I have a concrete formwork job coming up. It’s a small commercial building with a parking lot. I haven’t seen the prints, but I’m told it’s jam packed with radiuses. Does anyone have any tips for radius formwork, shortcuts, trade tricks, asymmetrical layout techniques, etc..?
Edited 11/6/2005 9:36 pm ET by JourneymanCarpenterT
Replies
segmented radius you can use 12" forms ( 1x4,1x5, 1x8 , etc. )
for true radius you have to make up your forms with the largest ply thickness you can bend to the radius.. typically 3/8" say... two layers of 3/8, break the joints
btw.... are the radius in the building . or the parking lot ?
I don't have that information yet.
Edited 11/18/2005 6:48 pm ET by JourneymanCarpenterT
I would talk to a commercial concrete supply house. They sell forms and all sorts of other stuff that commercial concrete guys use. Somehow I started getting a couple of monthly rags in the mail that cater to the commercial concrete scene, and I can see from the ads that there are tons of really trick things out there for forming all sorts of stuff. If you're near a big city you should have at least one such supplier at hand.
Us residential guys, we make forms out of wood... definitely the hard way to do it for something like your project.
OK, a quick Google got me this.
http://www.gatesconcreteforms.com/
Sounds familiar. Where?
PAHS Designer/Builder- Bury it!
Have you done any radius forms before or is this new ground. Basically I want to know how famililar you are with their construction. So I may know what you need to know without getting into writing a book.
I have done a fair amount of radius formwork. there are some prefab products out there which may be usefull, but if you need to fab them yourself I will be happy to give some pointers.
some things to consider: you will run your walers vertically ( this was a surprise to someone in a previous thread) don't forget to account for thickness of plywood when laying out your inside and outside plates. you can uses either steel or 2x4 walers depending on wall......
I'm probably telling you stuff you already know.... before I get carried away which is what I started out saying I wasn't going to do...tell me what you do know and how you plan to proceed and I'll fill in the blanks.
for radius , we use than 1/4 inch masonnite type material.
Masonite inside the 3/8 formwork or 2X curved wall?
Smooth finish.
Yes, I have done some radius formwork before. I usually use two layers of 1/4" plywood. In the past if it was a foundation wall, I would use a couple layers of 3/4" plywood for walers. I'd trace them off of templates. If it was for something shorter, I would fasten the 1/4" plywood to metal stakes. I have always made the forms up out of wood, except for Simons forms, and the occasional metal earth forms.
On this job I will have to make the forms from wood. Although I like to use plywood, I've worked for this guy before, and he only provides 2x material. I suppose I could cut kerfs in the 2xs, but what depth, and what intervals are best?
The building is about the size of a big house. It's also a remodel. Last time I worked with the guy, most the radiuses were in the parking lot. This time however, because he has told me there are so many radiuses in the plans, there might also be some in the building itself.
Last time I worked on such a job, most the radiuses weren't a perfect circle, but an ellipse. It was quite a fuss to get them to look right. Any tips or shortcuts on laying such forms out?
Edited 11/8/2005 4:24 pm ET by JourneymanCarpenterT
Edited 11/8/2005 10:09 pm ET by JourneymanCarpenterT
Edited 11/10/2005 9:33 pm ET by JourneymanCarpenterT
Edited 11/18/2005 6:44 pm ET by JourneymanCarpenterT
Circles: Here's some links to some Circle Calculators, including a Circle Center Calculator.
Ellipses: The Foci of an Ellipse can be determined by basic geometry. Or plot the points around the perimeter with this Ellipse Calculator.
These calculators work best using the MSIE browser.
Joe Bartok
Edited 11/8/2005 4:42 pm ET by JoeBartok
Edited 11/8/2005 4:44 pm ET by JoeBartok
Edited 11/8/2005 4:53 pm ET by JoeBartok
Thanks Joe, this ellipse formula should come in handy this week.
Edited 11/18/2005 6:44 pm ET by JourneymanCarpenterT
Last time I worked with the guy, most the radiuses were in the parking lot.
