Pole Barn Slab Forms - Preventing Bowing

[lakeroadster]

How should I support concrete forms to keep them from bowing when the slab is poured?

We are nearing completion of the framing of my pole barn and I have a question for the savvy concrete folks here.

The barn has "splash boards" all around the perimeter. These are 2 x 8's, Pressure Treated for ground contact. These splash boards are the forms for the concrete slab. They are attached to the barn columns using metal brackets so the attachment is very strong.

Unsupported spans of the splash boards vary from 6" up to 13'-6". The long spans are already bowed... just due to the nature of a long board being bowed. They were placed such that they bow into the barn.

The slab will be 5" thick, Building is 30' x 44'.

The colored metal building sheets terminate on the outside of the splash boards, therefore placing exterior supports on these boards could be problematic.

Options:

Could metal stakes be driven into the ground on the inside of the building and then wired to the splash boards by drilling through the splash boards?

Would a better approach be to place 2 x 4's against the lower trim and then drive stakes into the ground to support these?

What would be an appropriate spacing for the supports?

Thanks!

 

[LXCam]

Stake it from the outside. Use some cut up 2X to space it off the sheetmetal siding so you can drive the stake and not damage the exterior. For a 5" slab I'd go no more then every two feet.

 

[lakeroadster]

Stake it.

Understood.......

• To what?
  
• How?
  
• Spacing?

 

[LXCam]

I edited bud, I prematurely posted.

 

[matt_i]

I would keep your supports outside, a 2x2 "sharpened" on a mitersaw or tablesaw makes a nice stake if the ground is soft. If that is just going to splinter, then I would probably go with 1/2" rebar. Drill a hole thru the larger flat side of a 2x4 and pound the rebar thru it. PLace the 2x4 perpendicular to the splash board, and "toenail" with deck screws which can be removed later.

I would spend the time to straighten up the long boards as uncontrolled, you are going to live with it forever more in the concrete.. I like your idea of pounding rebar "stakes" inside the forms, and then also support outside with the 2x to also resist the load from the wet mud. The rebars will just get entombed beneath the slab.

The other idea is to use a 2x4 on edge with the splash board and make a "T" shape, turned sideways. If you spend time to counterbore the short edge and then deck-screw it to the outside face of the 2x8 every 16" to 24" you'll pick up a lot more rigidity and stiffness in the splash board, straightening it (I would set it up with C-clamps or bar clamps and not rely on the screw threads to pull it all up tight). The downside is the holes from the deck screws will remain but if you can live with that imperfection it would save a lot of time.

 

[gpflepsen]

3/4"x1-1/2" wood stakes on the form board, pound in then adjust their tightness on the form by a few hits on the ground right against stake. Put another stake in as a kicker to support the form stake. If you need more rigidity, T a 2x4 as already mentioned about an inch down from the form top. Stabilize the form bottom if you do this.

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[elba]

The men that built my pole barn did it in this order.
1 .Installed poles
2. Installed metal roof trusses
3. Installed metal roof
4 . Poured concrete
5 . Installed metal sideing

 

[lakeroadster]

The men that built my pole barn did it in this order.
1 .Installed poles
2. Installed metal roof trusses
3. Installed metal roof
4 . Poured concrete
5 . Installed metal sideing

Thanks for the reply.

Nice Econoline.

When did they pour your slab? Where are you located?

Winter time here.... need roof, walls and doors so the internal can be heated while slab is curing.....

 

[lakeroadster]

3/4"x1-1/2" wood stakes on the form board, pound in then adjust their tightness on the form by a few hits on the ground right against stake. Put another stake in as a kicker to support the form stake. If you need more rigidity, T a 2x4 as already mentioned about an inch down from the form top. Stabilize the form bottom if you do this.

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Thanks for the reply.

An inch down????? How is that done with the exterior trim in place?

 

[keelan]

Thanks for the reply.

An inch down????? How is that done with the exterior trim in place?

According to your drawing you have 4" of board exposed outside. Put in stakes a foot from the building, use 2x's nailed to the side of the stakes and butted up to the board. They don't need to be attached, you're worried about the board bowing out, not in.

