I'm going to build a small house using ICF's.  The architect prescribed 4" core blocks.  I have heard all kinds of nightmare stories about how the vibrators can't get into the blocks that size.  The architect prescribed #4 rebar every 2 feet horizontally and every 14 inches vertically.  Near a door he wants me to use #5 every 6 inches.   Do any of you have positive or negative experiences with vibrators using 4" core blocks?   I would like to hear your stories/remedies/warnings/suggestions. 

Go with a high range water reducer and a 5000lb mix it should flow with very little problem. You redi-mix co can replace some of the aggregate with more course sand. It should really give you super flow. Place your rebar on the rebar fingers closest to the interior wall leave the outside open for vibration. The only thing that I do differently, is I add Helix fiber to my mix and skip most of the rebar.

Also use a block that has a small web profile like a Fox block and also a block that has a 8" on center web and smooth interior. The less crap inside the block the better.

You could try Polycrete Flex850. 1' x 8' knock-down block. It has a 4mm steel wire cross ties and a 2' horizontal polymer fastening strip. No plastic web taking up space. (Sorry Ren)

Posted By smartwall on 12 Mar 2011 01:23 PM
Also use a block that has a small web profile like a Fox block and also a block that has a 8" on center web and smooth interior. The less crap inside the block the better.

I like 8" O.C. webs for a number of reasons, and agree - especially for commerical - the less clutter in the all the better.    However, smooth interior is not better, vetical groves - either dove tail or square prevent horizontal water movement should water somehow get into the wall.  Regards.

It also retards the flow of concrete . When you deal with 4", smooth and less restrictive webs is the way to go.

We are going to have to agree to disagree. If you have proper slump and are vibrating properly you won't have a problem. I wouldn't compromise and have a smooth interior wall to avoid a little vibration. I would add however, if you desire to remove the foam later for some reason -- e.g. elevator shaft then smooth is better. Regards.

Did you ever wonder why the newer block designs have a smooth interior and the older designs are grooved.

As far as I know, the only reason many manfucturers are making a smooth-faced interior on their forms is because it is easier (ie, cheaper) to manufacture.

A notched interior (especially dove-tailed) gives the concrete something to bond to. Concrete will shrink as it cures - with a smooth-faced interior, that concrete can pull away from the foam, causing a channel that allows vapour movement between the EPS and the concrete. This is a small channel, but I know of one house personally that had excessive moisture problems around windows, from moisture build-up in this space (at least that was the engineers' final opinion).

When I pour a 4" block, I am sure to use a 1/4" pea gravel as aggregate and I always use a 1" diameter internal vibrator with no issues. Also, very important to only use contact splices when installing rebar as this will allow concrete to flow more easily and will minimize interference with the vibrator.

So if I follow you the concrete pulls back from the valleys in a fluted interior but not from the ridges. Interesting.

The concrete in an 8" wall is going to shrink by about 1/16". If there's a "lock" on the interior face of the EPS, then the foam will tend to stay in contact with the concrete. The EPS does not bond to the concrete, nor do Polypropylene cross ties (a/k/a Webs). The 4mm steel wire mesh that is embedded in the EPS panel on Polycrete Big Block has a loop of 4mm steel wire at each cross tie that extends into the concrete. Not only does the steel cross tie bond to the concrete, but the loop of 4mm steel wire acts as a lock, holding the EPS foam in contact with the concrete.

Having said that, I have been excoriated by some posters on this site for mentioning improvements that our product has brought to the ICF industry. The entire point of this forum should be to reflect the advances in a much maligned and misunderstood industry. I offer solutions to problems. Not rumors, opinions, misinformation or myths.