Expanding Foam vs. Concrete: Which is the Best Option for Securing Your Fence?

Written By Kenneth Wilson  |  0 Comments

We know — setting a fence post can seem intimidating. But trust us, finding the best setting option for you is not as confusing as it may seem. Whether you are building a brand new fence or updating and repairing an existing one, one of the most important decisions to make is how to anchor the posts into the ground for stability and longevity.

Depending on the type of soil, the time you have available and, of course, your budget, you have a few different options. Today, we’re going to walk you through two good options so you can figure out what is right for your project.

1. Traditional Concrete

The first, most common and time-tested option is concrete. Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement that hardens over time. Concrete has been used for years to stabilize and (enhance) the longevity of fencing. It is heavy duty and no nonsense. It’s easy to come by and cost effective for big jobs.

Why use concrete?

Concrete is a good option for its strength and viability — concrete tends to have a long lifespan, cutting down future time you might spend resetting your fence post in the future. If your main concern is security, concrete is a no brainer.

Steps to set your fence post with concrete:

  • Dig a hole for your post.
  • Mix your bag of concrete. Follow the instructions on the bag, mixing the appropriate amount of water with the mix until it is fully blended.
  • Put the post into the hole. 
  • Pour your concrete into the hole. Once you fill your hole with concrete to secure your fence post, expect around a 20-40 minute wait time before it sets.
  • Use braces to balance the post in place for 5-10 minutes.
  • Remove the balancing brace and allow at least 4 hours (ideally closer to 24-48 hours) of dry time before putting the rest of the fence up.

Pro tip: you’ll want  to dig a 2 feet hole into the ground so that the post can sit 2 feet deep before you secure it with the concrete.

By setting the post 2 feet deep, your post will be reinforced by concrete even beneath the surface and be able to withstand high winds.

2. Expanding Foam

Option two, gaining more popularity each year, is expanding foam. Expanding foam expands and hardens. Most often found in a canister with a spray nozzle, expanding foam is easy to apply in a variety of situations. It generally comes in a two part mixing bag, requires no water and is mostly mess-free.

Why use expanding foam?

Expanding foam is a mostly self-contained system of two bags separated by a seam that when you are completely ready to pour and set the post you burst one of the bags into the other and it combines, while still contained in the bag. You will have to be prepared to act quickly and not get distracted as, after only 15-30 seconds (depending on the brand), it will be ready to pour and begin to rapidly expand and set within 3-5 minutes. You will have this 3-5 minute window.

Though expanding foam is most commonly used as a form of insulation, it can also be used to secure fence posts; it will rapidly increase to 15 times its size to fill around and into all crevices around the post. It is ideal for fencing as it is a light load bearing product, and it boasts being extremely durable and highly resistant to the infiltration of moisture (which could destroy your fence in cold climates).

Steps to set your fence post with expanding foam:

  • Stick your post in the hole. Similar to concrete, you’ll want to set the post a few feet into the ground before you begin to secure it in order to protect from wear-and-tear and high winds.
  • Mix your expanding foam. Expanding foam is a two-part polymer that is mixed before being poured into the hole around the post. Be quick with pouring - you have only 20 - 30 seconds before the product begins to dry.
  • Evenly pour the expanding foam into the hole. Since expanding foam sets fully in just three minutes, it’s important to spread this quickly but precisely.
  • Apply light pressure to the fence post and keep it in place for between 3 and 5 minutes. Similar to concrete, you can use balance braces if you think it’s necessary.
  • Let the post set for the next  5-10 minutes, ensuring that it stays completely level and does not shift.
  • Remove the balancing brace and check to see if it is secure.

Concrete vs. Expanding Foam: Pros and Cons



  • Cost. A bag of concrete, on average, is about half the price of a bag of post foam. 
  • Time-tested. Concrete has proven time and time again that it is the most long-lasting and secure for post anchoring.
  • Heavier. Concrete’s heavier weight makes it better for anchoring a larger load bearing post.


  • Slower Curing Time. Concrete ideally takes 24–48 hours to cure completely, making your goal of securing your fence post a more than one-day job.
  • Can be easily cracked by water. Concrete can be penetrated by  water, which can lead to deterioration or breaking down of the concrete itself, making it less safe for long term use in cold or wet climates. 
  • Bigger Post Hole. When using concrete, a hole for a 4” x 4” (10 x 10 cm) post has to have a diameter of at least 8” (20 cm). This is because concrete is very thick and cannot be placed in a smaller hole. There would be large air pockets in smaller holes, which would make the concrete very weak.

Expanding Foam


  • Lighter. Bags of post foam are going to be much lighter and easier to handle and use than bags of concrete.
  • Faster Curing TimeExpanding post foam is going to mix and start expanding within 1530 seconds (depending on brand) and fully harden within 1530 minutes. Cutting your project time down by 24 hours or more.
  • Waterresistant. Post foam is water-resistant when fully cured. It will help prevent water from penetrating the post, decreasing the chances of rot, decay and deterioration.


  • Price. More expensive than the traditional concrete options (around 2x more expensive).
  • Load Bearing LimitsExpanding post foam is not intended for large load bearing projects.  
  • Repairs Can Be DifficultRepair methods used with concrete cannot usually be used with post foam. A common example is a fence post repair bracket being used between the post and the concrete to repair the stability of the post. This method can crush the post foam and render it useless and needing to be fully replaced.

Final Thoughts

Though concrete is a great option, we recommend the new kid on the block: expanding foam. Expanding foam is easier to work with, quicker, and creates an equally solid foundation for the  post (and ultimately the fence). As expanding foam expands in all directions, it allows the foam to adhere to anything in the hole, and ensure every crack is filled to security.

So while concrete of expanding foam will do the trick, the pros of expanding foam lead us to believe it to be the superior option, especially for those not wanting to  put in the extra elbow-grease concrete provides! 

About the Author

I can build it, and I can help you get the patio enclosure you want! I got my start in the Florida patio industry back in the 70s as a young general laborer looking for something to make a few bucks. At the time I never thought it would end up as my career. Over the years I grew beyond the laborer position, becoming a foreman, superintendent, and then into executive management for some of the largest patio contractors, and material vendors. Now into retirement and slightly bored, I offer consulting services to new and existing contractors, and publish this website to help the people who love their patio's and screen enclosures the most - YOU!

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