What exactly do you mean by this ?
Radius curb forms ?
Radii drawn on macadam ?
?
carpenter in transition
"in the past if it was a foundation wall, I would use a couple layers of 3/4" plywood for whalers."
If I'm reading that right, you are saying that you custom cut 3/4" ply, doubled it up so that esentially you have a 2x4 radius waler for use with snap ties.
if that is that case....that would be a very slow and wasteful of materials method. ( if not the case then disregard) what you describe is ideal for a top and bottom plate for your form but not for the walers. what I was taught was to cut the top and bottom plate as you described then cut to length 2x4 walers that will run vertically. I believe their was a link by one of the other guys that shows a picture of what this will look like. remember, the tighter your radius the closer together your verts should be. a common spacing might be 12" oc. but if you were really tight one could get even closer.
"On this job I will have to make the forms from wood. Although I like to use plywood, I've worked for this guy before, and he only provides 2x material. "
tell him you want plywood. how are you pricing the job? if he will only supply a material for a job that would be better served by another material it should be reflected in your price.
"I suppose I could cut kerfs in the 2xs, but what depth, and what intervals are best?"
You can. But I hope you are referring to a curb form. If you are talking about having to stack the 2x whatevers to get the height you want, you are looking at alot of work for a poor result. Did I mention, ask for plywood? The only time I have used 2x stock is when forming radius stairs for a pour (aside from a curb or patio) and you will still need plywood radius plates for your stock to conform to.
As for the intervals again it depends on how tight the radius. a gentle radius might be around 3" a tight radius could be around 1 1/2". leave about 3/16" to 1/4" stock in your kerfs, and remember to face the kerks to the inside. if concrete will be exposed then you can face the inside with a smoother material - dare I say plywood...lol. or some other smoother product.
a few things I will add:
It's often easiest to form one side in place, then form the other side in sections, then move the panels into place when you are ready to close up.
if the concrete will not be exposed ei foundation wall that gets burried. you can use quick strip ties with steel waler bars. ( method easiest for buttoning up) the difference is, provide essentially enough 2x4 verticals to nail the plywood joints to. (24" oc) then after you are closed up drill holes to slide the ties through, and holes in the top plate to slide the waler bars down.
when cutting your radius plates. make your template exact. but when you cut your plates you only need to cut the side that will have the form attatched to, a precise cut. what I mean is trace your template on the plywood one above the other, because the inside and outside have a different radius your plates will have different widths along the radius. but that way as you make the inside cut on one radius you can use the offcut as the outside for your next plate instead of making 2 cuts for one plate. I hope you followed that, it cuts your cutting in half as opposed to one who were to make 2 seperate cuts for each plate.
I hope this also answers your question to, timkline.
Last time I worked with for this guy, they were radius curb forms. A lot of the radiuses were also quite tight. This time, however, I vaguely remember him saying there are no radius curbs. This is also something that leads me to believe I might come upon a radius footing, or maybe a foundation wall. My guess is that most the radiuses will be in the parking lot slab itself.
The last time I was on such a project we used 2x4s. I figure this is what will be supplied this time also, especially since you say you use 2x stock for curbs as well as patios. And no, I would never stack 2x's on top each other, even if someone put a gun to my head. Okay, maybe if they put a gun to my head, but only because I value my life.
Unfortunately, it won't do much good for me to ask for plywood. It's a volunteer building project for a non-for-profit organization. They usually don't come upon a lot of radiuses, but when they do, they seem to use what they already have. Further, the foreman overseeing the project doesn't know me very well yet. He also doesn't know much about the trade either. He's a truck driver. It will probably take some time before he takes my suggestions more seriously.
Being a volunteer project, I could bring a sheet of my own plywood. This might be especially helpful if you think it could be used in conjunction with the slab forms.
When you mentioned conforming stock to plywood radius plates, did you mean for radius stairs only, or for curbs and patios as well? I have never used plywood radius plates for curbs or slabs, and would be interested in how this would be done. Usually, I just connect one straight run to another, and then try to make it come out right.
