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Concrete/Flatwork/refilling hole in concrete floor

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Question
Hello John,
I'm glad to learn of your volunteering here as I also volunteer in the category of auto repairs.
I live in a 55 year-old California 'modern' home with concrete floor and radiant heat piping distribution therein. I had to dig several holes through the slab entirely to reach and repair leaks in those pipes. So basically I'm at the level of the dirt under the floor with holes of about 1 square foot in area #but not square in shape of course#.
Could you give me an idea of how much of the dirt/rocks  
to put back in the holes, i.e. to build up to how many inches below the level of the surface of the floor? I think the original slab was about 4" thick so I assume I should bring the dirt/rock to that level also if that is correct.
Then I have a bag of concrete mix that I would mix with water and put in the hole and wonder if there are any specific 'tricks'/techniques I should use to do it right. For example would I fill the holes in a single pass or do it in 2 steps of about 2" thickness each to allow for settling of the bottom layer before finishing it to the surface? Other than trowel/large spoon and flat plate to smooth it should I have other tools ahead of time? I am borrowing a mixing tray from a friend. How much time do I have to put in the mix before it sets up too much to work with?
Thanks so much for any direction you can give me. I haven't worked with concrete before this situation.

Answer
Roland,

Sorry for the delay, I have been working 7 days a week and sick for the last month!

It sounds like you are well on your way with this.  I would fill the dirt back in and replace it with the same thickness of concrete as you had before (4")  That being said you may want to consider what kind of traffic and floor coverings you have and will that "patch" become an issue later.

I am assuming just foot traffic in your home, so this isn't as important as if you were driving a car over it in your garage.

The "jagged" nature of your holes will likely be an advantage in this situation.  You most concrete repair products don't really stick well to other/existing/cured concrete.  You won't want this patch to be able to move up or down over the years.

I would fill, mix your concrete, and trowel it by hand with the tools you are going to borrow from your friend.  Mix per the instructions on the bag, and you should be fine  There is often a tendency to put too much water in the mix, which may cause you problems later.  You would want to do the entire 4" pour at once as well.

If you are going to cover with carpet, then you should be fine for years to come!  

Concrete/Flatwork

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Volunteer


John Hutchins

Expertise

Questions regarding concrete damage and how to protect concrete from damage. When repairs can be made or when it's time to replace

Experience

My area of expertise is in concrete sealing and protection, along with the associated causes of concrete damage.

Organizations
BBB

Education/Credentials
Various training classes over the past 7 years. Real life applications and inspections of 1000's of concrete projects.

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