How to pour a concrete floor for an existing garage Best How-To Guide

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Phil Puccio

how to pour a concrete floor for an existing garagePouring a concrete floor in an existing garage

This is my guide for Pouring a concrete floor in an existing garage, House or shed foundation.

The term “concrete floor” is used to describe when you are pouring concrete into an existing building, into a concrete foundation, or into ICF styrofoam block walls.

A “concrete slab” is when you use 2×6 or 2×12 molds and build a frame to pour the concrete into the molds. To learn how to shape and pour a concrete slab, Click here.


  1. Prepare the lower level
  2. Install vapor barrier and reinforcement
  3. Call to order your ready-mix concrete
  4. Place, screed and bull float smooth the concrete floor
  5. Get the tools you need

Step 1. Pour the concrete floor – prepare the substrate

compact the gravel before pouring a concrete floorLevel and compact the substrate

Install gravel, road surface, or crushed stone in your garage for sub-construction. If you live in a cold climate, you don’t want extensive soils such as loam for subsoil.

The depth of your gravel will depend on your situation, but expect to add at least 8-12 inches of gravel and up to 2 feet if you live in a climate that is several days below freezing in winter.

Rake the gravel level and several times with a. condense Vibratory compactor. If your gravel is very dry, pouring it as it compacts will help.

Step 2. Install a vapor barrier and rebar

how to pour a concrete floorInstall a poly vapor barrier and wire mesh

To install 6 mil plastic vapor barrier on top of the gravel. A vapor barrier prevents moisture from rising through the concrete floor from the subsurface.

If you ever decide to paint or epoxidize your concrete floor, you’ll be glad you did!

Overlap all of the edges at least 6 “-12” and you can seal them with that Vapor barrier tape.

After you are done with the vapor barrier, place a wire mesh to reinforce the concrete. Most woodworking companies stock wire mesh for concrete like the wire we use. Home Depot and Lowe have it in stock too.

It is best to use some sort of “plate pad” like the one we use to put it under the wire and hold it in the center of the concrete.

When the concrete cracks there is a wire mesh to hold the concrete together. It will help prevent the crack from spreading, lifting, or getting bigger.

Wire does not add strength to the concrete or keep it from cracking. You need to saw shrink joints in your floor to avoid cracking.

Step 3. Call and pre-order your precast concrete

how to pour a garage floorOrder your concrete in advance

You should call and pre-order your ready-mix concrete at least a week before pouring your concrete floor.

Most ready-mix concrete companies are very busy and have projects planned days in advance.

If you ask the concrete dispatcher, they can calculate how many cubic feet of concrete you will need based on the dimensions and thickness of your floor.

You can also use this specific calculator to figure out how many meters you need.

Most of the concrete floors I install use a 3000 psi mix with 3/4 “aggregate. This is a good, strong mix for a garage floor.

Step 4. Laying (pouring) the concrete floor

how to pour a concrete floor in an existing garageUse the concrete cart slides to lay the concrete in the ground

When the concrete arrives at the job site, tell the truck driver to mix the concrete to a 5 “or 6” slump.

Slump is how loose or dry the concrete is when it comes out of the truck. A 6 inch break-in is a good workable break-in when pouring a garage floor.

The concrete cart has chutes that go about 20 feet to place the concrete. It’s usually pretty easy to pull the concrete another 4 or 5 feet further with a concrete rake.

If you need to lay concrete further than about 7 meters, other means will be required. I use a 12 ‘or 16’ aluminum slide to get further. (You cannot find these in tool rental shops). You can also use wheelbarrows to push the concrete (that’s a lot slower, but it works).

Pull and rake the concrete to fill the area. After you’ve poured out a 1/4 to 1/2 of the garage, you can just paint it. (See the video below to learn how to screed like us.)

I use a laser level to mark my floor grades around the outside perimeter, then I snap a chalk line with these marks on the wall.

For the middle grades I use the laser level and make a “wet pad” in the concrete (like in the picture). Then I use the wet pad to scrape the screed and level the floor.

how to screed a concrete floorScreed the concrete with a 2×4 or a magnesium screed

You can use a straight 2×4 screed or a magnesium screed like us. (also rent)

Hit the concrete with your pre-marked degrees on the perimeter and the grading block that you set in the middle.

Once you have finished screeding the concrete, it is time to smooth the surface with a Bull Float and prepare it for finishing.

See how we do pour a concrete floor into an existing garage.

How to swim a concrete floorAfter the screed, smooth the concrete with a bull float

Step 5. Tools you will need to pour a concrete floor

There are some tools that make pouring a concrete floor a lot easier.

Below is a list of tools I use to pour all of my garage floors.

  • Likes swimmers – With this I will smooth the edges up to the chalk line and make my wet pads in the center of the bottom.
  • Laser plane – Use this to set and mark your grades before and during the pouring.
  • Concrete rake – for pulling and pushing the concrete.
  • Screed – is used to “knock off” the concrete and to level the concrete with your soil quality over a large area.
  • Bull hover – for smoothing the concrete after the screed.
  • Concrete extension slide (optional) – helps reach areas that extend further than the truck chutes can reach.
  • shovel – to clean the chutes and remove excess concrete from the cast if necessary.
  • Concrete rubber boots – to carry in concrete and protect your feet & legs.
  • Safety gloves – to protect your hands from concrete.
  • Safety glasses – to protect your eyes.

All of these tools are available on Amazon if you have no way of getting them. The links above are affiliate links and I earn a small commission if you use them to purchase tools within 24 hours of clicking them.

Need help learning to pour a concrete floor?

I have a Video course That will teach you how to shape and pour a concrete slab.

In the course I will show and teach you how to pour a concrete floor.

It will show you how to place and rake the concrete to spread it, how to screed, bull float, mag float the edges, all you need to know.

Can I pour concrete directly on dirt?

Yes, you can pour a concrete floor directly onto dirt. If your dirt base is “dry” with no moisture problems, it is okay to pour concrete directly on top of the dirt.

It is a good idea to install floor drainage when installing the gravel sub-base. The drainage pipes help to drain away the water that seeps under the plate in the future.

If you are concerned that moisture vapor could rise through the concrete floor and potentially damage your flooring or epoxy coating, pouring concrete directly on top of the dirt is not recommended.

Use a 6, 10, or 15 mil poly vapor barrier under the floor if moisture could cause problems later.

How deep does a concrete floor have to be?

The average thickness of a residential concrete floor is 4 inches deep. Four inches of 3000 psi concrete mix placed on a well-compacted gravel floor is strong enough to support cars and pickups.

If you are using the concrete floor for heavier equipment or utility vehicles, consider a 4000 psi concrete mix and a 6 “or 8” thick concrete floor.

Learn more about concrete mix designs here.

do it yourself pouring concrete

If you want to pour a concrete floor and do it yourself, check this out Concrete slab beginners video to get a good idea of ​​how a slab is cast.

And for more help, go to how to pour a concrete floor in a crawl space.

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