This is the same method I have used for radius foundation walls. I noticed, though, that you described a top and bottom plate for these forms. I think I get the Idea here.
In regards to walers, the only link I noticed was: http://www.gatesconcreteforms.com/pages/24m.htm
What I see are 2x4 uprights backed up by horizontal metal radius walers. This system looks great if have it. It would definitely be faster than cutting the walers out of plywood. I see how it could save on material cost also, since you could use them for many different radiuses. Is this what you are referring to? If you only have wood on the job, is there a different method that cutting horizontal radiuses out of plywood?
Your tips on saw kerfs should come in handy on Saturday. Using plywood templates for foundation walls should also make setting up the radius a lot less of a fuss. Please explain your technique if you also use plywood templates for curb and patio forms. My job foreman (not this volunteer project foreman) has always laid out the radius waler templates. I think he's made them two sided. Either way, Ill be sure to make them two sided if I do it myself. Even if I don't use them for walers (depending of course on how you answer my question). I can definitely see how this would cut some of the work in half.
Any more answers to my questions would be much appreciated.
Edited 11/18/2005 6:43 pm ET by JourneymanCarpenterT
ok...where do I start...I'll just ramble for a bit to start then reread your post and try to answer anything I missed.
1st off I understand your perdiccmant being a volunteer project. That definatetly makes it trickier. If you will only be dealing with curbs, ok I could see you getting away without plywood. (*expetion to follow ) however anything other than a curb form you will have to have the plywood.
as for a radius footing....throw that idea out the window. it does not need to be a radius, you just need a footing that your radius wall for will be able to sit atop. so....use straight lumber and build it octagon style ( for lack of better term) even if your wall ends up not being centred on the footing in all spots that will be fine just get it close enough.
*( for the exception). for most patios or curbs with a radius wether using a bender board or 2x stock usually it is bent to the desired shape and simply staked into posistion. Most of the time this is fine, especially if your form is only 3 1/2". but lets say you needed to go taller and you wanted use say a 2x10 or 2x12. it's often hard to keep the stakes straight and even if the soil allowed you to pound your stakes straight, if a specific radius is called for how are you going to get it? I could go on about the possibilities, but lets just say that it is easier and will give you the desired result to have a radius top and bottom plate fabricated to fasten your form boards to.
I will give one example. I once had to build 2 forms for landings at the top of 2 different exterior stairs. ( This was a yard that we formed radius walls thru out the entire back yard. there were three sets of radius stairs. afterwards it was all faced in granite - we used the steel walers method, since it got covred up.) anyways, 2 of the landings had a radius, the 1st one I did the bend it and stake it method. I got it as nice as possible, but I thought it could have been looked a little better. The next one I decided to cut some radius plates and use that method (since I had plywood I faced it with plywood.)
The 2nd one had a nice perfect radius. I tweaked the 1st one to make it look a little better. But sure enough, the next morning I got a call from my boss; the owner had come home that night and seeing the 2 he wanted the 1st one redone to look like the second one. So I redid it with radius plates and felt much better about about it.
now don't get me wrong there are many times when a nice radius can be achieved without plates, it is done all the time. But if a plan calls for a specific radius or you want to achieve a specific radius then usually you need to layout a specifc radius.
"What I see are 2x4 uprights backed up by horizontal metal radius walers. This system looks great if have it. It would definitely be faster than cutting the walers out of plywood. I see how it could save on material cost also, since you could use them for many different radiuses. Is this what you are referring to? If you only have wood on the job, is there a different method that cutting horizontal radiuses out of plywood"
yes and no...the system I am describing is similar. what they have looks like it is probably a comercial job and they are using a double waler method. They snap ties they use are long enough for the wall plus the verts plus the walers. the double waler method is more common on comercial jobs and for use on taller walls. I once work on a house that had a 20' high foundation and we used the double waler method.
there is also what is called the single waler method. the ties used are long enough for the wall plus one set of walers. This is what you could use. your clamps will be applied against the vertical walers. the radius is acheived by your top and bottom plates.
as for cutting radius plates.I hate to say it but plywood is what you need. If you are forced to use 2x stock use the widest possible stock you can get your hands on. But I cringe just thinking about it. It is one thing to cut a 2x trim radius. but if you are cutting a lot of radius out of say 2x12.here are some of the probelms.
