I plan to put up 8' walls with 4" core.   The guy I plan to rent the braces from says I should use a loose slurry of concrete to make it go down easy.  According to him I won't even need a vibrator if I do that.  Engineer says no you don't want to do that and that I definitely need a vibrator.   Both the engineer and inspector have to sign off on the structure when they see it completely up and ready.    If the whole structure is up and ready and I don't use a loose slurry how am I going to get it to go in all the way?  How will I be able to check and how will I know?  Will the vibrator fit that far down in a 4" core wall?    Also they say to install vertical rebar after the wall is up.  Let's say I use the PVC ring method.  How am I going to see the rings from way up high and hit my mark and insert them?   In these kinds of cases do you lift the ICF's up temporarily to install rebar, pour concrete in, insert the vibrator?    Can you even lift the ICF's once the horizontal rebar is in place?

I would not use a 4" wall for anything. Most ICF manufacturers don't even make 4" forms anymore. Spend the extra few cents and make a 6" wall. You're asking for voids and rebar too close to the surface to be effective.

Can you even lift the ICF's once the horizontal rebar is in place?

No, you can't.

Does code require you to use the PVC ring method? If the horizontal bars are staggered in the web, the verticals should slip right down the center easy enough. 8' isn't that high.

If the whole structure is up and ready and I don't use a loose slurry how am I going to get it to go in all the way?

You have to watch, very carefully as it goes in and don't put it in too fast. If you lose focus and aren't sure about an area, that is the time to vibrate.....carefully.

I use 4" for my main floors and they aren't a problem at all. They use 50% less concrete than the 6" and the strength is many times strength of any frame construction. For sure you should be using at least a 6 slump and 10m is a better rock size. Using a plasticizer is certainly an option.

As for locating the rebar from the foundation, you can get them close, or to cross each other, by bending the rebar somewhat sideways within the web in your first row of 4". Since you will use the same vertical spacing for the main floor as for the foundation, they should cross each other. Plan B could be to put a "L" bend in the rebar coming out of the foundation to achieve the same effect. The rebar won't be same as using the PVC rings but I don't believe it should be required.

Jack- there is no choice as to whether to vibrate or not. Always vibrate even if you have a high slump it's about removing trapped air and proper consolidation. Some of the guys who've been around for a while ( or not ) might not like the thought of vibrating there block if it's an older generation or whatever. All of the mainstream blocks must be designed to take it because it mandatory.

The PVC trick is a good one but not in the code nor required. The code you are referring to is the ACI 318 -- Non contact splice which states that the bar at the base of the wall must be 1/5 lap length or less from the vertical bar. If you are using number 4 your lap length is usually 40 diameters or 20 inches. All you have to do is lay out your slab bars so they come up more or less in the center of the cell. The vertical will need to be no less than 4" away from the bar coming out of the slab.

All-Saska - some cool ideas there too. Thanks

P.S. All that said I too prefer 6" for a number of reasons.

OK so what I understand is as follows.

The vertical rebar needs to be within 4" away from the bar coming out of the slab. It doesn't have to be tied to the bar coming out of the slab.

Always use a vibrator, because it removes trapped air and consolidates.

One cannot lift ICF's once the horizontal rebar is in place.

I have to watch as the concrete pours into the ICF to make sure it goes all the way down. I am assuming that one can see 8' down into a 4" core ICF wall.

Be aware that some vertical ICF forms will allow the EPS to be moved up during concrete placement so that concrete can be introduced at a lower level.  But since you are talking about horizontal ICF blocks, then the most that I have heard about is that some installers have cut neat holes in the eps side wall to avoid dropping concrete so far.  The removed round piece of EPS can be used to plug the hole after concrete has been placed below that level.  I also hear that it is better to use screws and and some type of board to keep the replaced piece of EPS in place.

My experience has been that it is very difficult for the hose operator to see if the concrete is going all the way down.  Using a person to look into the forms and a person to use an internal vibrator should be enough to assure proper placement and consolidation.  But when it is all said and done, the simplest way is to use a strong mix with a high slump even if it means that an mid-range water reducing admixture must be added to the concrete mix.

The hole in the wall (literally) is an interesting idea.    How far away from each other should the holes be spaced?

I'm putting up a small house, 800 sq. ft.  21.5' x 36'.   So I'm also kicking around the idea of setting up the full 8' wall for the architect and inspector.   Tearing down the top half 4'.   Pouring the bottom half 4' first.   Setting up and pouring the top half 4' later.   The only problem is that I then have to prepare other projects like sidewalk, stairs, etc. to use up concrete for two barrel trucks full of concrete.    The 800 sq. ft. walls at 4" core will use up exactly 10 cubic yards = one barrel truck of concrete.   So two separate pours = 20 cubic yards do not fit my concrete needs.   Short loads?  No problem, there's a short load service in town.  They charge $15/cubic yard more than barrel trucks.   When I tell them where the ranch is located (40 minutes out of town) they tell me to get lost no can do.

Don't forget that you're going to lose nearly a yard in the pump truck.

To keep with the original question: The engineer needs to stick to what he knows best; that is, design. Leave the placing and producing to those who know it. Make the flowable mix (loose slurry) that way with additives, though, not water, such as what Alton suggested. The inspector should just be interested in the finished product.