a two to three foot wide wall at the top. In all cases, your end result at the top of your wall should be around two feet, or a little less if planting will be desired. When you draw a side view of your wall, the triangle you are going to create with your wall should be at least the same size if not bigger than the area behind it from the back of the base up. This amount of weight in the structure of your wall along with a good inward slope and a few laying tricks of the trade, will allow your wall to be able to counteract the pressure from the ground behind it. If you are planning a second tier you should also draw out where your wall faces and backing will end up as well as where the upper wall's weight will be distributed in the area below it. For instance, if you have a four foot wall in front and below a second wall which is only three feet behind the finished face of your first wall, the entire weight of the second wall will be pushing down and out on the center of the first wall most likely causing the center to bow outwards and eventually crumble because the top wall is spreading its load over and area up to forty five degrees down and outwards from its edges. This being known, you should be ready.

Starting with base stone, in brief, these should be some of your larger stone. They will be barring the weight of all other stones above them and behind them. You should also use similarly large stone behind your base as well as behind the center sections of your wall to create a stronger wall which will tie its stone in to one and other. In other words, spread the weight of stones over each other which help them hold each other in place. You do have to make sure, however, that all the stone in your wall are laid level. One stone laid slopping towards another will be forced towards whichever stone it is leaning on by all the weight placed above it, compromising the entire structural integrityof you wall above the area. As well, stones used in the face of the the wall, although may sit flat and level, should not be used should their top be slopped downward towards the front of your wall because the stones placed on top of them will eventually slide off. I have repaired many walls where the previous masons laid just one stone slopping down and out that brought down a complete section of a wall. And the same happens, although not as drastically, when too large of a slope is left slopping inwards to the back and laid on top of. The top stones then force the wedge shaped stone outwards ejecting it from the face of the wall and leaving a hole at best, and causing the entire area above it to collapse at worst.

The trick to getting a wall to last is to tie the stone together, and make sure there is at least 10" of your stone deep in your wall. Which should still be the minimum, and helped by adding strong tie stones behind it. Which means, stones that will essentially be placed like a brick pattern holding each other together by being in contact and forced on by the stones laid above them. So if you happen to com across a long narrow stone that has a beautiful face on the long side, don't do it. Unless you could say this stone is as deep as it is long, it's not worth it. By using the maybe less appealing small face at the end of this type of stone, I call them tie rocks, and letting its length reach deep into the backing of your wall, this stone will tie in to more stones around it and be held in place by more weight from above it, and give you a little faced guarantee of a wall that will last many years. In the Eastern Townships, where I lay wall, many landscaper and stone masons try to save money by laying the faces of the stones which cover more face footage as facing, and I intern end up bringing in more stone in to compensate when I rebuild their failed attempts at long lasting walls. Knowlton, in Brome lake, QC. is littered with hundred year old walls and some dated even further back. My grand father, his father and his father's father had spent their lives building stone walls, and the one thing that you would have noticed about their walls, is that the lasted and are still around. When helping out my grand father one day I noticed the true test of his walls strength, and it wasn't meant to be a test at all. When he laid wall he would pick up great big stone, about 80 to 140 lbs, sometimes bigger, and drop them on his laid sections of wall where he wanted them to go. If you can drop 140 lb stone on your wall in any section that you're building and not suffer any structural damage or movement to the wall beneath, you're on the right path. So remember that the stone you are using have to hold back tons of weight from behind and on top of it, so a wall built out of five pound rocks probably won't fair too well over the years if it is of any height at all. Many of my customer in the Bromont area can tell you about a mason in their area who though he could pull that off.

Third step, ensure your work lasts.

Finally, protect your wall. If you've built a strong wall, there is one last hing that can bring it down, water. Water will end up behind your wall, and as long as your backing remains clean of gravel and earth, it should fair fine. However, if sediment end up infiltrating your wall by being brought in to the backing of your wall by water travelling down and through your wall, it will do two unwanted thing. It will cause instability in the ground above your wall as material is transported through your wall's vacant spaces between stones, especially bad if you have additional tiers above, as all the preparation done to ensure all areas around your wall are sound will be lost and your wall may begin moving inwards, still better that outwards, but may shuffle stones in such a way that causes it to loose strength. The other thing that will happen in colder climates is that the material that gets deposited in to the center of your backing will retain moisture and as this material freezes it will expand potentially completely destroying all of your hard work. I have seen this way too many time when local competition, once again trying to save money on material, back their walls with gravel or dirt. They rarely last a winter without bowing substantially, and quite often simply fall over. In bad cases, a simple rain can cause a wall to crumble when material behind the wall gets heavy and forces out on a wall that has been laid too narrow and with no clean backing. So that's the problem, here's the solution. Geotextile, it may be composed of different materials in different regions, but you want to completely cover the back side of your wall with a product that will allow water to flow through it freely but will not allow any solid materials to pass through it. Thus keeping your wall and its backing clean, with no area which will allow material to disturb the masterpiece you've created. And thinking back to your choice of base preparation, you can now see the importance of getting the water out and away from your wall as there may be a substantial amount collected in the area of your new retaining wall which will act as a drain itself.

Now you can build yourself a great new retaining wall that will last. And remember that a little extra time or money spent the first time around may save you the inconvenience of a needed second attempt.