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I'm wondering what type of plywood is used when building your own forms for concrete walls. Can you use run of the mill 3/4" plywood or is there a special type?

(post #106223, reply #1 of 39)

I'm sure a whole lot of people use regular plywood but you can buy plywood specifically for concrete forms.  The face veneer is smoother and oiled.  The edges can also be sealed.


http://www.tecotested.com/techtips/pdf/tt_plywoodconcreteform


 


 

(post #106223, reply #2 of 39)

1/2" ply will work just fine with the proper panel & walers behind them to support it.


typically you will make panels 12" OC, measuring 10"- 11 1/2" for the first stud, that way you can put your snap ties or taper ties at 24" OC and have them at no more than 12" from the edge of panel.


then walers horizontally also on 24" centers.


you can use oil or form release to make stripping forms easier, then reuse as forms or sheathing etc. 

(post #106223, reply #8 of 39)

Half inch???

I guess that depends whether you are pouring a 24" high 6" wall or a ten foot high ten inch wall

 

 


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(post #106223, reply #19 of 39)

yes well, as i said in my post it also depends greatly on what is behind the 1/2" ply, i would not hesitate to use 1/2" for a ten foot wall, but i would make sure of the framed panels and walers.


my point was it seems to me it is usually the bracing system (skeleton)  that fails and not the skin.

(post #106223, reply #23 of 39)

"it is usually the bracing system (skeleton) that fails and not the skin."

Probably true, depending how you define failure. 1/2" would need whalers at 12"OC or better to prevent deforming which uses extra crete.
That much bracing is a lot of extra labour and materials.

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #106223, reply #3 of 39)

What specifically are you building? Is the surface of the concrete going to be finish? Do you have 1000 lineal feet of wall to form? Or is it a flower box outside the front door for the dw?  MDO (medium density overlay) gives a great finish and can be used time and again, but is touching 50$ a sheet in some places.  3/4 inch shop cutting can be had for less than 20$ a sheet if you don't need everything perfectly square and the finish isnt critical.  If you're forming a stemwall, you can make it 11 1/4 inches tall and use your joists as formboards............

(post #106223, reply #4 of 39)

there some china made plywood for concrete work, it balck coated, not worth anything for using elsewhere. cheaper than regular plywood

(post #106223, reply #21 of 39)

Where you getting MDO for under 50 bucks------ close to 80 bucks in the great north wet.


“The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing.”Albert Einstein

 

(post #106223, reply #22 of 39)

Working for a bridge outfit in OR that buys only shop cuttings

(post #106223, reply #26 of 39)

"Working for a bridge outfit in OR that buys only shop cuttings"


 


What are shop cuttings.  

(post #106223, reply #35 of 39)

shop cuts are sheets that the mill rejected as not square or are  shy in a dimension.  Incidentally, on the engineereing front, white cap and other contractor supply houses have engineers in house that will gladly spec your snap ties for you as well as rent the shoes and cowbells and all the other trinkets you might not want to buy.


Edited 5/13/2008 11:22 pm ET by Drose

(post #106223, reply #36 of 39)

Another defect present in some shop grade is less than fully adhered plys.
That you have to be careful of if using it for form work.

One good way to start down the road to a blow out is using "blow" plywood to start with .


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(post #106223, reply #5 of 39)

Use what you would use for sheathing or subflooring, then after stripping the forms, reuse the plywood for the rest of the structure.

(post #106223, reply #6 of 39)

More info please.

One time use?
How tall and how thick is the concrete going to be?
Exposed wall or buried?
Foundation? retaining wall?

All these can make a difference in what will work and what would be the best choice.


They can't get your Goat if you don't tell them where it is hidden.

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(post #106223, reply #7 of 39)

Here's mine for starters, just to see what you'd use and how you'd build the forms.


One time use on a home which will need about the same coverage area for it's floors as the complete foundation forms.   Plywood will also be used for exterior wall sheathing, more than enough for forms. 


Exposed 8' foundation, 8" thick, 24'X36'.   2X4 and 2X8 lumber will be used in framing the house, enough for all form work. 

(post #106223, reply #9 of 39)

What I was taught when I started out.

3/4 BBX or BCX. (reuse for sub floor w/ joists 16" O.C.) Oil well with form release oil.
(Or 1 1/8 ply and 24" O.C. joists which will produce a "flatter" wall)

Snap ties 24" O.C. (8 ties to a panel, ties drilled at 1' in from each long edge and at 1',3',5', and 7' top to bottom).

Form clips at top and bottom, 4 to a panel at bottom *, 3 to a panel at top.
(* or screw/nail a 2 x 4 down to the footer instead of clips at the bottom, I prefer this method)

Use precut studs for vertical whalers and plate stock and long tail ties at 1' and 5' locations to stiffen the forms. Add one more plate stock 2 x at top of pour for alignment.


They can't get your Goat if you don't tell them where it is hidden.

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(post #106223, reply #10 of 39)

Forgot to add , have a hose with water supply available to wash the outside of the form off immediately after pour, makes stripping and reusing much easier.


They can't get your Goat if you don't tell them where it is hidden.

Life is Good

(post #106223, reply #11 of 39)

That's a nice refresher course Dovetail.  It's been quite a while since I last did form work of that kind so my memory, which ain't too good to begin with, isn't real sharp on the details.  


The only thing different that I recall is using 1x2or1X3 for the shoe, fastened with cut nails.  Just a cheap way to deal with it, I suppose, because the shoe always got destroyed, pulling it up with a crowbar.