1st of all cutting...what are you going to cut them with a jig saw I guess. when I cut radius in plywood I set my circ saw just a bit deeper then the plywood and cut away. with 2 x stock if you can even make the cut you are going to burn out the blade half way thru the 1st cut. unless you are dealing with maybe a 50' radius.
second: you will have join the plates. I suppose you could just build your wall in sections and cleat the joints being sure to also put your bracing at the joints. as you know when you use plywood you are able to overlap the plywood to make a continuous radius.
third: again unless you are dealing with a pretty large radius you can only get so long a piece cut out of your 2x, which leaves for many joints in your plates. bleh!
"Please explain your technique if you also use plywood templates for curb and patio forms. My job foreman (not this volunteer project foreman) has always laid out the radius waler templates. I think he's made them two sided. Either way, Ill be sure to make them two sided if I do it myself. Even if I don't use them for walers (depending of course on how you answer my question). I can definitely see how this would cut some of the work in half."
I covered the patio/curb part. By two sided do you mean plates for the inside and outside form? abuslutely yes. without the plates your plywwod will have nothing to hold its shape. some guys when they do straight forms will leave out the bottom plate for the inside wall having it held only by the ties and walers, which is fine, but for a curved wall you will want both top and bottom plates on both sides of the form.
I hope you got the part in my last post about tracing and then cutting them. If you are dealing with alot of radiuses that will mean alot of cutting. just remember that when you are cutting plates for the outside form it is the smaller radius that you care about, when you cut the inside plates it is the larger radius that you care about. use your template and trace em out to look like a rain bow. it will have a funny shape to it but that is fine. if you cut all your plates exactly 3 1/2" as your template is you will not be able to lay them out one on top of another. you will be making 2 cuts for every single plate and also wasting the material inbetween each traced out line.
I have to get up early so I'm going to stop there, and also I have said alot. sorry I have made it so long. I hope that this will help you. If you can come across to the truck driver guy formen as confident in what you say maybe ( I hope) he will get you some ply wood somehow. Pls let me know if I have not been clear on anything ot if you have anyother questions and I will do my best. I'll reread your post tomorrow to see if I 've missed anything......
good luck
Thanks a lot, alrightythen. Your experience with radius forms has been very helpful. This Saturday should go a lot smoother than it would have otherwise.
If anyone has any final tips, there always welcome. Otherwise, thanks everyone for your contributions.
Edited 11/18/2005 6:40 pm ET by JourneymanCarpenterT
good luck .....let us know how it went.
I left the volunteer project earlier this evening. It turned out that all 17 radiuses ended up being in the parking lot slab. Fortunately, this time we used flexible metal forms for many of them. When the metal forms ran out however, we resorted to wood. This time, they decided to double up 1x6 material.
Before I got there, I had already had my mind set on cutting kerfs if plywood wasn't available. Unfortunately, I don't know if this was the best idea. Starting on a 20' wide radius, I simply used the wide side of my circular saw plate as a gauge, cutting my way down the board. I left the recommended "1/4 inch stock" remaining in my kerfs. This probably would've worked, but as I set the board kerf-side-in, one of my partners insisted that the board would bend easier if I set it kerf-side-out. I had never done it this way before, and unfortunately again, I let him try his idea. Although this was only the first layer, the board did ended up cracking rather easily.
Needless to say, we wen't back to setting the boards kerf-side-in like I had it. This of course, made the board easier to bend. But it still seemed quite fragile. This was only emphasized when I found out we didn't have screws long enough to screw through the stakes into the forms. We did however have 8d nails. This reduced the stress on the board a little bit. Cracking, though, was nearly inevitable.
