Much like the footing of a house, a well-constructed fence starts with a secure foundation. Setting your fence posts in concrete will ensure they stay put no matter what the conditions– and will remain upright for years to come.
There are few things as satisfying as putting up your own fence. While it may seem a little intimidating at first, setting fence posts in concrete is the way to go when you want a professional-grade job.
If the idea of mixing batch after batch of concrete sounds tedious to you – you’ll be happy to know there are several no-mix concrete products designed specifically for this task! This allows you to pour the dry concrete mix directly into the post hole, and then add the water in afterward.
I’ll break down everything you need to know about how to set a fence post in concrete – so you’ll be able to put up your own fence at a fraction of the cost of hiring a contractor.
Tools & Materials Needed
- 4 x 4 pressure treated posts
- All-purpose gravel
- Quickrete fast-setting concrete mix
- Dust mask, eye protection & waterproof gloves
- Posthole digger or auger
- Tape measure
- Garden spade
- 5-gallon bucket
- Post level
- String and stakes (for marking post placement)
Setting Fence Posts in Concrete – Step-by-Step Guide
Step 1: Measure and Mark Postholes
Before you can start digging up your yard, you’ve got to determine the placement of your postholes.
Many fence panels measure 8 feet long, so you’ll want to measure and mark the location of your holes every 8 feet with a small stake, spray paint, or some other easy-to-spot method.
Before you break ground, it’s a good idea to make sure you won’t be digging into any underground utility lines. Contact your local municipality if you’re not sure about the location of these lines.
Step 2: Dig your Post Holes
There are a number of different methods you can use to dig your fence post holes.
Keep in mind the more postholes you need to dig, the more effort will be required, so renting a powered auger makes sense if you’ve got a lot of holes to dig. These bad boys will dig through tough compacted soil like a knife through butter!
If you’ve only got a few postholes to dig, then a clamshell-style posthole digger can work well. You can also use a shovel in conjunction with a heavyweight tamper/posthole digger bar to make a few holes.
In my case, I only had two postholes to dig, so I opted for the old spade shovel and heavyweight digger bar method. This method works very well if you’ve got tough clay-rich soil that’s too hard to dig with a clamshell-style digger. The bar weighs about 16 pounds, so you can lift it up and use its weight to break through tough clay with great effectiveness.
As a rule of thumb, you want your post hole depth to be at least 1/3 of the overall post length. So if you’ve got 8-foot long posts, your hole should be at least 32” deep. Then add 6” inches to that depth for adding gravel at the base.
As for posthole width, the general rule is for the hole to be 3 times the width of the post. So, a 4 x 4 fence post should have a 12” diameter hole.
Step 3: Add Gravel to the Posthole Base
This isn’t strictly necessary, but adding about 6” of gravel to the bottom of each posthole will help drain away moisture and keep your posts from rotting prematurely.
If you live in a wet, rainy environment or an area with slow draining soil – gravel is a must for keeping your fence post from sitting in water.
After you add the gravel, use a tamping bar, a spare piece of lumber, or the bottom of the post hole to tamp it completely flat.
Step 4: Position the Posts inside Postholes
This part can be a little fiddly, but there are few simple tricks you can use to ensure your posts are positioned exactly where they need to be. If you have multiple posts to set, then setting up a string line will ensure their all perfectly aligned with each other.
To make a string line:
- Setup the two end posts on each side of your fence. (If you’re replacing an old or damaged fence you can use the existing posts on each side.)
- Drive two small nails into each side of both end posts about 6 inches from the bottom and 6 inches from the top.
- Tie a length of string tightly between the nails and secure it with a knot.
- Now you have a guide showing you exactly where to position your posts.
Set the post inside the posthole and hold it in position. You can have an assistant help you with this step, or use some spare lumber to hold the post in place. Use your level to make sure the posts are plumb and level before you start pouring the dry concrete mix.
Step 5: Pour the Dry Concrete Mix
Now it’s time to pour the dry concrete mix into the posthole. Using some form of a dust mask and eye protection is a good idea, as the concrete mix will create dust as you pour, and you want to avoid breathing in the concrete mix as it can lead to serious problems.
If you’re not sure how much dry concrete mix you’ll need, Quickrete has a handy calculator that will give you a good estimate. In my experience, it tends to overestimate a little, but it’s better to have a little extra than not enough.
Pour the mix slowly and evenly until you’re about 3 to 4 inches from ground level.
Step 6: Add Water to Dry Concrete Mix
Next, add the recommended amount of water to the dry concrete mix. You may need to add the water in increments, as it takes a while to soak through.
After you’ve added the water, it’s a good time to double-check that your posts are level and plumb. When the concrete is wet you can still move the post a little, but you won’t be able to do so for long.
The Quikrete takes about 20 to 40 minutes to set according to the manufacturer, although this can vary depending on the temperature as well as the soil dampness. It should be dry enough to work with after 4 hours, although letting the concrete cure for 24 to 48 hours before adding fence panels is a surefire way to get a solid footing.
Step 7: Fill in Top of Posthole
After your fence post has set in the concrete (about 4 hours) you’ll want to fill in the last 3 to 4 inches of space in the posthole.
You can use some of the soil you dug up previously to top off the hole, or you can use another batch of concrete to create a sloping top that will cause moisture to flow away from the fence post.
To create a sloping concrete top:
- Mix a smaller batch of concrete using the leftover mix you have from before.
- Fill the top of the hole with mixed concrete.
- Use a trowel to create a slight angle from the base of the post down to the edge of the posthole.
Step 8 (Optional): Seal the Post with Caulking
Although a fence post set in concrete is extremely strong and durable, it has one major downside. It’s vulnerable to rotting if moisture is able to pool around the base of the post. This can happen when small cracks naturally develop between the concrete and the post over time.
One way of guarding against this is by applying a heavy-duty outdoor caulk right where the post meets the concrete. Use a caulking gun with an exterior silicone or acrylic latex caulk that will bond with concrete.
Hopefully, you now have a good idea of how to set a fence post in concrete. While it can look intimidating, once you get into the swing of things, you’ll wonder why you haven’t been doing this your whole life.
If you have broken fence posts that need removal before installing new ones, check out my post here.