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Old 05-05-2013, 04:34 PM   #1
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pouring concrete between existing walls questions


I want to pour concrete in this open part of my house. Since it already has the roof over it, it will be an easy addition.

Pour concrete, put up a wall. My question is about pouring the concrete. I had a company give me an estimate.

Their idea was to dig a footing across the front, and screw angle to the tile along the side wall and rear wall to keep the slab from settling. I thought about drilling past the tile into the existing slab and putting rebar pins to hold it. (the house is on a slab. no basement or crawl space).

The problem with that is on the garage side (the right side) there is no concrete behind the tile. Another idea I heard from someone is to break the face of some of the tiles open, so the concrete will will flow into the tiles and hold that way. Also, how do I screed it and make it all level if I'm using the exist walls as a form and don't have normal forms go on top of?

I decided to do this myself, so I'm looking to find out which of these ideas make sense, or any other good ideas. I've got an old timer neighbor that has many years of experience in construction to help me, so I'm not going it completely blind. Just wanted some ideas before I hear his. Thanks, and sorry for the long post.


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Old 05-05-2013, 05:28 PM   #2
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pouring concrete between existing walls questions


I'm not a concrete guy---

What is your frost depth?

What 'tiles' are you talking about?

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Old 05-05-2013, 05:52 PM   #3
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pouring concrete between existing walls questions


The best way to keep a slab from settling is to make sure it is placed on a good foundation. A good foundation for a slab is at least six inches of compacted crushed stone over firm mineral soil. If the concrete is going to act as a support for structure, the footers need to extend to at least frost depth. Your local building inspector will know what frost depth is for your region.

If the slab is not acting as a structural support, it can be placed on grade (a floating slab), but you need free draining soil below it down to frost level. Free draining means coarse sand, 3/4 inch stone, or crushed stone. If you place your slab on silty soil, or certain clays, it is prone to heave in the winter.
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Old 05-05-2013, 08:07 PM   #4
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pouring concrete between existing walls questions


The tiles I'm talking about are the tile foundation blocks. I think the frost depth is 36", I would have to check to be sure.


When you say "footers" are you saying they should be on all 4 sides, or just along the front. There is currently crushed rock there on dirt that has been undisturbed for a while. There is room to add more.
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Old 05-05-2013, 08:11 PM   #5
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pouring concrete between existing walls questions


The definition of a footer is a support pad set below the level of a slab on grade. Typically a footer is concrete, and is used either to support a column (often a square footer) or the basement wall (usually a rectangular footer). I cannot tell from your post if you plan to support any load with your slab. If you are, you need footers. If you are not, you can build a slab on grade.
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Old 05-05-2013, 08:23 PM   #6
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pouring concrete between existing walls questions


I know what a footer is. I thought one across the front would be sufficient with the other 3 sides being supported by the existing foundation be means of putting rebar into the existing foundation. That is basically my question, how to attach the new slab to the old for support. I want to put a stud wall across the front once the concrete is pour. It will be a new interior room to my house when done. therefore it will be supporting some weight. As much weight as any average household floor supports
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Old 05-05-2013, 08:46 PM   #7
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pouring concrete between existing walls questions


[QUOTE=tycobb;1173369]I know what a footer is. I thought one across the front would be sufficient with the other 3 sides being supported by the existing foundation be means of putting rebar into the existing foundation. That is basically my question, how to attach the new slab to the old for support. I want to put a stud wall across the front once the concrete is pour. It will be a new interior room to my house when done. therefore it will be supporting some weight. As much weight as any average household floor supports[/QUOTE


One across the front is what you need,if the frost line is 36" then you need to go down 42" with concrete for your footer,and there's no need to pin it to the existing floor,the footing will be supporting the wall you want to add.
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Old 05-05-2013, 09:20 PM   #8
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pouring concrete between existing walls questions


Pretty simple addition really:

- Excavate front footing, which is going to be the hardest part due to access.
- Pour a footing matching the height of the existing footings, doweled together.
- Build a concrete block or poured concrete stem wall connecting the existing, again doweled in.
- Allow for a 2" wide by 4-8" high floor ledge on the interior of the new stem wall.
- Dowel into the existing floor on the 2 sides. The spans are short, a little re-enforcement and the third wall w/o any dowels will easily span.
- Pour and finish the floor inside the addition. You'll likely want to open the doorway up first to make sure the new floor matches the existing floor height so there's no transistional difference...........

Last edited by jomama45; 05-05-2013 at 09:27 PM.
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Old 05-06-2013, 04:07 AM   #9
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pouring concrete between existing walls questions


remember this part, cobber ?

'oh'mike - Super Moderator - New members: Adding your location to your profile helps in many ways. '

he would rather have a pic of his family there but its importantknowing where YOU are

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