Perhaps the 1/4" links would halve worked just fine in 2x material. In 1x6 however, I can say from experience, it's probably not a good idea to cut deeper than 1/2 the thickness of the material. This is what I ended up doing on the next board. On that board I could feel the tension in the 1x6, but the 3/8" links were sufficient to keep it from cracking. Because the boards were kind of flimsy however, it was still kind of a frustrating process.
One guy was quite successful slowly bending the boards with bar and C clamps. He neither wet nor kerfed the boards. He simply applied slow, easy pressure. This worked on radiuses shorter than 20' as well. Oddly enough, this was one of the guys I worked with last time when we used only 2x4s instead of 1x6s. He used the same technique then, with dismal results. He busted several of the 2x4s, one right after another. He ended up convincing the foreman that it could not be done, and bending only part of the radius.
I suppose this might be why I was so intent on using the kerf method. I suppose also, that some of this might seem quite obvious to someone who specializes in concrete formwork. I however, do not. Some days I form, some days I frame, and some days I finish. Some days I work with wood, and some days I work with metal. I suppose that's one of things I like about my job, there will always be more to learn.
As I mentioned before, when I form radiuses, I'm used to always using two layers of 1/4" plywood. I could'nt help but ask the volunteer foreman why plywood was never supplied. His answer was that 'the plywood they make nowadays cracks too easily.' From my experience, I find it hard to except this as fact. In a way I'm glad though that we didn't use plywood. It's nice nice to know what the best techniques are for bending different kinds of material.
All in all, it was an enjoyable day. Both lunch and dinner were served, the people were very nice, and we all had fun working together.
Thanks to slykarma for his input. I found the attachment especially interesting.
Edited 11/14/2005 4:27 pm ET by JourneymanCarpenterT
Edited 11/18/2005 6:36 pm ET by JourneymanCarpenterT
"one of my partners insisted that the board would bend easier if I set it kerf-side-out."
lol...well now he knows - yes it will bend easier but it will also crack easier.
as for 1x6 sometimes you can get away without kerfs but if you do need kerfs about half is a good amount to go with, as you have concluded.
It sounds like the the forman isn't very experienced.... you said he was a truck driver -right? but oh well it is a volunteer project..which is good and you had fun which is good and you learned some new things which is great.
Everyone, here's an interesting link I found to a kerf cutting formula (see box):
http://www.abcsignproducts.com/pdffiles/EASY8.pdf
Edited 11/14/2005 7:24 pm ET by JourneymanCarpenterT
Edited 11/18/2005 6:34 pm ET by JourneymanCarpenterT
This formula posted by ABC Sign Products seems to make sense. It looks likes like they use it mainly for cutting metal, but I think the application can also be made to wood:
http://www.abcsignproducts.com/pdffiles/EASY8.pdf
(Outside Perimeter - Inside Perimeter / Saw Set = Number of Kerfs
Outside Perimeter / Number of Kerfs = Distance Between Kerfs)
Here's an example using doubled up 1x to form a 20' radius:
Outside Perimeter:
20' x 12" = 240" (r)
240" x 2 = 480" (r2)
3.1416 x 480" = 1507.968 (pir2)
Inside Perimeter:
240" - .75 (3/4" thickness of material) = 239.25" (r)
239.25" x 2 = 478.5 (r2)
3.1416 x 678.5 = 1503.2556 (pir2)
Outside Perimeter - Inside Perimeter =
1507.968 - 1503.2556 = 4.7124
/ Saw Set = Number of Kerfs:
4.7124 / .125 (1/8") = 37.6992
or
38 Kerfs
Outside Perimeter / Number of Kerfs = Distance Between Kerfs:
1507.968 / 38 = 39.6833684 (39 11/16")
or
39 3/4" Between Kerfs
If only 1/4 of the perimeter is to formed, the number of kerfs is divided by 4:
37.6992 / 4 = 9.4248
or
9 Kerfs
with
39 3/4" Between Kerfs
A 16' 1x would thus be divided up with 5 kerfs. A 12' would be divided with 4 kerfs. A 10' with 3. An 8' with 2.
