This is the final wrap up on the basics of ICF construction we used on our new off grid home.
In my last post, I shared a ha ha sign “Somewhat Precise Home Builders” which is my tongue in cheek name for the contractor who has built our home, namely Johanna and me.
But the carpenter’s level that I have resting on the very top course (double top plate,10th course, 15 feet up) angled across a corner, tells a different story. That bubble is dead on between the lines. It’s visual proof that if we start level, take our time as we work off that base to finish the top course, we remain level. In a previous post, I conveyed to you just how important the foundation was for everything being built upon it and here’s proof of that. I’ve put the level on top of all sides and on the floor in different locations. If we aren’t dead on level, the bubble is still within the lines. That’s as good as I can possibly hope to get.
I also mentioned in my post on foundations that by measuring my diagonals from corner to corner, I could tell if my building was square. There’s another trick I should have mentioned that can help square corners. That’s the 3,4,5 rule. You can learn about it here (http://www.aconcordcarpenter.com/the-3-4-5-method-for-squaring-corners.html) but it’s basic trigonometry. Measure 3 units down one side, measure 4 units down another side and then the distance between those two points (the hypotenuse) should equal 5 units. That works with multiples of 3,4,5 as well, such as 6,8,10 for example. To prove that, take a framing square and with a tape measure, measure the distance between the 6 inch mark on the tongue and the 8 inch mark on the body. The distance will be 10 inches. This method is far more accurate than trying to square up a corner with a framing square.
Working With Concrete
In regards to concrete, I’ve pointed out the importance of wearing eye protection when working with concrete due to its potential to splatter and how I wash thoroughly all concrete residue from my exposed skin as soon as I’m done working with the stuff. I should mention the importance of washing off all equipment as soon as I’m done too. Leaving concrete on tools and shovels for cleaning the next day makes for some tough, if not impossible cleaning.
We needed the pumper truck to fill our ICF walls and that process can be sloppy. It was hard not to slop some concrete about as we worked along the walls, walking on planks supported by staging as we went. Some of that splatter will go on the braces. It’s a lot easier to wipe things down and get that fresh concrete off while it’s still goo. Once it sets, it’s a bear to remove. I know because on our first pour, I didn’t realize the braces were splattered until I took the braces off a couple days later. Then it literally took us a couple of days hacking, banging and scraping to clean off the set concrete. It was much easier this second pour since I knew how to deal with it. Simply wipe things down right after the pour is done and clean up is so much easier.
One important detail in regards to pouring concrete is to remove air pockets and voids in the wall. They obviously would be weak areas and must be avoided. Although one could take a long piece of rebar and tamp the concrete all the way around as it’s poured, the best way is to buy or rent a small concrete vibrator made just for the purpose. It doesn’t take much to vibrate the concrete down. A couple thrusts down and then we moved on to the next spot. We essentially vibrated between every form web to make sure we were filling the entire wall with a uniform layer of concrete. A word of caution. The pro we had helping us made certain not to over vibrate an area. This can stress that area and cause a blowout or bulge if one is not careful, especially in the corners which are the weakest areas.
I’ve given quite a bit of detail on what ICF is and how we utilized it. I’ve also mentioned that the concrete is reinforced with rebar. Every course has horizontal 10M rebar. There are a number of slots in the plastic webbing to accept the rebar. The rebar snaps into place. Each successive course of horizontal rebar alternates position so that it forms a cradle for the vertical rebar that needs to go in. In other words, if you looked down inside the wall, a piece of vertical rebar placed in the wall would be sandwiched between alternating layers of horizontal rebar, thus keeping it in place vertically. All horizontal rebar was overlapped a minimum of 24 inches when I needed to start a new piece. I’m just giving you some of the basics since local building codes and ICF manufacturers will dictate the proper rebar spacing and sizes needed.
I did a tremendous amount of rebar cutting. In hindsight, I should have spent the money on a rebar cutter/bender right from the start and then sold it if I had no further use for it. It would have saved an enormous amount of time and effort. For the most part, I used a diamond cutting blade in my circular saw to cut the rebar. Towards the end, I was able to borrow a cutter and it made short work of snapping pieces in two.
In every corner, I had a 60 inch piece of rebar bent evenly into a 90 degree angle with a smooth radius. I was able to bend that by hand. What I did was take a 60 inch piece of rebar, put it on a flat surface, then laid a 3 inch heavy steel pipe on the midpoint. By stepping on the pipe with my weight, I could reach down to the end of the rebar and simply bend the rebar around the pipe until I had a 90 degree corner. That worked well and was pretty easy.
Form Lock and Joint Clips
There were also some additional supplies we bought from the Nudura ICF dealer that made our structure better. John at Bird Stairs Ltd highly recommended Form Lock and Joint Clips when he was quoting our project. I’m glad we listened to his advice. The form lock is a reinforcing steel web that goes in on various courses. It’s purpose is to help hold the wall in a straight alignment. In our case, we put the form lock on the 2nd, 5th and top course all the way around the perimeter of the building.
We used the joint clips on the corners to draw the joints tight. Tight joints keep all the dimensions very close to the same all the way up as each course is laid. Joint clips were also put on each seam on the first course at both the top and bottom of each joint. This is to lock all the butted seams together. Because I had lots of extra clips, I used them on the very top course on every seam too.
It was recommended that we do our pour in 2 stages since the total height of our walls exceeded the brace capability. It could have been done in one pour but we would have had to do some creative bracing for the entire height of the wall which was 15 feet. Although doing the walls in 2 pours was the safest option, I found that as I continued to build the walls higher in preparation for the second pour, my blocks didn’t align as cleanly after the first pour. I had a couple of sections I really had to wrestle with to get together. Once I got them locked together, I fortified the joint by putting on a clip.
One other thing in regards to doing multiple pours. Prior to the first pour, we taped plastic over the very top course of ICF interlocking nubbins to prevent concrete from splattering and filling in all the voids. A tedious process, but if we didn’t protect the top course, concrete would surely have filled some of those voids making it impossible to build the next course until the concrete was removed. It would have been a disaster really. So at all costs, the interlocking nubbins had to be protected. We salvaged the plastic material that the ICF forms were wrapped in and thus used the recycled plastic for protection. It worked well.
One problem we encountered was after we did the first pour and then built the forms for the next pour, we had effectively created a water well. The concrete is purposely left uneven on the first pour to create more surface area for the next batch of concrete to adhere to. But that also leaves plenty of pockets to accumulate rain water. Although the concrete will displace a lot of that water, I didn’t want to run a science experiment to prove that point. So I rigged up an extension pipe on my wet/dry vac hose and sucked countless gallons of water out of the wall just before we did the second pour.
So although this was never meant to be instructions for building your own ICF home, I hope I’ve given you some good information on what is involved with ICF construction. Although building with ICF is quite easy, there are many considerations and techniques that must be mastered in order to do a proper job.
I’ll tackle more individual topics at a future date such as our roof trusses and flooring system as well as how we finished the exterior of our wall before we back filled with dirt. Please stop back for my next post which will tackle refrigerators and freezers for the off grid home.
Until next time, keep the dream alive! We wish you a great day!
Ron and Johanna
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