It seems like either were all misunderstanding something, or you're over-complicating a very simple situation.


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[lakeroadster]

... T a 2x4 as already mentioned about an inch down from the form top. Stabilize the form bottom if you do this.

Thanks for the reply.

An inch down????? How is that done with the exterior trim in place?

...... It seems like either were all misunderstanding something, or you're over-complicating a very simple situation.

Think about it.... the outside will need to be back filled with dirt to keep the concrete from blowing out from under the splash boards.

An inch down from?

Maybe if I installed some plastic membrane, stapled to the splash boards, inside the building to keep the concrete from spilling outside, perhaps that would work.

 

[keelan]

Think about it.... the outside will need to be back filled with dirt to keep the concrete from blowing out from under the splash boards.

Wouldn't that fill also stop the boards from bowing out? You're pouring a slab, not an 8' wall. There's not a lot of hydraulic pressure. Your'e acting like the concrete is going to spray out from under your 8" boards. It doesn't take much to stop concrete from leaking out from what is basically a footing. You're looking at about .6 PSI of hydraulic pressure at the bottom of your pour.

[edit] You said 5 inch pour.. that's .4 PSI. I think a fart has more pressure.

 

[sni-per]

Wouldn't that fill also stop the boards from bowing out? You're pouring a slab, not an 8' wall. There's not a lot of hydraulic pressure. Your'e acting like the concrete is going to spray out from under your 8" boards. It doesn't take much to stop concrete from leaking out from what is basically a footing. You're looking at about .6 PSI of hydraulic pressure at the bottom of your pour.

[edit] You said 5 inch pour.. that's .4 PSI. I think a fart has more pressure.

^^^^This^^^^

We pour a lot of flatwork, and driving a form pin every few feet, and then packing dirt against the form, is the best method I know of. If you're worried about your forms blowing out, pour all around the outside first, and then fill the middle. You'd be surprised how quickly concrete will settle in. I wouldn't pour over a 5" slump, and go with a 1% non-corrosive accelerator.

 

[csp]

An inch down from?

An inch down from the bottom of the metal trim. You can have it backfilled, if it isn't already, and just dig out a bit of dirt where the reinforcing pieces will go between the splashboards and stakes.

This still gives you dirt around the perimeter of the splashboards and definitely underneath them.

 

[elba]

I am located in Alabama , 2 miles from the Florida border. No frost here.

 

[lakeroadster]

I would keep your supports outside, a 2x2 "sharpened" on a mitersaw or tablesaw makes a nice stake if the ground is soft. If that is just going to splinter, then I would probably go with 1/2" rebar. Drill a hole thru the larger flat side of a 2x4 and pound the rebar thru it. PLace the 2x4 perpendicular to the splash board, and "toenail" with deck screws which can be removed later.

I would spend the time to straighten up the long boards as uncontrolled, you are going to live with it forever more in the concrete.. I like your idea of pounding rebar "stakes" inside the forms, and then also support outside with the 2x to also resist the load from the wet mud. The rebars will just get entombed beneath the slab.

The other idea is to use a 2x4 on edge with the splash board and make a "T" shape, turned sideways. If you spend time to counterbore the short edge and then deck-screw it to the outside face of the 2x8 every 16" to 24" you'll pick up a lot more rigidity and stiffness in the splash board, straightening it (I would set it up with C-clamps or bar clamps and not rely on the screw threads to pull it all up tight). The downside is the holes from the deck screws will remain but if you can live with that imperfection it would save a lot of time.

Thanks Matt

 

[MagKarl]

I cut stakes out of rebar to support my forms. Remove or just drive them further down after the pour.

 

[lakeroadster]

You said 5 inch pour.. that's .4 PSI. I think a fart has more pressure.

Doing the math, 13'-6" long 2" x 8" with .4 psi = 500 lbs of force.

So you're saying you're barking out 500 lb. farts?

 

[gpflepsen]

It's good to consider what may go wrong during concrete placement and mitigate the issues. If the form board is already warping, a screwed 2x4 on edge can bring it back. Driven stakes with some angled kickers can support and locate the form with no issue. Concrete is not going to flow uncontrollably from any gaps in the form base, if it does you are using way too high of slump. Shovel dirt to cover the gaps and cut off any concrete that does come through with a shovel after it sets a bit.

