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How to Pour a Concrete Slab

Estimated Reading Time: 12 min

A fresh concrete slab is a great way to enhance any outdoor living space – and it’s easier (and more fun) to achieve than you think.

9/29/2021

Cost
Skill Level
Intermediate
Approximate Time 2-4 hours
plus 24-48 hours cure time

Concrete is one of the most economical, durable, and versatile materials on the market. It’s easy to use for DIY walkways, patios, or foundation slabs for a garden shed regardless of your skill level, making it a great cost-effective and fun choice for many DIYers looking to deck out their outdoor space. Pouring a slab yourself can easily save you half of what it would cost to hire it out, plus it’s pretty fun to pop on a pair of rubber boots and stomp around in wet cement as you pour, push, and pull it into place. All you need to get started is a clear day, a buddy, and the right tools.

Here's what you'll need:

Materials
  • 2'x4's
  • Gravel OR Sand Fill
  • Concrete (Bagged OR Delivered—more on this in Step 5)
  • OPTIONAL MATERIALS
  • Welded Wire Mesh OR
  • Rebar
  • Double Looped Ties
  • Wire Twister
  • Rebar Chairs
Tools
  • Hammer and Nails OR Drill and Screws
  • Level
  • Tape Measure
  • Pencil
  • Shovel
  • Tamper
  • Wheelbarrow
  • Concrete Placer
  • Screed
  • Magnesium Float
  • Edger
  • Concrete Broom
  • Groover (for slabs over 10 ft.)
For Your Safety
  • Rubber Boots
  • Rubber Gloves

Step 1

Prep Work

Doing prep work before you get to pour any concrete may seem tedious but skipping over these crucial steps could result in unlevel, oddly shaped slabs prone to shifting and cracking. Here’s what you’ll need to do before you pour any concrete:

1.     Find a Spot and Make a Frame

First, grab a few 2 x 4’s and use the lumber to measure out and frame the area to your desired slab size (whatever best fits your space and needs). Cut your frame to size and use nails or screws to secure your frame together.

2.     Make Sure Your Frame is Square

You can make sure your frame, and therefore your slab, is square by using the Pythagorean theorem (you know, the one you told your math teachers you’d never use).

Here’s a quick refresher: a2 (Side #1) + b2 (Side #2) = c2 (hypotenuse).

Keep it simple by using round numbers, like this:

32 + 42 = 52.

Measure frame using 3, 4, 5 method to ensure its square

In other words, when you measure 3 ft along Side #1, then 4 ft along Side #2, the hypotenuse (or the distance between them) should measure 5 ft. If it does, your frame is square; if not, it’s time to adjust.

3.     Get Ready to Dig

Before you do any digging, you should always call 811 or visit call811.com to get a fix on the location of any pipes or wires that may be buried in your yard so you can avoid a costly mistake. This number works anywhere in the country.

Once you’ve been given the clear, you’re ready to start digging.

Step 2

Dig A Space for Your Pour

The goal of digging out a space for your pour is to make the space as level as possible before you begin pouring concrete to help reduce the risk of your slab shifting or cracking over time.

Start by placing your completed frame where you want the finished slab to be and score along the outside edge with the tip of your shovel. This will give you a guiding line to follow when you start digging.

Next remove your form and set it aside to begin removing your sod and the first four to six inches of topsoil. The general rule of thumb is to allow about three inches for the gravel base and four inches for concrete.

Pro Tip

It is perfectly acceptable to start this entire process by digging a space for your pour, then building forms to fit the space. Choose a starting point that works best for you.

You may need to use a hoe (or a grubbing hoe) if your dirt is too tough for your shovel alone. This will rough up the soil to make it easier to remove with your shovel. A second pair of hands speeds up the process.

And here’s a piece of good news—the hole doesn’t have to be perfect right now. Just get it as flat and level as you can.

Step 3

Place Your Frame and Add Sand or Gravel Fill

Once your hole is dug, replace your frame and get it situated exactly where you want it, then secure it in place by hammering stakes around the outside edge of the form (about every two feet). Check periodically to ensure your form is level all the way around. Then, use a hammer and nails to secure the stakes to the form. This will help keep your forms in place during the pour.

Note: These stakes should not extend over the top of your forms. If they do, cut them down to size using the top edge of your forms as a guide, otherwise they’ll get in the way by the time you make it to Step 6.

This process may make your form seem elevated in some places and lower in others (like in the image below), but don’t worry, that’ll be taken care later.

Place concrete form

Now it’s time to add your fill.

 

Q: Should I use sand or gravel fill for my concrete slab?

A: It depends on where your slab is and what it’s being used for. For instance, all-purpose sand fill is most useful in wet areas that need a little extra help with water drainage. It’s easy to move around with your hands and pretty affordable, but there is a catch. Sand is prone to shifting and displacement, which means your new slab might not stand the test of time. Gravel fill is a sturdy enough material that, when tamped down, proves to be both a budget friendly and long-lasting option for many DIY projects.

 

Pour and spread out your fill until you have a relatively even, three- to four-inch bed of material.

If you notice that you have gaps between your fill and the bottom edge of your form, you’ll need to “grade” the fill by adding more gravel or sand to those low areas and spreading them out evenly until they match up with the rest of the fill. An easy way to double-check your work is to place a screed (or, simply, a long straightedge like a 2 x 4) on top of your form and measure down with a tape measure, making sure it measures the same all the way around.

Check gravel fill level

For those who decided to use gravel fill, you’ll need to use a Tamper to form a compact base (sand is naturally compact thanks to its tiny grains, so there’s no need for tamping) by bouncing the tool over the surface until it’s fairly level. A good, compact base will be the crucial difference between a slab that lasts and one that cracks and shifts.

