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Discussion Starter · #1 ·
I am planning an addition to my home that will require some 3/4" exterior plywood to be used for formwork. About 30 sheets. I am wondering whether (perhaps if I apply thomson's waterseal or another product to the inside of the forms) they would be suitable for my roofing and my attic flooring after I strip the forms and allow them to dry (in our south Louisiana heat). Any thoughts ?
 

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Form release agents are what you should be looking for, no matter what. There are many different kinds and grades, however. We usually pick ours based on mix, temperature, and finish required. Call your local mason's supply store, and they should be able to pick something out based on what you tell them.

However, there's typically an oil and voc component to the release agent, so it wouldn't be suitable for re-use. Plus depending on the type of release agent and how much you put on, it might stink up the attic.

You should think about just renting the forms. We have a local supply house in our area called AH Harris, and we rent Symons brand forms from them.
 

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You might look into renting forms. It might be cost effective, especially if the plywood is not reuseable.
Ron
 

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Been there, done this: place 6 mil plastic sheeting on the boards you want to save. Staple often, very often so the mud won't tend to tear it off. We have used this to save 3/4" plywood we wanted to use elsewhere, but not for roof decking, we just don't use 3/4" for roof decking here. The wood we saved we used on another home for floor decking. It can be done. Good Luck , David
 

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Buy the right product instead of messing with plywood. BB plyform, MDO, or HDO plywoods will perform best in this application because that is what they are made for. Form release oil is a must. Plastic? No thanks.

I've got to ask...
What on earth are you forming up with 30 sheets of plywood? If the answer is foundation walls do yourself a favor and do some research on wood form design. Plywood forms are RARELY used in residential construction because of the staggering amount of framing necessary to keep them from bowing or even blowing out. The pressures exerted by wet concrete at the bottom of an 8' wall are incredibly high and I've been on a lot of jobs where people didn't realize that and lost the entire wall during the pour. Just be sure you know what you're doing and realize that wet concrete weighs in excess of 130 pounds per cubic foot.
 

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Buy the right product instead of messing with plywood. BB plyform, MDO, or HDO plywoods will perform best in this application because that is what they are made for. Form release oil is a must. Plastic? No thanks.

I've got to ask...
What on earth are you forming up with 30 sheets of plywood? If the answer is foundation walls do yourself a favor and do some research on wood form design. Plywood forms are RARELY used in residential construction because of the staggering amount of framing necessary to keep them from bowing or even blowing out. The pressures exerted by wet concrete at the bottom of an 8' wall are incredibly high and I've been on a lot of jobs where people didn't realize that and lost the entire wall during the pour. Just be sure you know what you're doing and realize that wet concrete weighs in excess of 130 pounds per cubic foot.
And KC's being generously optimistic here. We have always figured for up to 20 pounds more in our pours..... That's 4,000 pounds per cubic yard. This stuff can hurt you, big time. We once lost three men down a stairwell shaft because of them rushing to yank the lever on a 1/2 yard bucket from about 4' above a formed and braced 3/4" plywood deck.

It took out a 12' hole in the forms, and dumped them and the concrete and all the splintered form boards almost 50' below. Thank God the stairs were in place, and it was nothing more serious than a wild, bone breaking ride down the bumpy steps for them. Everyone lived, but no one survived without several broken bones each.

And we had a 1 yarder and a 2-1/2 yard bucket on the job. Imagine what one of them might have done?

Don't underestimate the force behind that grey oatmeal.
 

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Willie,

If this site had the "thank you" button like the contractor site has, I would have clicked it.

Thanks for the war story and caution. You too, KC.
 

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Right on about that concrete pressure and blow-outs.

I'm a homeowner that does mostly short retaining walls. I painted my form panels with a couple of coats of polyurethane. They have been through a dozen pours with a couple of re-paints and still look good. I use full strength mop-n-glow for a form release, applied and allowed to dry before assembly (none gets on the footer or steel). The small amount of concrete that sticks is pretty easy to scrape off.

 

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Discussion Starter · #9 ·
Thanks for everyone for their suggestions.

Regarding the blowouts... I was originally going to stack ICF for my (unfinished) basement myself, so that I could save some money from hiring someone to do all the formwork. Then I came across Spider-tie and it looks like it will work well for my application. And since I don't need the insulation, it will save me some money, even if I can't reuse the plywood.

Wall height = 6.5' in some places, 4' in others
Wall length = about 82'

(roughly 30 sheets with scraps left over...)
 