(post #106223, reply #24 of 39)

how would you order your ties for a 12" wall if you are using both vertical and horizontal walers?

(post #106223, reply #25 of 39)

Each full panel takes 8 ties.
Both are readily available here for 3/4 and 1 1/8 ply.
Each full panel takes 4 of each style.

Add some for corner details and steps if needed.


They can't get your Goat if you don't tell them where it is hidden.

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(post #106223, reply #27 of 39)

are you saying 8 ties for a 4x8 plywood sheet? I'm sure I would use a few more. never had a blowout and I like it that way


my question was what size tie for a 12 inch wall with vert and horz walers

(post #106223, reply #28 of 39)

Only blowout I was ever involved with happened some 30 years ago when I was a young carp. GC was building his own house and skimped on the ties, lost a 50" wall , we poured the slab before the walls.

For a double whaler system using 2 x 4 for bracing stock then a 12 x 8 1/4 tie.

Ties choice and tail length also depend on the clip being used and whether or not you want to add scaffolding.

Here are the local suppliers snap tie options I have available.

http://masco.net/web/index.php?option=com_content&task=view&id=90&Itemid=60


They can't get your Goat if you don't tell them where it is hidden.

Life is Good

(post #106223, reply #29 of 39)

Here, they're referred to as long-tail and short-tail.  IIRC, that's on the box.  Studs and walers require long-tail ties, 3½" longer tail on each side for the additional 2x4s. 


I prefer to only use walers (no studs), therefore short-tail.  12" short-tail for that wall.   


What are they called where you work?  Gotta be readily available.


Dovetail, do you only use 8 ties/sheet on thick walls? 


PAHS works. Bury it.

PAHS works.  Bury it.

(post #106223, reply #30 of 39)

NO.

The number of ties depends on wall thickness primarily , but also on what I think the amount of vibration, speed of pour, slump etc. of the wall will be.

Using higher grade plywood gives one a bit more leeway as well. The grade of the inner ply can determine how much the ply bows out between whalers just as much as the face grade can.

There are specs that are readily available ( IIRC they used to be printed right on the boxes of ties) that list how many ties and the spacing for different thickness and height walls.

My original answer as to number of holes and whaler arrangement was predicated on what the question was (single use, maximize re-use of lumber on the one project).
To maximize the re-use of lumber for the building I would have used vertical whalers as in wall building.

Generally I ran my whalers horizontal as you do and use verticals for the strong backs. Often bought bunks of 16'/18' stock , used them for whalers then after stripping and cleaning walked them over to the 16" Comet radial arm saw and made precut studs (8' or 9' walls) out of them.

I was doing a lot of high wall foundations back then and so having extra whaler stock , ties or forms was never an issue, just used them up on the next job or took them home and built my 3 story barn out of them. (or chicken shed, wood shed, hog barn etc)


They can't get your Goat if you don't tell them where it is hidden.

Life is Good

(post #106223, reply #31 of 39)

Whew.  That was a relief. 


I learned forming from a book, took me through load calcs.  I assume my ties are doing all the work.   


Which is why I was confident of what I was doing, without any experience.  Had a couple of guys here helping who were certain that my forms wouldn't hold.  They did.  Considerably less lumber on the outside than they understood.


Got a lot of poor advice when I started out, including "never vibrate"- from the readymix salesman who assured me that I'd lose snapties if the vibrator ever touched one.  Didn't happen.  Tested that on my very first pour.


I've used strongbacks, when I got long-tails for a song at auction.  Otherwise, I'm getting flat enough with short-tails to keep me (and clients) happy.


Don't remember ever seeing a box of ties with spacing info.  But my manual's dog-eared.  Helps to know what one doesn't know.


PAHS works. Bury it.

PAHS works.  Bury it.

(post #106223, reply #32 of 39)

I got to thinking about the info being on the snap tie carton. I think what I posted is wrong, there is information on the "Rapid-Form" clips cartons concerning the # to be used, not on the snap tie cartons.


They can't get your Goat if you don't tell them where it is hidden.

Life is Good

(post #106223, reply #33 of 39)

Tom and Dovetail,


I'd like to have a good form work reference in my library.  What book(s) can you recommend? 


Seems like a funny question, after many years of building forms, but I was always a  wage earner on union jobs, seldom saw a print, never an engineer's tables.  I may know what works but I don't know all the whys of tall pours. 

(post #106223, reply #34 of 39)

You will have to ask Tom for the name of his.

All of my knowledge was gleaned out of what I could find to read along the way in the form of suppliers literature, places like this, articles in various magazines etc. and from talking to those who had been there and done it.

I have never had a book that dealt with concrete as the major subject matter.


They can't get your Goat if you don't tell them where it is hidden.

Life is Good

(post #106223, reply #37 of 39)

Unlike Dovetail, I learned my formwork/concrete almost solely from books, then had at it.  Got conflicting advice and decided I'd go with what was printed.


Two primarily: "Construction Manual: Concrete Formwork" ISBN 0-910460-03-5, and "Cast-in-Place Walls" booklet from the American Concrete Institute in Detroit (no ISBN #).


Temperature and placement rate are also covered in the book.  Not that I could control either. 


PAHS works. Bury it.

PAHS works.  Bury it.

(post #106223, reply #38 of 39)

Thanks Tom,  Searching for the first title on Amazon brought up several other books on the subject as well.