You might want to post this over at greenbuildingtalk.com on the ICF forum..

I built my house out of concrete (DIY formwork and I poured the concrete myself with a helper).

I closed off the bottom of the window bucks. I don't have foam on the inside so I can see the cured concrete. It flowed under the buck and completely filled it up. It would have spilled out without the whole bottom buck.

With ICF, I would leave 20% of the bottom buck open (in the middle) in case there's a problem with trapped air or the concrete doesn't flow all the way.

Thanks for the advice re greenbuildingtalk.com, I have now posted there as well.

There are allot of experts there, you'll get great advice.

I lined my forms with 2X2's at the bottom of the windows, leaving about a 3" opening, but still having embedded wood to brace the foam and leaving something to attach to for finish work. I put a few cross braces over that to keep the opening from bowing out under pressure. If the concrete is the right consistency, it won't keep flowing out. As they vibrated the mix, I troweled off the excess. As soon as they stop vibrating, it stops flowing. Your first 'lift' will probably only be a foot higher than the window bottoms, and as you come around to do the next lift. the first one will be set enough to stay put.

I don't understand you saying you are not using window bucks. What are you using? If there is nothing but concrete and foam, it will be difficult to mount windows. You also have to prevent the foam from flaring outward under pressure when you fill the forms with concrete.

Same over here, I left a 3" opening in my bottom window buck so that we could vibrate/ram-rod the concrete under this space to prevent air gaps. Which watching the flow of the concrete *would* have happened if we hadn't manually worked it under the window opening. We then troweled it smooth and for added measure screwed a board over the opening to ensure the concrete wouldn't force out.

My concrete supplier said that some builders have been watering down the concrete for the ICF pours to the point where yes, it would flow right out of the 3" opening (because they didn't want to vibrate or deal with that opening). So if you have a REALLY wet concrete, then yes it would come out the opening, but no you wouldn't need to worry about the air gaps as much, and if you have rather solid concrete (mine really required the vibration), you want that opening in the buck and no, it wouldn't really flow out of it in subsequent pours.

Thanks for all your replies. Just to let you know the pour went really well. There was no flow over the windows so the mix must have been good. We just took off any excess when the concrete was vibrated and trowelled it flat to the correct level. The system we are using allows the first lift to be poured to first floor level (about 2.4m) so this is why I was worried about the weight of the concrete above possibly pushing out of the windows.

To clear up other points raised in follow up posts, we braced at the sides of the windows to prevent the flare but the system we are using comes with the braces built into the EPS so is very strong and doesn't usually flare. Also with no window bucks the window will be directly attached to the concrete.

Thanks again for all your advice

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