Need Help Framing a Turn-Down-Slab

LittleBittyBigJohn · Aug 14, 2023

If I'm understanding correctly I'm just driving in 2x4 stakes on the outside of the form. If that's the case is there any worry about the footer blowing out as thin as the dirt will be?

paulsharvey · Aug 14, 2023

Also, I dont know if You are pouring, or hiring that out, But, it's better to pour a bit drier (lower slump) and work a bit harder on the pour, than pour wetter (high slump), have an easier pour, and longer finish time, as well as lower final strength. A 5" slump is 100% workable, maybe 6" with the footers and bars, but don't let anyone tell you it has too be an 8" or higher slump. Seen plenty of guys that order a 6", and immediately, without even seeing g the mud, flash the driver, add 20 gallons...

LittleBittyBigJohn · Aug 14, 2023

I'm hiring out the pour and finish. I have a group lined up for $1,500

paulsharvey · Aug 14, 2023

LittleBittyBigJohn said:
If I'm understanding correctly I'm just driving in 2x4 stakes on the outside of the form. If that's the case is there any worry about the footer blowing out as thin as the dirt will be?

View attachment 816031

Not really, but if it is an issue, add a kicker, or a 2nd stake back a couple feet, and a board from rear stack to front stack, angled. Also, steel stakes are easier to drive and it would be less issue. The round style are 5/8" diameter, a out 16-24" long, there is also a flat style, that's about 3/8" thick x about 2" wide. Both styles drive Way and pull way easier then 2x4s, and have pre-drilled holes for your duplex nails. Not overly expensive, but a couple dollars each will add up, if you never need them again.

paulsharvey · Aug 14, 2023

Seems steel stakes have gone up too... But really, $3.60 per stake isn't that much more then buying 8 ft 2x4s to cut up into stakes. And you can drive them with a framing hammer. That's not going to happen with 2x4 stake, that's 8 lbs sledge time if you want to drive them very deep. They dont hold equal to a 2x4, hence the 24" vs 48" spacing.

LittleBittyBigJohn · Aug 14, 2023

I went by the lumber yard in the way home from work. They said to form first then dig the footers. Said if i dig footers first the stakes will blow out. Does that make sense?

It sounds good but I'll have to be creative with the machine to get it straddled over the forms.

Also they said use a rebar chair for the lower 2 rebar runs. Then another chair on top of that run for the top 2.

paulsharvey · Aug 14, 2023

LittleBittyBigJohn said:
I went by the lumber yard in the way home from work. They said to form first then dig the footers. Said if i dig footers first the stakes will blow out. Does that make sense?

It sounds good but I'll have to be creative with the machine to get it straddled over the forms.

Also they said use a rebar chair for the lower 2 rebar runs. Then another chair on top of that run for the top 2.

Yes. You will have to 'clean' the sides up with a flat shovel after digging with the machine, unless you are just plain a stud hoe operator.

As for the dual chairs, I guess that would work, but you will definitely need to wire tie the top chair to the bottom bars, or it will fall off, especially when you start pouring.

Do you plan to be onsite when they pour? I would definitely try, and I know it might be uncomfortable, but don't be shy telling them to pick up the wire, if it's not supported well with wire chairs or wired to bricks. The chairs are like $0.60 each, in packs of 100, and they really do help keep the wire off the ground. Wire under the concrete does nothing, but does wonders when it's in the center. Engineers will tell you it just prevents cracks during curing, but it does more than that...

For the machine, you can rotate the cab, then off set the hoe, and dig more or less straight. See below video, around 4m33s, if you aren't familiar with what I mean.

View attachment 816093

LittleBittyBigJohn · Aug 15, 2023

I had a couple of fails yesterday after work. I started laying out my corners using 18" rebar as the corner pins. The ends of my tapes are too small to go around the rebar. I got one wedged on there good enough to hold and ended up tearing off the tip. Then I decided to go ahead and start my batter boards. I cut a 2X4 at an angle and started pounding. Started with my 4lb shop hammer then went to my 12 pound sledge. I didn't get it but 6-8" in the ground. There is no way I'm going to be able to drive them farther than that.

Couple questions, I don't want to buy the metal stakes if I can help it, they are expensive. How far do I need to get the 2X4 stakes in the ground around my forms. I assume I need them pretty deep since the dirt will be so thin once I dig the footer in front of them. Also, I can probably get them deeper if I rip them in half, making them 2X2, will that be ok?

I tend to overthink everything but this is a big expense and I have literally zero experience with this.

paulsharvey · Aug 15, 2023

You want your form board to be able to withstand the force of the concrete weight pushing out. That's going to be in the neighborhood of 50 lbs per linear foot I'm guessing, depending on wet it is, ect. Your soil conditions really determine how much you need to stake. Ripping 2x4s, to 2x2s might work, and is common practice on sidewalks/driveway pours, where you are holding back 4 or 6" of concrete. You can always throw fill on the outside of the form boards to provide backing support. I can't really advice beyond that, other than, the time to add stakes is Before a blow out/bow.

Edit: don't know if most people can picture how heavy a Cubic Yard of concrete is; think of 42-80# of quickcrey, Plus water, and that's a single yard. Now, you aren't supporting nearly that, but you are fighting some real weight wanting to push out. Also, does a 1" bow out in a 40 ft wall cause you great concern? Maybe, Maybe not; but a 3 or 4" Bow might. Depends on what/how you are building on top of the Slab, as well as your personal level of acceptance. You don't want to know how out of square/level/straight many new construction homes are.