A Guide to Installing a Concrete Mow Strip Under Fences
Whether you are planning a new fence or have an existing one, it’s not uncommon to wonder if a concrete mow strip under your fence is a good idea – and how they work.
Lets take a closer look at what concrete mow strips are, why they are used, and how they are installed or constructed.
Why Are concrete Mow Strips Installed Under Fences?
You might think you already know why concrete mow strips are installed under fences, but there are actually a few reasons why these mow strips or concrete aprons, as they are sometimes known, are used for various types of fences. These include:
- To allow for mowing of grass near fences and prevent grass growth under fences – often used for sites like parks and sports facilities
- To prevent digging under fences by people or animals – usually for higher security fence projects
- To prevent vegetation growth along electric fences – vegetation can cause false alarms on managed electric security fences, so preventing growth is important
- In areas with high rainfall, when sloped correctly, ensure that water drains away from the bottom of your fence
There might be any number of other reasons why you might be considering a mow strip or fence apron, and they are a very versatile addition to any fence specification.
Are Concrete Mow Strips Under Fences Done During Construction or After?
The easiest way to construct a concrete mow strip along a fence is to do it while the fence is being erected.
Placing and stripping formwork and placing and smoothing concrete is a lot easier when the only thing you have to work around are fence posts!
However, depending on the design of your fence system, it may be possible to do this after your fence is completed too. Your fence company will probably charge for additional labour when it’s done this way, though, as it tends to take a lot longer!
How Are Concrete Mow Strips Under Fences Constructed?
There are various options and designs you can choose when you construct a concrete mow strip under a fence. They can be different thicknesses and different widths, and they can be symmetrical or asymmetrical, where one side of the mow strip is wider than the other. However, most concrete mow strips or concrete fence apron slabs share a few common traits:
- They’re usually not reinforced because they are not load-bearing – they are cast around the fence, but they don’t carry any of the fence’s weight
- They usually extend a few inches into the ground and usually an inch or two above the ground
- They are cast in place using formwork, which is relatively simple to place and strip
The easiest way to cast a concrete mow strip along a fence is usually to trench for the concrete before you install your posts or even dig or drill your holes. Then the posts are placed and cast up to the surface of the trench, and then the formwork is placed, and the concrete mow strip is cast.
Most concrete mow strips along fences will be angled slightly away from the fence to ensure that water runs away from the fence, so there is usually some work to be done once the concrete is poured. This is definitely a job for more than one person!
Expansion Joints In Concrete Mow Strips
If you live in a hot area, you’re probably very aware of the expansion of materials in the summertime. Concrete is no different. When it gets hot, it will want to expand.
The problem is that if your concrete mow strip is cast in one continuous piece, there will be nowhere for that expansion to go and that usually results in cracks and damage.
To prevent this, you can add an expansion joint once every few fence panels. These could be as simple as a saw cut in the concrete, or you could use something like polystyrene or soft board to create a filled joint that can still compress when necessary.
Void Form for Concrete Mow Strips
At the other end of the spectrum, if your concrete mow strip is constructed along a fence in a colder climate, where the ground often freezes, you might have an expansion problem in a different direction.
When soil (or, more importantly, the water in the soil) freezes, it expands, unlike most other materials. When you have something like concrete on top of that soil, the result is the same as it would be from expansion in the heat – the concrete cracks and deforms.
One solution to this is to cast your concrete mow strip on top of what is known as “void form.” This is a preformed material that is designed to be placed under the concrete and has voids that allow deformation when the soil expands. So, instead of your concrete deforming and cracking, this flexible void form material will deform and then return to its former shape when everything thaws again.
How Much Does a Concrete Mow Strip Under a Fence Cost?
As with most things in the fence world, cost is always a factor when considering adding a concrete apron or mow strip to your fence.
However, also as with most things in the fence world, this really does depend on many different factors, including whether you’re installing it on a new fence or an existing one, how wide and thick it will be, what concrete strength you plan to use and various other design features and site-related factors.
The best advice, if you think you want a concrete mow strip on your fence, is to ask your fence contractor or fence company to quote that feature as a separate item on their quotation. Then you can decide if you want to go ahead or not.
Do All Fence Companies Do Concrete Mow Strips?
Another common question in the fence world, and another one where the answer is no.
While many fence companies will be willing to install a concrete apron or mow strip along your fence, others will not. The only way to be sure is to ask them when you contact them for a quote.