Dampen the gravel or sand using your garden hose and a misting attachment to help prevent shrinkage cracking—this is especially important if you’re working outside on a hot day.

Step 4 (Optional)

Lay Rebar or Welded Wire Mesh

A common question is if rebar is required for every concrete project.

The answer—rebar is strong, durable, and placing it within your concrete slab will make it tougher than nails, but it’s not always necessary for every project.

Rebar is recommended for concrete slabs that measure 5 – 6 inches in depth, which is about the depth of slab you’d need if you plan to drive on it or use it to house heavy machinery (like a large RV, for example). If your slab is under 5-inches deep, or if you plan to use it as a patio, sidewalk, or garden pad, you’ll likely be fine without it.

You could opt in for a welded wire mesh instead of rebar. It’s a thinner, typically cheaper alternative to rebar and offers similar benefits to rebar, including the reduced risk of your slab cracking over time.

Here’s the steps needed to install both options.

1.     How to Lay Rebar for a Concrete Slab

Place rebar in an evenly spaced grid pattern like the example shown below and overlap any pieces to make up for the length needed to span your slab.

Lay Rebar in Grid Pattern

Loop a double-looped tie around every intersection and twist with a Wire Twister to secure the rebar together, then use the toe of your boot to press the tie down flat against the rebar or remove it completely using wire cutters.

Center the rebar where you want it (the ends should be about two- to three-inches away from the edge of your form) and elevate it with Rebar Chairs so the rebar hits in the true center of the slab instead of the bottom. You also don’t have to remove the Chairs as you pour. Leave them in and let them handle the load for you.

2.     How to Lay Welded Wire Mesh for a Concrete Slab

Welded Wire Mesh already comes in a grid pattern, which saves you time and manual labor. Simply lay out the sheets (as many as you need to support your slab) and you’re good to go.

You can use chairs to keep the mesh elevated, but because it’s so lightweight, it's easy to adjust it back to the center of the slab as you pour fresh concrete.

Pro Tip

This mesh is sometimes sold in rolls, but we recommend sticking with the flat stuff—trust me, it’s not easy to flatten out steel once it’s been rolled up for so long, even if it is thin and seemingly malleable.

Step 5

Mix and Pour Concrete

The amount of concrete you’ll need for your project is completely dependent on the dimensions of your slab—particularly its volume (typically measured in cubic yards)—and you can use a concrete calculator to calculate the right amount.

Depending on your budget, you can either call your local concrete provider to have them deliver ready-mix concrete directly to you, or you can visit a home improvement center to get the amount of concrete you need, mixing it yourself in a wheelbarrow or a Concrete Mixer.

If you decide to mix it yourself, follow the directions as written on the bag.

Caution

Wet concrete can be damaging to exposed skin. Always wear the proper protective gear when working with this material.

Now comes the fun part—the pour. Concrete can set pretty quickly in hot temperatures, so once you get going, it’s just go, go, go!

Pouring concrete into forms

It’s important to work in sections when pouring concrete because 1) it’s easier to spread around with a Placer or hoe, and 2) it gives you the chance to be sure your rebar or mesh is still where it needs to be. As you move the concrete, the surface should be relatively flat and slightly higher than the edge of your form (you’ll need this extra material when screeding).

Step 6

Screed the Surface

“Screeding” is an industry term that ultimately boils down to working a straight edge (either a Screed or a 2x4 that matches the width of your pour) in a sawing motion over the top of wet concrete to fill any voids and smooth out the surface.

Always use the top edge of your form as a guide for your screed, and don’t let the screed dig deep into the wet concrete. Think of it as skimming over the surface to smooth out the bumps.

screed concrete surface smooth and level

For larger slabs (anything longer than five-feet), you can screed as you go (like the example above) to streamline the process. Those of you making smaller slabs can screed once the entire form is filled. You’ll need about three to four passes with the screed to see the best results.

Scoop up and clean away any concrete that may have bubbled over the side of your forms and onto the grass. If it hardens, it can make removing the forms much more difficult.

Step 7

Trowel, Edge, Groove, and Broom Your Slab

Wait until the concrete has lost a bit of its sheen before using a Magnesium Float to remove any marks or blemishes that may have been left behind after screeding. About two to three long sweeping passes should do it.

Next, round out the edges of the slab using an Edger (the concrete should be firm, but not solid, before you begin edging). Work in long, sweeping strokes until the edge is smooth, solid, and straight. You may need to go back over the surface with your trowel if the edger leaves behind any lines.

If your pour is longer than 10 ft., you’ll need to cut in a control joint (better known as a groove) to prevent cracking. So, while the concrete is still wet, find the center of your pour and mark the spot on the form with a pencil, stretch mason’s line over the surface to create a guiding line in the concrete, and follow the line with a Groover to create a perfectly straight and centered control joint.

Pro Tip

For larger slabs, use a Bull Float and fit it with a handle to extend your reach, allowing you to push and pull the tool over the surface of the slab to remove screeding, edging, and groover marks. Two to three passes with this tool should be enough to smooth out the surface without weakening it.

Finally, finish the slab with a Concrete Broom to create a non-slip surface with enough traction for foot traffic without being rough enough to hurt if walking on bare feet. Simply glide the broom over the surface, pulling toward you so all the grains face the same direction, and repeating this process until the whole slab is covered.

Step 8

Finish it Off!

Leave the slab to cure completely (this could take one to three days), then remove the stakes and the frame. You may need to loosen the boards with a hammer or pry bar, but they should easily pry free.

Once they're off, clean up the debris, give the slab one final sweep, then adorn it as you see fit for years to come.

 

Don’t want to waste time finding the right tools for the job? Click the button below to add everything you need for a successful pour directly to your shopping cart.

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