Hi, we are currently building an ICF home and are ready for the first pour.  Please can anyone help with  what may seem like a naive question?  We have braced the windows on three sides but have left the bottom of the window open to pour concrete under the openings to lower the risk of voids.  We were not planning to cover the bottom of the window after the pour.  Will the concrete flow over the window openings as we continue to pour the concrete above?

Thanks

The concrete will not overflow significantly if the slump is correct. Simply put slump is viscosity.
Slump should usually be 5-6.

Most installers abide by the ACI code rule of approximately four feet per hour lifts. Generally, installer will place concrete one foot or higher than the bottom of the window. When installer vibrates the sides of the window from the top and the bottom via opening at bottom this will cause concrete to hydraulic up a bit in the window but not over flow. You want to move on when you have a a foot or more of concrete higher than the bottom on each side so when you come around an hour later the concrete will have set up enough to hold when you add another 4 feet or so to it.

Notice I said when not if installers vibrates. Regards

Good idea to leave the entire bottom of the window open so you can be ensured proper concrete placement and consolidation.

We do the same, however, we have a piece of wood ready to place after concrete is in and completed. If you do not want wood there after pour is complete, make something temporary to install, even waiting an hour the pressures from the next lift can cause the concrete below the window to push and your usually busy watching the rest of the pour that you may forget to hit it down and have some chipping to do after.

I used temporary strips of 7/16" OSB screwed down with drywall screws after we poured and leveled the concrete under the windows. I had the strips pre-cut and ready to install and standing beside each window prior to the pour. It probably took <2 minutes to install each strip. After the pour was complete, the temporary OSB strips were removed.

Thank you all for your really helpful posts.

Arkie6, can I ask a further question? What did you screw the drywall screws into, which part of the structure?

My window bucks are 2x treated lumber ripped down to fit inside the ICF forms. For 6" ICF core walls, I used 2x8 lumber (7-1/4" wide) and ripped it down to 6" wide to fit inside the foam cavity. This wood was used on the top and both sides of the window buck. For the bottom of the window buck, I ripped a treated 2x4 in half and installed both pieces in the the bottom of the window buck leaving a 3" opening in the middle to place the concrete under the window. This is what I screwed the OSB strips to. Also note that I attached the ICF foam to the window bucks using 3-1/2" screws and 2" plastic washer every 8" around the window buck. Door bucks were done similarly except with no bottom.

Once again I'm a little astounded that a dealer or distributor that sold you the forms , can not answer these questions. If you buy the product from them, they should give you assistance. I hope you have someone that has poured an icf there to help you or the worries about concrete pouring out of the bottom of the windows will seem minor. Get help! I disagree with some pros on this site that icf's are not a diy project. My Great Pyrenees "Wilson" can stack blocks if you put peanut butter on them. The pour is a whole different story. When the concrete comes out of the pump, you own it. Hopefully you know that the concrete has to be vibrated to fully consolidate it. I mean a real vibrator 1.75" at least. Every job that I do at 5-6 slump the concrete doesn't even fill under the windows without vibrating thru the sill openings when using a 6" block and rebar.

I can't stress it enough since seeing you original question. Get help!

wow really i have to agree with smartwall, whos blocks are you using, they local dealer may not have all the answers but the block manufacturers always have a technical guy available or they should, tell us the system please!

Sue - since I prefer all my concrete to be encased in foam, after vibrating the window openings, we knock down the concrete 2.25" and insert strips of the block foam. A couple of strips of fibre tape or any other strapping will ensure there is no concrete bulge.

Here are a couple of pictures of my window bucks on my main floor (6" core ICF):






I also remembered that I had some leftover 1" thick EPS foam sheets and I cut pieces of those to fit down in the openings in the bottom of the window bucks before I placed the OSB strips over the bottom.  The wood strips in the bottom of the window buck provide convenient attachment points for windows or additional window framing inside the buck that may be needed with a mid mount window arrangement.

good pics, looks like you are using Quadlock but the foam is the wrong color, nice window bucks, do you plan on using windows without the mounting flanges?

or i guess i am asking is how are you mounting windows to that wood buck? do you have pics of that also, would like to see that too.

The ICF in my photos is LiteForm Xtra. Windows are mounted, but I don't have any photos showing the detail. The windows on the back (south side) are mounted in the middle of the wall. I made the window bucks 6"wider and 4.5" taller than needed for the window. I then came back and lined the inside of the window bucks with 2x6 lumber (a single SPF 2x6 on top, double SPF 2x6 on each side to create room for a brick pocket, and a double treated 2x6 on the bottom to create room for a sloped concrete sill). As each 2x6 was installed, I laid down a bead of expanding foam before the 2x6 was placed and screwed down. These 2x6s are flush with the inside edge of my ICF foam for drywall attachment. The outside edge of the 2x6s are in the middle of the ICF wall. I then installed 1" thickness Type IX (2# density) EPS foam over the outside edge of these 2x6s and caulked and sealed all edges. Then the windows were installed with their 1-1/4" nailing flanges nailed through the 1" foam into the underlying 2x6s. It was a lot of work, but I like the finished product. If I wasn't using a brick exterior that turns into the window openings, then I could have just made the window bucks 3" wider and 3" taller and lined the inside of the bucks with a single 2x to attach the window nailing flanges. I have a few windows on the front (north side )of the house that are mounted flush with the exterior and this is how they were installed using 2x4s inside the window bucks.