Photo: Julia Larson

Is post foam as strong as concrete?

Concrete is more durable and can support load-bearing posts. Expanding foam works best for lightweight vinyl or mesh fences. Concrete takes longer to set and cure. Expanding foam is more expensive than concrete.

angi.com - Expanding Foam vs Concrete Posts: Pros and Cons

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Highlights Expanding foam and concrete are promising options for post hole fillers.

Concrete is more durable and can support load-bearing posts.

Expanding foam works best for lightweight vinyl or mesh fences.

Concrete takes longer to set and cure.

Expanding foam is more expensive than concrete.

Get quotes from up to 3 pros ! Enter a zip below and get matched to top-rated pros near you. Find pros There’s no point in investing in a fence if it will lean or fall over within a few years. The key to a fence that withstands high winds, climbing kids, and dogs is a durable, strong material to set fence posts. Concrete is a popular filler choice, but you should also consider another concrete substitute for posts: expanding foam. We’ve examined both materials to help explain the difference between expanding foam vs. concrete for fence posts and make your decision easier.

Pros and Cons of Filling Posts With Expanding Foam

Expanding foam, or polyurethane foam, was invented in the 1930s for the military and aviation industries, but it also serves as a material for insulation and setting fence posts.

Pros

Expanding foam is generally considered more eco-friendly than concrete because it produces less waste. It also sets and cures quickly (in less than 15 minutes) and can be applied in cold temperatures. Expanding foam is also lightweight and a smart choice for a DIY since it doesn’t require mixing.

Cons

Fast curing times may seem like an added perk, but this means you’ll have to work fast to get it right the first time. There’s little room for adjustments once you start applying this material. Expanding foam is more expensive than concrete but also less durable. Related Article A Guide to Choosing the Best Wood for Fence Posts The key to a long-lasting fence is choosing the best wood

Pros and Cons of Using Concrete for Fence Posts

Most homeowners default to concrete as a post hole filler for a good reason: It’s durable and reliable. If you mix the concrete properly, this material can last 50 years or more.

Pros

Concrete is less expensive than expanding foam and is best used for load-bearing posts (even deck posts). It’s also more sturdy once set, so you’re less likely to deal with a leaning or sinking fence down the line. Mixing concrete is a pretty simple DIY, as long as you follow the mixing instructions. But if you make a mistake, concrete is more forgiving since it doesn’t dry as quickly, so you’ll have more time to adjust the fence posts.

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Cons

Concrete can take up to a couple of days to fully cure, so you may need to put in some temporary supports to hold the fence posts in place. If installing the concrete post filler yourself, remember that this material is heavy to tote around the yard. Related Article Pros and Cons of Wood, Vinyl, Composite, and Aluminum Fencing No more straddling the fence; find out how these fencing materials compare when placed head-to-head

Expanding Foam vs. Concrete Fence Post Hole Filler

A well-built fence is only as good as the supports it rests on. When it comes time to choose a setting material, you’ll need to weigh your options for durability, cost, and ease of installation.

Durability

Expanding foam offers more support for a simple fence post because it expands to fill every crack and crevice in the post hole. That said, it’s not meant to hold a lot of weight. Concrete is the most durable and can support load-bearing posts, such as posts for decks or fence gates, but it is prone to cracking over time. When installing fence posts with concrete, it’s important to mix the concrete properly to help it last for 50 or more years. Expanded foam lasts from 15 to 40 years as a post hole filler. Both materials offer support, but concrete will likelyto last longer with proper installation.

Most durable: Concrete

Price

Although expanding foam is significantly more lightweight than concrete, it is also more expensive. Expanding foam will cost about 25% more to three times more than concrete for filling fence post holes. The cost of concrete for post bases is about $8 to $10 per 80-pound bag, and you’ll need one to four bags per post.

Best price: Concrete

Ease of Installation

Concrete has some installation benefits—namely that it takes at least 30 minutes before it starts to set. That means you have some time to adjust the post until it is just right. In contrast, expanding foam starts to set almost immediately, so you need to move fast and ensure you place the post properly before applying it. Expanding foam is also easier to handle than concrete during installation. For small holes, you can purchase sprayable foam that requires no mixing. Expanding foam also comes in a lightweight bag ready to mix. A 2 ½-pound of expanding foam mix will fill the same number of post holes as 100 pounds of concrete mix.

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Easiest to install: Expanding foam

Uses

You can use concrete or expanding foam for many different types of fences . Some use expanding foam as insulation or to fill any holes or gaps around the house, in addition to a post hole filler. While expanding foam can secure posts for lightweight fences such as vinyl or wire mesh, it’s better to go with concrete for structural posts, such as posts for porches, decks, or large and heavy gates. Expanding foam is not as strong as concrete when supporting load-bearing posts. A local fence installation professional can help you decide which post hole filler is best depending on the type of fence and uses you need.

Most versatile: Concrete

Ease of Repair

Both materials, once set, are pretty tough to remove should you need to repair or replace sections of your fence. That said, concrete will support common fence post repair materials, like brackets or spikes, but expanding foam will not. This is because the added weight of the repair devices may crush and weaken the foam and the entire foam post support system. If you ever need to replace a rotted fence post (or porch or deck post), you’d need to dig up the entire post/filler unit and then remix and reset with a new post.

Easiest to repair: Concrete

Sustainability

Considering how long it lasts, concrete may seem more sustainable than expanding foam, which is a type of plastic. But expanding foam requires less energy and materials to manufacture than concrete. It also produces less waste during the filling process, making expanding foam a more sustainable option.