Some jobs start with a hammer. But this one starts with a shovel and some common sense.
Pouring a concrete slab in your pole barn isn’t something you slap together in an afternoon. Do it right, and it’ll serve you well for decades. Do it wrong, and you’ll be cussing that cracked, wavy mess every time you walk across it.
Let’s walk through the steps to pour a clean, level slab inside your new garage, warehouse, horse barn, or whatever post-frame structure you’re building.
1. Grade First, Build Second
Before a single post goes up or a hole gets dug, your site needs to be prepped.
Start by stripping off any topsoil, sod, or organic material. That’s not the stuff you want under your barn—it breaks down and shifts. Then rough grade the pad with a skid steer or tractor. Your goal is a solid, level surface, typically raised above surrounding grade for drainage. Fill low spots with clean fill or gravel and compact everything tight.
Use a plate compactor, not just your truck tires. If your boot leaves an imprint, it’s not ready.
A Handy Tip: A good slab starts with a solid base. You don’t build your life on sand, and you sure don’t build your barn on soft dirt.
2. Frame the Building Before the Pour
Once your pad’s solid and level, you’re ready to build. And here’s a rule I won’t budge on: Don’t pour your slab until the barn is framed and the roof is on.
Leave the wall panels off—that’s fine—but the posts, trusses, skirt boards, and bracing all need to be installed. That way your pour is protected from weather, and your building is locked in and square. It also gives you built-in edge forms thanks to those treated skirt boards.
If you’re pouring before the roof’s on, you’re gambling with rain, sun, or a change in alignment. That’s a bad bet.
3. Gravel and Vapor Barrier Go Down
With the frame up and the site ready, it’s time to lay your gravel base.
Spread 4–6 inches of clean, crushed stone—¾” limestone or #57 is great. Avoid rounded or unwashed gravel. Compact it in lifts to keep things tight. This provides drainage and a stable sub-base for the slab.
Right after your gravel base is compacted and flat, it’s time to lay down your vapor barrier.
This thin sheet of plastic may not look like much—but it’s a critical layer that protects your slab from moisture creeping up from below.
Use at least 6-mil polyethylene sheeting, but 10-mil is better. It’s thicker, more puncture-resistant, and stands up to walking, rebar chairs, and rough gravel.
Overlap all seams by at least 6 inches.
Run the vapor barrier up to the skirt boards or temporary forms, and don’t leave gaps around the edges.
A Handy Tip: Go with 10-mil plastic. It holds up better during the pour—less likely to tear under boots, tools, or mesh chairs. You only get one shot to do it right, and that extra thickness helps keep moisture where it belongs.
4. Use Skirt Boards as Built-In Forms
Here’s one of the best things about a post-frame barn: your treated skirt boards act as the perimeter form for the concrete slab.
But—and this is important—you’ve got to do it right:
Make sure your skirt boards are firmly attached and level during framing.
Pin them between posts by driving stakes or rebar every 2 to 3 feet between each set of posts (usually 8′ apart).
This keeps them from bowing outward under the pressure of wet concrete.
Once the concrete sets, you can’t push those boards back. If they bowed during the pour, your walls will be out of whack forever—and it’ll show.
You’ll also need to add temporary form boards anywhere the slab doesn’t have a skirt board—like across large door openings, apron edges, or open-sided lean-tos. These should be braced well and easy to remove once the concrete cures.
A Handy Tip: Don’t wait to find out your wall is off plumb because your skirt board bulged during the pour. Take five extra minutes and pin it tight.
5. Reinforce the Slab
Concrete cracks. What matters is controlling where it cracks and how bad it gets.
Here’s how:
- Wire mesh: Welded wire mesh (WWM) is rolled out and lifted slightly to sit in the middle of the pour.
- Fiber mix: Order concrete with fiber reinforcement to reduce shrinkage cracking.
- Rebar: Optional, but good near large doors or heavy-use areas.
Don’t skip this step if you want a floor that holds up to years of traffic, tools, and maybe even the weight of your pickup or tractor.
6. Plan for the Pour
Now for the mix. You’ll want:
- 3,000–3,500 PSI concrete for barn slabs.
- Air entrainment if you’re in a freeze-thaw climate.
- Low to medium slump (around 4″) to reduce water content and shrinkage.
- Retarders or water reducers depending on weather and delivery time.
Most pole barn slabs are poured at 4 inches thick, but you can go 5–6 inches in heavy-use areas. Don’t try to “stretch” a load of concrete by pouring it thinner—your boots might crack it just walking across.
If sloping the floor toward a door, only do that in the final few feet near the opening. You don’t want your whole 100-foot barn slanted unless it’s built for drainage.
7. Let It Cure Properly
Once poured and finished:
- Keep the surface moist (cover with plastic or mist it) for at least 3–7 days.
- Avoid driving or storing equipment on it for a week minimum—longer in cold weather.
- Don’t forget to remove any temporary forms once the concrete has hardened.
And finally, stand back and admire what you’ve built. That slab is the foundation of every project, tool bench, tractor, and memory to come.
Final Words
If there’s one thing I’ve learned: a good slab is more than just concrete. It’s preparation. Timing. Patience. And doing the little things right—like pinning skirt boards and laying vapor barriers.
You’ve already built a barn. Now pour the kind of floor it deserves.
Happy pouring
—Albert Barnwright
Design Your New Pole Barn Today – Get an Instant Quote Online!
Call our knowledgeable staff at 800-622-4242. If you’re ready to build your pole building, lock in a quote with DIY Pole Barns using our Instant Quote tool!
Connect with us on social media!