# Extending Concrete Patio Slab



## bobo (May 17, 2005)

hello,

ok, first of all, im not a mason, by anymeans, but i think i have an idea of what im doing. i want to extend the patio concrete slab that is currently there. i didnt dig yet, but it looks to be about a 3" slab of concrete, judging by how deep the water drain in the slab is set in. the exiting slab is 10'x10'. i want to extend it another 10'x10'. now the questions!
1) do i use item #4 for a base before pouring the concrete? or just #2 stone?
2) should the dirt/sand be tamped berfore putting in the item#4 or stone?
3) when i build the forms, i should make sure they are flush with the existing slab, and tapered away from the house, correct? and what should the pitch be?
4) should i put a piece of that felt like board between the existing slab, and the new slab for exspantion?
5) would it be fesible to use the ready mixed concrete in a bag for this job? or buy the morter and the sand in bags, and have stone/item#4 deleivered?
and how many bags of premixed, or how many bags of sand, morter, and how much stone/item#4 for will i need? if "I" mix the concrete, what is the formula for the mix?
how much water should i use?
should i layer wire mesh over the stone/item#4, or under? should i use the wire mess that looks like fencing?
6)after i pour the concrete, i pull the wire mesh up into the concrete so it is somewhat intwrined in the mix, and not lying on the bottom, correct?
7)before i rake the concrete, should i tap on the sides of the form, all the way around to release as much trapped air as possible?

well, please let me know what u all think! thank u, any help will be greatly appriciated!

bob


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## Tscarborough (Mar 31, 2006)

What is item #4?

Assuming that you will have to dig, not raise the area of your new patio, here is what I would do:


Remove the sod and dirt to a level of 8" below finished grade, and about 3" past your 10x10 area.

Place and compact 4" of road base.

Form your perimeter with 2x6, staked 24" O.C. and backfilled against the forms.

Cut 10x10 10/10 wire to fit the area within 1" of the edges. Buy enough concrete brick to support the mesh off the base.

Against the old slab, drill 1/2"diameter holes , 6" deep every 12" (nine holes). Grease a 3/8"x12" rebar and stick it in the hole so that it has a small amount of space at the end in the slab.

To pour it, you are looking at 42 80# bags of concrete mix at least, so it is doable, provided you have a 2 bag mixer and can set it right next to the slab. Expect to work your ass off for about an hour and a half, along with at least 2 of your friends. That is what I would do.

To finish it, be sure and edge it, and cure it with either plastic or a sprinkler for a couple of days.


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## bobo (May 17, 2005)

*Extending Concrete Slab*

tscarborough,

thanks for the info! item#4 or maybe its just item4, is used as a base under blacktop. it is like a fine crushed stone, with a binder added to compact better. what do u mean by "road base"?and when u say "10/10 wire, do u mean the wire mesh that comes in sheets? or in a roll? and drill holes into the side of the exsiting slab, so that the rebar is 6" into the exsiting slab, and 6" sticking into the form area so both slabs will be held together when the new slab is cured? and do u mean acually "grease" the rebar before inserting into the slab??? can i use rebar for stakes too? can i use red bricks about 3" thick with holes in them to hold the wire mesh off the ground? i have alot of them kicking around! sorry if im asking anoying questions, but i dont have much experience in this field, but beleive i could pull it off, and maybe save some money in the long run...bob


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## Tscarborough (Mar 31, 2006)

Item4 is roadbase.
Wire mesh, roll or flat. 10/10 is the guage of the wires, 10x10 is the wire spacing.

Yes actually grease the rebar, but only on one end, and make sure the dowels are horizonal and perpendedular to the joint.

Rebar stakes are fine as long as you backfill against the forms.

The red brick is fine.


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## Teetorbilt (Feb 7, 2004)

Ts, why the grease? I have done this many times minus the grease and I don't grease any other rebar. IMHO, it would loosen the interface.


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## Tscarborough (Mar 31, 2006)

It allows the two slabs to move independently while tying them together. It is overkill, but is also cheap and easy.


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## Mehalt (Apr 17, 2008)

I am in North Texas - where the ground is notorious for moving - and planning to add an extension patio adjacent to the existing walkout area to the back-yard. The patio will connect to the walkout area.

I can tie the foundation to the new patio using this re-bar method, but is this all I should do to prevent the patio from migrating away from the house foundation? Also, If I do this, I assume I still need to use the expansion foam between the new and existing concrete?

I am a little cautious since I have recently relocated to his area. I have heard many horror stories about foundation problems and concrete pads moving and cracking. Any help on these particular issues would be great help!

Thanks

Mehalt


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