How thick of plywood is needed for concrete forms? What spacing on the bracing? Pours could be up to 10ft tall.

Will plastic sheating separate from the concrete if it's used to protect the forms? If not, what can be used to coat the forms that isn't toxic?

Any good online info on the process? Haven't been able to find much.

Thanks

here is an idea:

http://spidertie.com/

good luck
Adi

1/2" plywood is commonly used for concrete forms. But it needs to be well supported. Are you asking about internal or external bracing?

What are you trying to build?

I'm interested in being able to run some numbers for building walls. External bracing.

Try this:

http://www.gp.com/BUILD/DocumentVie...entid=3838

Be careful if you DIY.

Bruce

Thanks Bruce, that's great info.

To answer your other questions, there are special form release products that are sprayed onto the forms to prevent sticking. There are low/no VOC products, but look at the mfgr info and MSDS sheets for the specific products.

I would not recommend poly sheeting as it will not release evenly. We have cast slabs on grade on poly sheeting and then excavated under the slab (in a process called "top down" construction). Removing the poly is always a PITA. These are typically exposed garage ceilings. If the concrete is not exposed, the appearance should not be a problem, however.

Bruce

As shown on the APA Concrete Forming guide linked above, it takes A LOT of 2x wood external bracing when forming walls with plywood.

From the guide above, assuming 1/2" plywood with the face grain across the supports, 70F concrete, and a slow 2ft/hr pour rate, you will need a vertical 2x4 support every 12" with a double 2x4 horizontal support (wale) approximately every 32". If you go with 3/4" plywood instead of 1/2", you could reduce the vertical support spacing to 16" oc, but would likely need to go with 2x6 or decrease the spacing of the horizontal walers. This is in addition to the internal form ties holding it all together.

The reason I asked what it is you are building was whether or not one or both sides of the wall will be insulated. If so, I may have a suggestion that you had not considered before.

I'd love to hear new ideas! The wall will be insulated.

Describe your project. What are you trying to accomplish?

One obvious option if you want an insulated concrete wall is Insulating Concrete Forms (ICF). Have you considered these?

Posted By Vermonter on 22 Oct 2010 12:40 PM
How thick of plywood is needed for concrete forms? What spacing on the bracing? Pours could be up to 10ft tall.

Will plastic sheating separate from the concrete if it's used to protect the forms? If not, what can be used to coat the forms that isn't toxic?

Any good online info on the process? Haven't been able to find much.

Thanks

the first job I ever built in Florida 26 years ago wa a 10 unit - 2 story condo building, the second floor was a cast in place 6" concrete floor. We used 5/8"CDX plywood, with double 2x4  support beams and many rented adjustable stanchion posts.

after the floor cured and we removed the posts, 2x4's and plywood, we paid laborers to clean up plywood and 2x4's by removing all nails.
We reused the plywood for the roof deck over trusses and all the 2x4's were used for the interior wall framing, thre was very little waste

Posted By arkie6 on 23 Oct 2010 09:11 PM
Describe your project. What are you trying to accomplish?

One obvious option if you want an insulated concrete wall is Insulating Concrete Forms (ICF). Have you considered these?

I'm planning a house. Yes I'm strongly considering ICF. I don't like that EPS is used in most of them, and Dursiol is expensive, so I'm  looking into other ways of doing concrete.

What is the concern with EPS? What about XPS?

I'm trying to find ways of building that use less nasty chemicals and energy. Also fire resistance is a concern, although I know that EPS/XPS between concrete and drywall should be pretty safe. The exterior would have a good air supply if it somehow caught fire, as I would likely be using fiber cement siding with a rain screen gap.

I'm not saying those are "deal breakers" for ICF, I'm just tossing around ideas and seeing what else is possible.

If you pour a solid concrete wall using plywood forms, how were you planning on insulating?

Perhaps setup something similar to Larsen trusses and do 6+ inches of dense pack cellulose on the outside, with an insulated roof deck. All the insulation could be kept outside the structure and minimize thermal bridging.

If you are near a metro area you can rent concrete forms. They will pre-coat and drop the form in your excavation on a special rack. When you're done relad the racks and they will pull them back out of the basement.

Might find this to be the most economical solution if you have to pay labor costs to clean 2xs and plywood.

Vermonter, you may as well go over and look at the thread started on the toxicity of HBCD on the Insulated Concrete Form section of this site. It is beginning to look like the tradition EPS of and ICF form really are not that toxic. I would opt for one of the traditional ICF blocks, though I am certain that I am a little biased. Just thought I would mention it.

Hi,
As what my home build the builder use 1/2" thick of plywood and 2" thickness for the braces...

Buildblock has a form that they use that has removable tabs that attach to plywood, or another panel material. After the concrete has set, they leave small holes (1/2" if I remember correctly, maybe 1/4?) that can be patched, or they can be left in place to mount cladding. I don't love the foam idea on the interior either, so I've looked at those - for me, I just like concrete stain. Then, you'd have your 2.5" eps on the exterior, which qualifies as both an air and water barrier, but is still vapor permeable. I think the resulting R-value hovers around 10, but I don't know what the code requirement for mass walls is in Vermont. For the zone I'm building in, that doubles the required building envelope insulation.

The DIY factor appears much more manageable with this, and their recommended bracing products aren't crazy expensive either (and resale after finish is always an option). One of their bracing options also provides a deck for placing blocks and rebar higher up on the wall - I think both of them do.

I'll go ahead and add a grain of salt to this since I take "novice" to a whole new level - I've just done a lot of reading and research over the past two years for the home we're building.