This is the second layer. The first layer is as follows:
Outside Perimeter - Inside Perimeter / Saw Set = Number of Kerfs:
1503.2556
- 1498.5432 = 4.7124
/ .125 =
37.6992
or
38 Kerfs
38 / 4 =
9 Kerfs
Outside Perimeter / Number of Kerfs = Distance Between Kerfs:
1503.2556 / 37.6992 = 37.2224238
or
37 1/4" Between Kerfs
The 16' 1x would still be divided with 5 kerfs. A 12' would still be 4 kerfs. A 10' would still be 3. The 8' however, would now also be 3.
Edited 11/18/2005 6:33 pm ET by JourneymanCarpenterT
I was finding it difficult to understand this "vertical waler" concept. After all, how would you hog trough something like that? I did a search and found this informative thread by mike4244:
"(Use)* top and bottom plates out of 3/4" plywood. . . . The plates are doubled, arranged so the joints are spliced. . . . The studs are 12" on center . . . Walers are not needed, the studs are the walers. The studs are nailed flush with the plates you cut."
I think see what's being talked about now.
*Text in parentheses mine.
Edited 11/18/2005 6:30 pm ET by JourneymanCarpenterT
"(Use)* top and bottom plates out of 3/4" plywood. . . . The plates are doubled, arranged so the joints are spliced. . . . The studs are 12" on center . . . Walers are not needed, the studs are the walers. The studs are nailed flush with the plates you cut."
mike explained it well, I'm glad that you get the idea now.
As for the math formula I was intrigued by it as I have nerver seen a formula for kerfs. I noticed it was for metal, so I don't know how relevent it would be for applying to wood, as wood behaves alot differently then metal- but you never know.
....then I saw all the math that you did. woa....lol...I like math but I'm not a math genius. I do like using math for certain applications, But I think for kerfs I kinda go by what looks and feels right. I can always do a small lengh and see if it looks like it will work and adjust if needed.
but still... always good to look at new ideas...
I never want to grow old and become " an old dog that can't learn any new tricks"
excellent reply.
just a terminology question for you.
here in pa, we call the horizontal braces on the backs of the forms walers. in our commercial forming, when vertical bracing is necessary as well, it is installed on top of the walers (same as you, i'm sure) but is called a strongback. have you ever heard this term ?
carpenter in transition
In BC we use that terminology. Walers can be horizontal or vertical. If used, strongbacks are vertical. There is also the older double waler system that uses 2x4 vertical studs with horizontal doubled 2x4 walers and wedges. This is stronger again than single waler system with Burke clamps, but requires three times as much 2x4.Lignum est bonum.
Yes I have heard of strong backs and often use them - when there is a step in a foundation form for example.
You are right about the terminalogy for the uprights in a two waler system, where the horizontals are called the walers and the verticals are called stronbacks. As for the sytem itself, I know it as the "double waler ststem" But I am sure that it has other names as well.
In the "single waler" system in which there is only one set of 2x4's the 2x4's can be horizontal or vertical, and are called "walers" even if they are veritcal.
If you have a radius wall to form then the best system is single waler. This is strong enough for work up to 8 ft high. Both sides of the form are pre-fabbed wall panels using whatever plywood will bend to the required radius. The attachment has a guide to minumum bending radius for common plywood thicknesses.
Like any wall you need studs and plates. In this system the plates are curved; typically they made from a double thickness of 3/4" ply, or ripped directly from 2x material if the radius is very gentle. Studs will be 2x4. The studs will also serve as walers. I know mostly we are used to walers running horizontally, but they work just as well vertically. Ties are standard short-end snap ties (not Strip-EZ) and they are clamped together with Burke clamps. Any decent concrete supplier will sell you the ties and rent you the clamps. You need two per tie.