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Right on about that concrete pressure and blow-outs.

I'm a homeowner that does mostly short retaining walls. I painted my form panels with a couple of coats of polyurethane. They have been through a dozen pours with a couple of re-paints and still look good. I use full strength mop-n-glow for a form release, applied and allowed to dry before assembly (none gets on the footer or steel). The small amount of concrete that sticks is pretty easy to scrape off.

Few people realize this, and I know I will hear all sorts of "Gasps" from stating this, but it is really not a big deal if it gets on the rebar. The rebar is built with those ridges cast into it to lock it in place. It does not rely upon surface tension. If it did, all the rust that is usually on rebar would cause all of it to fail everyday.

Truth be known, rebar doesn't even have to be tied together to develop any strength situations. It just gets tied to keep it in place, relative to the rest of the rebar and the forms. Basically, so it doesn't shift during the pour.
 

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Willy T is right, it's not a big deal on the steel or even on the footer where the footer is tied to the wall and has a keyway. I guess I like the dry mop-n-glow because it is less messy and can be done well before form setup. Important to me as a one man crew. And the mop-n-glow works well on the plastic pipe spacers I use in my system; they tap out easily after the forms are removed.
 

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Willy T is right, it's not a big deal on the steel or even on the footer where the footer is tied to the wall and has a keyway. I guess I like the dry mop-n-glow because it is less messy and can be done well before form setup. Important to me as a one man crew. And the mop-n-glow works well on the plastic pipe spacers I use in my system; they tap out easily after the forms are removed.
I have to admit that I will probably be using the Mop-n-Glo method sometime in the future. :thumbsup: I already use "Pam" on my car grilles and hoods to keep the Love Bugs from sticking. Kinda works. :wink:
 

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I don't want to rain on anyone's parade, but Mop'n Glow costs 5 times as much as the releasing agent I use with bare wood forms, and I apply it with a garden sprayer.
 

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Right on about that concrete pressure and blow-outs.

I'm a homeowner that does mostly short retaining walls. I painted my form panels with a couple of coats of polyurethane. They have been through a dozen pours with a couple of re-paints and still look good. I use full strength mop-n-glow for a form release, applied and allowed to dry before assembly (none gets on the footer or steel). The small amount of concrete that sticks is pretty easy to scrape off.

That's an admirable form set up for a DIY'er. You might want to incorporate standard whalers and wedge bolts. It would cut the time of assembly down by an order of magnitude. Plus whalers and wedge bolt hardware cost a lot less than the all thread I see in the picture.

Also, how much overlap do you have on the rebar?
 

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Mop--n-Glow probably is more expensive. But for a DIY job it's a tiny cost of the wall.

I've watched more than a few walls formed with snap ties. For 8 ft walls it would be much faster than my bolt together forms. for the 32" wall I build, I'm not so sure the commercial methods would go much faster. But what ever, as a DIYer it's my time I'm wasting. But with my system, all of the supplies can be had at Home Depot and the only thing not re-usable is the concrete and steel. Even the plastic pipe spacers get used again. The pattern of holes left in the wall are used when I need to bolt re-usable step formers to the side walls. It makes steps an easy process; bolt on the form and insert the riser boards.

For taller walls, I have to do it in two steps, resetting the forms on top of the first pour.

It's a DIY homeowner system for a one man crew. Well, I do get one of my sons to help with the pour. I've done over 350 lf of wall with about another 50 ft to finish the project. Since I have re-used the forms many times, my total cost for the wall is down to about $4 per face foot.

Some wall after forms removed before spacers were tapped out.

 

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Well, it IS a one-time cost for the threaded... especially when most of your pours are small, not requiring too many of them... and reusable. Snap ties are gone when they're used. Cost might easily balance out.

And Henry Ford's thinking on the bolt holes being ready for another kind of use is pretty neat. Good planning.
 

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The lower holes in the wall serve as weep holes. The step forming goes as shown below. First the sidewalls are poured on a footer that extends into the step area. Extra vertical bar is placed in the footing to tie the steps.

The re-usable step forms are then clamped to the wall and adjusted to a position slightly above the desired step pour. Note that the plywood panel has 2x4 cleats with an angle bracket attached. Once the form is in position, hoes are drilled from the backside of the wall and bolts are used to secure the form in place.

Riser boards with an angled bottom are clamped to the angle bracket and then tapped into perfect position. Screws are used to secure them. Note that the risers press against the 2x4 cleats to carry the concrete load. Ready to pour.

 
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