Concrete question

[Skyjack]

Hi all, I am getting ready to build again and this time I am building with a basement.
My question is this, I plan on building my forms with 5/8 inch plywood or osb with 2X4's screwed every16 inches to the plywood as bracing. I will tapcon them to the footer and add more bracing after the forms are stood up. Will 5/8 inch plywood be strong enough for the forms?
I do plan on using the plywood for roof decking and the 2x4's for wall framing.
Thanks

 

[Bondo]

Hi all, I am getting ready to build again and this time I am building with a basement.
My question is this, I plan on building my forms with 5/8 inch plywood or osb with 2X4's screwed every16 inches to the plywood as bracing. I will tapcon them to the footer and add more bracing after the forms are stood up. Will 5/8 inch plywood be strong enough for the forms?
I do plan on using the plywood for roof decking and the 2x4's for wall framing.
Thanks

Ayuh,.... You can use 1/2" plywood, so long as it's properly braced, 'n supported,...

 

[starquestMM]

The strength required depends on height. The taller the wall, the more fluid pressure, the thicker the material.

How tall?

 

[kd3pc]

how tall and how much "footer" compared to slab.

12-14" centers well braced and less than 18-24" tall, you should be OK, anything more you will need more bracing or bands from 2x4" then braces...

 

[ForceFed70]

1st off, don't use OSB - You will have a heck of a time trying to get the forms off once cured. Even with plywood you should paint (or ideally soak) is diesel to help prevent sticking.

Most people choose to use a thicker ply and avoid the 2x4 bracing. You were planning to use concrete ties right? Thicker plywood with concrete ties will cost a little more, but will save a lot of time.

Also - you may want to look into renting forms. Typically they are pre-oiled, pre-slotted for concrete ties, and cheaper than buying the materials to make your own.

 

[41ratrod]

I've built a lot of forums and it is cheaper to rent in the long run.
I'm so glad I'm not doing that type of work anymore.

 

[Skyjack]

I am going 8 feet walls and the footer will be 24 inches wide. I have also thought about pouring it 4 feet tall and after it cures pour another 4 on top of it (with a key way) so there would not be as much pressure.

 

[kd3pc]

I am going 8 feet walls and the footer will be 24 inches wide. I have also thought about pouring it 4 feet tall and after it cures pour another 4 on top of it (with a key way) so there would not be as much pressure.

8' concrete wall? How big will the slab be?

Rent the forms and a crane....single pour unless you have a good engineer on site and can make sure the two will be plumb when complete. Lots of steel especially the corners and tie in to the footer stubs/steel

You will need vibratory stingers and true pour forms (two sided, through tied and anchored to the footer with stubbed rod) along with some way to hit the forms from the truck (long chute, or usually these are pumped? Plywood forms won't make it. They often "float" if they don't buckle or puff.

Wow, this is a fairly ambitious plan for DIY, friends in the poured walls business?

 

[Skyjack]

When poured the floor (slab) will be about 30' X 50'

 

[pstnbly]

Way not enough form there for the job. My form panels are 1" HDO marine plywood drilled for 6 ties each. Without the cross ties, dogs and whalers there is no way they will support a 4' pour let alone an 8' pour. I pour 10" thick wall minimum and you can't appreciate the pressure concrete exerts on formwork unless you have experience. I've seen many pours go very bad by people who should know better.

As ratrod said either rent modular forms, or sub it out. Wall pours are professional level work and the lessons learned are expensive and painful.

 

[Krodad]

Or use ICF's

You still have to brace ICF's of course, and they will cost a little more, but when hou factor in the insulation cost, form rental, wasted lumber in wood forms, it's usually pretty close to a wash and you'll have an awesome basement. I would suggest ICF all the way to the roof actually. If it's a ranch I'd go either 8" core for the basement and transition to 4" core for the 1st floor, or 6" core from footing to roof, bllon structure with the ledger hung on the inside.

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[rburke65]

Well you may as well rent the forms and save yourself some head aches...you are going to buy the concrete anyway....I'm thinking unless you have done this before, I'd sub it out.....

 

[ConCretin]

Based on your post, I would respectfully suggest that perhaps you should sub this job out. As mentioned by others, concrete exerts tremendous pressure on formwork and if they aren't constructed properly you'll end with a disaster.

Concrete pressure is a factor of height (not thickness) and can be calculated by multiplying the height by 150. The pressure on the bottom of an 8' form is 1,200 pounds per square foot. Without getting into other factors such as placement rate, that a lot or pressure. The forms you are describing won't cut it.

Forget TapCons and braces. You'll need some sort of internal tie at 12 to 24" on center in both directions depending on the type of tie and form construction - probably closer to 12" based on your proposed materials. Braces should only be used to align the form.

If you decide to proceed, do a lot more research and try to find some professional help (not just the concrete kind).

 

[Skyjack]

Thanks for all the suggestions and info, I will look for forms to rent.

 

[raddksn]

Or use ICF's

You still have to brace ICF's of course, and they will cost a little more, but when hou factor in the insulation cost, form rental, wasted lumber in wood forms, it's usually pretty close to a wash and you'll have an awesome basement. I would suggest ICF all the way to the roof actually. If it's a ranch I'd go either 8" core for the basement and transition to 4" core for the 1st floor, or 6" core from footing to roof, bllon structure with the ledger hung on the inside.

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I did this, I used T F System insulated concrete forms very nice system and user friendly. As said before proper support and bracing is CRITICAL!!!!

 

[volleyball]

For me, ICF's mean an engineered plan. Was not cost effective. I'd sub out a poured wall or do block if I were to do it myself. You can grout the blocks