# pouring concrete between existing walls questions



## oh'mike (Sep 18, 2009)

I'm not a concrete guy---

What is your frost depth?

What 'tiles' are you talking about?


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## Daniel Holzman (Mar 10, 2009)

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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## tycobb (Jul 25, 2010)

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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## Daniel Holzman (Mar 10, 2009)

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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## tycobb (Jul 25, 2010)

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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## Canarywood1 (May 5, 2012)

tycobb said:


> 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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## jomama45 (Nov 13, 2008)

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...........


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## stadry (Jun 20, 2009)

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 important knowing where YOU are :thumbsup:


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