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[Kevin54]

Just support the board like the picture. By screwing the 2x to the splash board, you can then push or pull the board to where you need, then stake it at the other end so it doesn't move. You will need one between each post for support. As far as the gap outside......backfill with dirt or backfill with stone on the outside. Your concrete will be thick enough that it will roll out a little bit under your splash board, but it will not come squirting out everywhere. A little bit of dirt or stone will help stop it from rolling out. Even though the concrete is heavy, you won't have a lot of pressure pushing out.

 

[gpflepsen]

Just support the board like the picture. By screwing the 2x to the splash board, you can then push or pull the board to where you need, then stake it at the other end so it doesn't move. You will need one between each post for support. As far as the gap outside......backfill with dirt or backfill with stone on the outside. Your concrete will be thick enough that it will roll out a little bit under your splash board, but it will not come squirting out everywhere. A little bit of dirt or stone will help stop it from rolling out. Even though the concrete is heavy, you won't have a lot of pressure pushing out.

Exactly as the picture shows, but I'd angle the stake away from the form so the kicker is tending to get pushed down. Like directional nailing, same concept.

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[Richard Head]

Keep in mind that if your perimeter boards are already warped, and you stake them in place, the boards will eventually pull away from the slab once the stakes are removed. This leaves a gap between the slab and siding. I would recommend attaching masonry wall ties, or something similar to the inside of the boards to keep the wood attached to the concrete.

Dave

 

[keelan]

Doing the math, 13'-6" long 2" x 8" with .4 psi = 500 lbs of force.

So you're saying you're barking out 500 lb. farts?

500 pounds if it's concentrated on a single point. Which it's not.

And 500 pounds if the concrete exerted the same pressure at the top of the boards that it does at the bottom, which it doesn't.

You're looking at 17.4 pounds per foot.

I can't believe I'm still arguing this.

When people do footings, they plop the board on the ground, drive some stakes in, kick some dirt up against it, and get on with life.

 

[TractorJeff]

As far as the boards bowing, it is because its pressure treated lumber rigidly contained at each end. If it was allowed to expand and contract as it gained/lost moisture, it wouldn't be bowing.

 

[lakeroadster]

..... I can't believe I'm still arguing this....

Agreed Rough day in the great white north?

You never did answer the fart question that you started.....

 

[gutted72]

The Guys that did my pole barn told me to place a 3" screw every 8" - 10" on the inside of the form boards at the bottom, this way when the concrete dry's around the screws the boards won't warp. So far I have no boards that have pulled away from the concrete.

Plus I but sand around the outside to help hold the boards in place until the concrete dried.

 

[srleen2]

I just poured my 5" slab on my 36x30 pole building. I didn't stake anything, put some of the item 4 that I used for the base around the outside of the splash board and nothing bowed.

 

[lakeroadster]

I just poured my 5" slab on my 36x30 pole building. I didn't stake anything, put some of the item 4 that I used for the base around the outside of the splash board and nothing bowed.

Item 4......

 

[lakeroadster]

The Guys that did my pole barn told me to place a 3" screw every 8" - 10" on the inside of the form boards at the bottom, this way when the concrete dry's around the screws the boards won't warp. So far I have no boards that have pulled away from the concrete.

................

 

[keelan]

Agreed Rough day in the great white north?

You never did answer the fart question that you started.....

Spent the day in the pouring rain tearing out the remains of a chain link fence. Not at the top of my list of favourite things to do!

Regarding the other question: No Comment!

 

[srleen2]

Item 4......

What don't you get?

 

[rayra]

The OP's question is what the bundles of wood stakes at the big box hardware stores are for. Not just for surveying / grading markers..

 

[csp]

What don't you get?

He's asking what you're referring to as Item 4? I'm curious as well. Was there a list of items somewhere that we all missed?

 

[lakeroadster]

He's asking what you're referring to as Item 4? I'm curious as well. Was there a list of items somewhere that we all missed?

Based on the edit that he did to his post he means Class 4 aggregate? I've heard of Class II and Class 6... but not Class 4.