Filling concrete footing on uneven ground

[black_edelweiss]

Im building a 24x32 A-frame, and preparing to pour the footer which is about 18wide x 20"deep. The ground is on a slight downward slope and i need advice on how to pour it so its perfectly flat. Im doing the mixing myself, as its too far out for a concrete truck.

Do i just dig the bottom of the footing so its flat? Problem with that is there are a lot of medium size rocks throughout it which makes it very hard to get it all flat.

Do i use boards that span the length of the footing that are level and fill inside those?

[Don_P]

The bottom of the footing trench should be as flat as possible, it may slope up to 10%, if steeper install steps. I'm not sure what a medium sized rock is, things protruding up into the footing can cause a stress concentration under load and cause it to crack.

If the trench is the form rather than having form boards set to elevation that you can screed from, I'll drive pins every 4-6' down the center of the footing trench setting the top of the pin to the top of footing level.

Remove all form wood when complete, termites can smell rotting wood.

[black_edelweiss]

Thanks for that, the pin idea will work. When i install the vertical re-bar, how tall does it need to be? Do i drive it into the ground or do i form a 'J' hook around the horizontal re-bar in the footing? I'll be laying 8ft tall wall of cinder blocks ontop of the footing

[NathanS]

J hook tied to the horizontal rebar. By tying the walls to the footing with rebar you greatly improve resistance to wall overturn.

The theory is that if the rebar is in contact with the ground, it will get wet and rust away over time.

You want the rebar to run all the way up to the top of the wall where you could consider running horizontal rebar through the top course, with the verticals tied into that. You don't need to run the rebar 8 foot high in one shot, you can do a few feet, then lay blocks until you're up near the top of the rebar, then tie another piece on with a certain amount of overlap. The rule for overlap is something like 30x the rebar diameter. So with #4 (1/2 inch) you would have 15 inches of overlap. I can't remember if 30x is the actual number, you need to double check that one for sure.

The IRC code has tables that will pretty much tell you most of what you need to do.

Also since you are doing block you definitely want your footing to be level, or else you're going to be cutting block length-wise to get level. And that would be way worse than getting your footing level, and stepped in units of 8".

[Don_P]

LOL, I was in chapter 4, you know, foundations, under reinforcement, lap splices... "see R611.5.4(1)"  Lap varies by bar size and steel grade...I didn'r know that, I was double checking that it was 20d from my memory, not so anymore. I can't think of a situation where it is not good to deform the end of the bar "Pull this hook out I dare ya"
Good pictures there as well;
http://codes.iccsafe.org/app/book/content/VA/2012_VA_Residential_HTML/Chapter%206.html

Oh, do notice in chapter 4 they want vertical reinforcement very close to the interior, tension, face. In footings keep 3" of concrete between you and the earth. Rust is actually like ice, it expands and spalls the concrete.

[black_edelweiss]

Thanks for the info.

When i start pouring the concrete, should i divide the lengths of the footing into sections or do the whole section at once? Since i'll be using a mixer and doing it myself, do you have any recommendations or tips?

Thanks

[Don_P]

Always better in one go but I've done it a few feet at a time on restorations plenty. 3 of us, 2 men and a boy, poured a bit over a yard this morning, about 2 hours but not at a pace I could do all day. Finished the day in the attic ducking wasps and moving insulation  . All day concrete might have been more fun    I would have some dams and pins ready that will slip over the footing rebar and give you a stopping place if needed.