Make plate templates by swinging an arc directly onto a sheet of plywood. When you make the template, lay out the stud locations on the outside wall form at 16" centres, and then space the inside wall template at the appropriate distance back (wall thickness plus plywood), and mark in the stud positions so that they are radial with the outside wall studs. That way you will have the ties running radially and buttoning up the form will go smoothly.
Ties are on a 16" x 16" layout and the stud layout should be done so that a tie hole is drilled next to each stud. The Burke clamps will attach to the studs.
Using the templates, cut and identify all the plates. Then build the walls and sheet them with ply, using screws for extra pull-out resistance. Now you're ready to stand up the wall panels. Typically footings for such walls are formed segmentally.
Scribe a wall radius for the outside form on the footing and set the first panel on the line. Fasten it down and brace the wall plumb at both ends and centre. Check that the entire wall panel is at the correct radius and adjust if needed. Add another panel and repeat the process. Keep bracing and setting the panels to radius one at a time as you go to keep the forms from 'growing' out of radius.
Then insert ties and wedge them onto the studs with the Burke clamps. Shoot pour height, install any bulkheads or drops required, and set the rebar according to engineer's requirements.
Button up should be fairly quick. Fish each tie into the hole but don't clamp yet. Stand all the form panels up and check that the ties align along radius. Once all the panels are in the right place, clamp all the ties off and cleat the forms together at the top if necessary. Pull a tape along the entire form for a final check of correct radius and you're ready to pour.
Email me if you have questions. I have a curved wall project going on at present, I'll take some photos tomorrow and post them so you can see some of the process.Lignum est bonum.
Sly you use the same method which I have used. The only difference is the outside wall I lay the plates in place and stud up then brace the entire wall, then sheet. then drill. Once that is done the ties and clamps are put in. then in goes the steel etc...
for buttoning up. I do the the panels in segments as you describe.
on some walls that don't have to look as nice one can use quick strip ties with using just enough studs to fasten plywood. Buttoning is is a snap, you just have to drill hole and feed the ties in after. Then drill holes in the top plates and slide the walers down.
Both ways work, but for a nice wall where the concrete will be exposed use the 2x4 waler method with the snap ties and burke clamps.
Here are photos of a curved wall job I'm currently working on. The walls are technically grade beams, because they have no footing. The four concentric walls are to become outdoor amphitheatre seating. People will sit on top of the concrete wall, with their feet resting on compacted sand backfill against the wall in front and below. The walls are 16" thick and 42" high, with the top 18" revealed. Short-end snap ties with Burke clamps placed at 16" centres in both directions. The radii range from 24 ft to 35 ft.
The forms were pre-fabbed so that grading work could be done. Plates are double thickness form ply, stud/waler material is 2 x 4. The forms are sheeted with 3/4" paper-face form ply. The straight run sections have the same construction details.
Additional complexity factors:
architectural concrete: all joints to be caulked, no visible blemishes permitted, all ties to be identically spaced horizontally and vertically.
no pour strip allowed, so forms are built and elevated to exact finished height and poured full. Forms rest on 2x2 grade stakes pounded to exact elevation using laser.
the stiff form ply caused the plates to distort slightly to a larger radius. Turnbuckle braces were used every 4 ft to adjust the form back to correct radius.
all dimensions in metric; bulkhead locations specified only by swept angle from gridline.Lignum est bonum.
All post seem to be good ideas. We often use Masonite lap siding 16' lengths, variety of widths depending on project. 16' length helps in many situations. It can be doubled in thickness if necessary.
A pro concrete supply house here has "benderboard" 3/8" x 6" x 16'-pool guys and driveway guys use it alot. The supply house is Shepler's / Houston, TX.
I've seen sonotubes cut length wise and staked with 2x for tight radii in curbs.
We always form our curved forms with plastic. Check out epicplastics.com. They have 1x4 and 2x4 for about .50 and $1/ft, at least here in CA. We get it at the lumber yard. Mostly used as a landscape edging. Not even a special order. Comes in 20 footers and I know they have x6 as well. When you're done, pressure wash the lumber if you're anal, but either way, it's reusable.