Can You Use Mortar to Set Fence Posts?


Sometimes, you have an extra bag of mortar laying around from a previous job and you would like to use it and be rid of it taking space in your garage. As fate would have it, you need to set a fence post or two to repair a section of your fence. Is it a good idea to use that mortar to set your fence posts?

It is definitely possible to successfully set fence posts using mortar, although concrete is ideal for fence posts as it gives it longevity not found with mortar. When using mortar, mix it with gravel or other small stones to give it more strength.

Even though it may be possible to set fence posts with mortar, it is often better to use other methods and materials when setting your fence posts.

How to Use Mortar When Setting Fence Posts

Should you decide that you want to use mortar, there are a number of things you should consider before setting your posts:

  • The weight of the fence
  • The wind strength in the area
  • The type of fence post you have
  • How many fence posts you will be using mortar for

Mortar is weaker than concrete, so if your fence is going to be a heavy fence, there are high winds, or you are using steel or heavy wooden posts, the mortar will not be strong enough to hold the entire fence for an extended amount of time.

However, if you are just resetting a single fence post, and have a bag of mortar lying around gathering dust, you could definitely make use of it.

Likewise, vinyl fences are much lighter than their counterparts of wood and steel. You definitely could use mortar when setting vinyl fence posts.

When setting a fence post with mortar, make sure to add some small stones or gravel into the wet mix. These stones will add some strength to the mixture and provide ample opportunity for the mixture to grab and bind onto the surrounding materials.

You could also lay stones at the bottom and edges of your post hole to provide an extra layer of support.

The Difference Between Mortar And Concrete

Even though there are situations in which using mortar works great, concrete is almost always a superior material to use when setting fence posts. Understanding the difference between mortar and concrete will help us to understand why concrete is superior for this use.

What is Mortar?

Mortar is a binding agent by nature. This means that its purpose is to bind two materials or objects together, such as bricks to other bricks and tiles to the floor.

Dry mix for mortar is made with cement, fine sands, and sometimes lime.

However, mortar’s composition makes it weaker by nature than concrete. Most mortar once set for 28 days has a strength of around 750 PSI (Pounds per square inch).

What is Concrete?

Concrete is an incredibly strong and versatile building material. When the dry mix is added to water, it turns into a semi-liquid state that can be poured into molds and shapes. It then hardens into a rock-like substance in the forms it was poured into.

Similar to mortar, concrete’s dry mixture is made with cement and sand. However, there are additional ingredients that give the concrete its strength: gravel and other coarse materials. Concrete set for about 28 days has an approximate strength of 4,000 PSI.

Even if you find cracks in your concrete, there are many concrete patching mixes you can find that will quite permanently fix the cracks.

Concrete is what we would recommend using when setting your fence posts. Using concrete will ensure that your fence will remain strong for years.

MaterialConcreteMortar
PurposeStructure, strengthBinding materials together
CompositionCement, sand, gravel, coarse aggregateCement, fine sand, lime
Strength (After being set for 28 days)4,000 PSI750 PSI

When Should You Not Use Concrete?

So far, we’ve examined why concrete works better for setting fence posts. However, there may be times where neither concrete nor mortar is a good solution.

For some types of fence posts, setting them in the ground with concrete or mortar could possibly make your life harder rather than easier.

Wooden Fence Posts

One of the main problems with wooden fence posts is their tendency to rot and their lack of weatherproofing. Concrete and mortar have a habit of increasing the problem.

When temperatures fluctuate, like in-between seasons, the concrete and wood expand and contract. Because of this, a slight gap forms between the post and the concrete.

This gap is your worst enemy!

Rainwater and water from your sprinklers will pool into the gap and sit there with no where to go, rotting away at your beautiful wooden posts.

Then, when you want to change out your rotten fence post for a fresh one, you have to break away at the concrete.

If you want to use concrete as an anchor for your wooden fence posts, having the concrete anchors be above ground is a great option. Otherwise, you can use a mix of stones, gravel, and soil to set your posts to avoid the gathering of water around the fence posts.

Steel Fence Posts

Steel and concrete go together almost as well as bread and butter.

Steel is used to reinforce concrete when using it as a building material. So, setting your steel fence posts with concrete makes complete sense and works like a charm. In fact, there is little sense in using much of anything else when setting your steel posts.

Vinyl Fence Posts

Vinyl is not in danger of rotting like wood posts are, so vinyl works great with concrete. Concrete works very well to stabilize an otherwise flimsy vinyl fence.

Pretty much the only thing to watch out for when setting vinyl fence posts in concrete is that over time, the fence may begin to wobble just slightly. This is due to the concrete expanding and contracting with temperature fluctuations and causing a slight amount of space between the concrete and vinyl.

The fix for this is to use some concrete patch mix and spread it in the space in between the post and the concrete.

Mortar can be used, but make sure you know what you are getting yourself into before hand.

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