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As we are in the process of designing and building a house using an ICF I was interested in talking with an ICF homeowner.
A few days ago we had such an opportunity. The general gist of the visit was that the owners were very pleased overall; however, there was one glitch that I would like to pass on.
During the pour the concrete was pumped in and the hose end was kept at the top of the forms. This meant that the mix had to drop up to 8 feet. In spite of vibrating efforts and care in placement hidden problems remained behind.
During the first heavy rain water seeped in between the footings and the bottom of the ICF walls. Investigation revealed that the concrete had separated and not filled the ICF cavity completely. A quick caulking and patch job solved the water seepage problem, but one has to wonder about the stuctural integrity of the entire pour.
We were always taught by our union old timers to never let concrete drop more than 4 feet to its placement area in order to avoid separation. I strongly suspect that this had much to do with the lack of integrity of the walls in question.
For what it’s worth,
Cliff. Johnston
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Cliff, More information is needed to discuss this problem. What type of form was used? Straight wall, waffle wall or post and beam? What was the batch design of the concrete? Mixes with larger aggregate are more susceptible to segregation. We routinely pour walls in excess of 10' in height. With the proper batch design and pouring technic you will not have segregation of the mix.
*We did a home using Rastra and were told to pour at 5' heights max. Our engineer at the time was working on a winery that had the problem you discussed and they had to practically rebuild a new structure around the first. For those inexperienced in icfs, a strict height limit should be kept. Icf specialists, such as Norman above me, may have mastered larger pours. However, the shorter pours were safer, less risk of blowouts and plenty enough work for the day for us anyway!
*Teo, I could not agree with more. The biggest problem in the ICF industry is that people think it is easy and anyone can do it. If you told the average home owner they could frame a house by themselves most would be smart enough to decline. But show them an ICF that stacks like Leggo Blocks and they think they can do it. There are so many variables and problems that can arise when placing concrete it is best left to people with experience. We have some great success stories with DIY's. They were the ones that were willing to pay a little extra for Tech support. They did not attempt to place concrete on their own.
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Well, it wasn't my intention to disparage any manufacturer by name and in print, but seeing as you asked...it was Polysteel's ICF. I understand that the concrete batch was a pea gravel mix.
Surprisingly, to me, the contractor is a reputable guy who has used this product for some time and builds upscale custom houses. I would think that he would have his techniques down cold; however, it just goes to show you - don't believe everything that you hear and only half of what you see.
You are right about the design of the ICF being important. Having seen and heard of this situation and having compared many ICF's I would definately favor forms producing solid straight concrete walls with minimal web constrictions. As one who worked his way through school as a union finisher (more than a few decades ago) - it's not as easy as stacking Leggo's. Even things as seemingly simple as placing and vibrating concrete have their own set of skills that need to be mastered. I shudder when I watch some of the cement crews pouring now-a-days.
*I had no intention to mention any name brands in my initial discussion; however, since you asked...it was Polysteel's ICF. The batch was pea gravel. The contractor is a reputable custom upscale home builder whom I would have thought to have been experienced enough to have avoided this type of problem.Having looked at ICF's for the past 2 years before narrowing down my choices to only 2 there are several factors that have played a prominant part in my decisions. Simplicity and ease of use are important; however, as an old former union finisher I looked carefully at the manufacturers' technical manuals. Whenever I saw a caution against using a vibrator I noticed a high correlation with a lack of a locking/keying feature in the blocks. It stands to reason that if an ICF block can't withstand light vibrating then there is very likely a much higher possibility of blowouts occuring - and who needs a blowout during a pour? Another key feature for me was the design of the internal webs in the ICFs. Some obviously provide formidable barriers to the flow of concrete during a pour. If the webbing is a potential barrier then it follows to reason that obtaining a uniformly sound structural pour with a crew that is not reasonably skilled is going to be very difficult, to say the least. The example that I saw and heard about this past weekend is a good (?) example. I shudder just about everytime that I pass even a flat pour now-a-days and watch mostly poorly trained crews murder the mud. Even seemingly simple tasks such as placing concrete and vibrating it have their own sets of skills that are mostly overlooked today. It's a shame too, because properly designed and placed concrete can be a thing of real design beauty and lasting value. Take a look at most of the pours that have been down a year or two now and you will very likely see expansion and/or settling cracks, ponding after rainfalls, spalling finishes, etc., etc.. It's enough to make one wonder.
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What do you do about the cold joint in the ICF wall at the 5' level when you stop the pour there and continue the next day. Do you just assume that cold joints are not a problem with ICFs?
*We did not worry about the cold joint. I am not an ICF expert, or even much of an amateur, but in this job it was not an issue with the engineer. This being a two-story job, we ended up with 3 cold joints, or four I guess when you count the footing. This was Rastra, with a minimum of #4 @ 15" OC vertical and horizontal and that seems to be enough to overcome a cold joint issue. We were careful not to stop a pour at the mid point of a cell, that is, we tried to keep the joints at the mid-point between any two horizontal bars.And, frankly, with the exception of pouring the concrete, the stuff really is simple to work with. I had a crew of non-builders and building a frame house would have been much more difficult. Another reason it worked well is that we had no power, so the walls were built with handsaws, levels, a rebar-bender and lots of glue!
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As we are in the process of designing and building a house using an ICF I was interested in talking with an ICF homeowner.
A few days ago we had such an opportunity. The general gist of the visit was that the owners were very pleased overall; however, there was one glitch that I would like to pass on.
During the pour the concrete was pumped in and the hose end was kept at the top of the forms. This meant that the mix had to drop up to 8 feet. In spite of vibrating efforts and care in placement hidden problems remained behind.
During the first heavy rain water seeped in between the footings and the bottom of the ICF walls. Investigation revealed that the concrete had separated and not filled the ICF cavity completely. A quick caulking and patch job solved the water seepage problem, but one has to wonder about the stuctural integrity of the entire pour.
We were always taught by our union old timers to never let concrete drop more than 4 feet to its placement area in order to avoid separation. I strongly suspect that this had much to do with the lack of integrity of the walls in question.
For what it's worth,
Cliff. Johnston