ICF blocks seemed like the perfect solution for the front of my garage where they would be needed as walls for the garage and as a parapet to hold back earth over the roof, without needing any special handling for insulation. There have already been previous posts about my Fox Blocks training and my early work with these. Now that I am all done with installing my ICF blocks, this post includes FAQs about my lessons learned, costs, etc., but first, the video
Video
Earlier Post
There was an earlier post about why I chose Fox Blocks, the training, etc. The rest of this post will be about lessons learned since then.
FAQs
Why pour in a series of small pours?
The more concrete you pour at a time, the more pressure is exerted on the forms and the more concrete will come spilling out if anything goes wrong. In other words, I wanted to take baby steps.
I also couldn’t pour the front wall at the same time as the back wall because I needed to leave the front open while I continued to make those big concrete ribs in the garage.
I couldn’t wait on the back wall because I needed to mount the electrical service somewhere and the pump truck was cheaper than it would be to start on a temporary structure and then move the meter.
Even brave people are limited by the physics (hydrodynamics) of pouring concrete, so I did pour the front wall in only 2 stages instead of 3. But even with my growing experience and confidence, I didn’t sleep well the night before we did that pour over the garage door openings.
Why Scaffold Jacks on the north side, but regular scaffolding on the south side? Why not ladders?
When you are building the ICF walls, I guess you could use ladders. It would be a hassle to keep moving them around, but it would be possible. However, when it comes time to pour the wall, you need to be able to move swiftly along the top of the wall. You can not keep stopping the pump truck to climb down and move the ladder . You need some sort of working platform.
The north wall was poured in stages over a long period of time because I was waiting for times when I had the concrete pump truck coming for other reasons (such as the basement floor or the quad deck floor). During that time, I knew I would want my scaffolds for other tasks, such as setting up the steel framework. Home made scaffold jacks were the easy and affordable solution because I could just leave them in place and move them up as needed.
By the time I got to the north wall, I was just paying for the pump truck and doing my pours much closer together, and I wasn’t using the scaffolding for other tasks. I also didn’t think the jacks would have worked well across the open garage doors anyway, and the driveway was nice and flat for stand alone scaffolding… So I just used my regular scaffolding.
How much did it cost?
I bought the Fox blocks at Menards, so you can check their website for the prices, but they were just under 20$ per block (16 x 48 x 12 inches). The walls then got filled with concrete that cost about $100 per cubic yard (27 cubic feet). There were also some clips and a bunch of wood (I used a lot of scrap from earlier projects), rebar that I already had laying around, etc. I buy the rebar by the ton, and pay something like 35 cents per ft. If I do some fun math, and divide things out per square ft…
Fox Blocks = 3.75/sqft
Concrete (6 inches thick) = $1.85/sqft
Rebar = 0.35 cents.
—————
Total = $5.95/sqft,
Plus a few cents for clips, etc. That is not too bad for a 12 inch thick wall, but it is about double what it would cost to frame a 2×4 wall with 4 inches of insulation and house wrap. I didn’t have separate steps to attach vapor barrier, insulation, etc. because those are all built in, but clearly, I still spent a lot of time putting up patches, etc.
I don’t regret going with the ICFs because I think they are much better in this application as parapet (retaining wall) for the dirt on my roof. The concrete wall will be much stronger and much longer lasting without any risk of rot, etc. There is also the dynamic R value of the concrete in the wall that will keep my garage much more thermally comfortable. My wife likes that no insects or mice will get thru it, but in the mean time, some birds are trying to make nests in the exposed polystyrene.
What I left out of the above calculation, because it is a real kicker for me, is renting the pump truck each time. Filling a 14.5 ft tall wall without a pump truck isn’t really a practical option. For the first two sections, we scheduled the wall pours to align with the basement and quad deck floors, so no additional cost there. However, for the other two times, we just had to pay for them to come out for just a tiny section of wall… Each pump truck visit was about 700$, which is more than the cost of the concrete we pumped. Each pump truck also required me to order a couple extra cubic yards of concrete just to fill the hose (that all gets dumped out at the end). If we were doing a larger chunk of the house in one go (such as a whole house built of ICF blocks), we could have improved that ratio a lot.
How about time?
Yes, I did this work over about 6 months. Mostly that was to align pour days with other tasks that would need the pump truck. I was also working full time and basically only building on Saturdays and some weekday evenings. The actual time spent stacking blocks was not too bad. How would it compare with stick frame? Probably similar. Certainly it will last longer.
What was with all those edge patches?
There are no attachment points on the ends of the fox blocks. They attach to each other, end to end, with clips between the plastic webs. The styrofoam just buts up against the other blocks, so it has some compressive strength, but no tensile strength for holding screws. When you attach the end bucks, etc. you need to connect to the high density polyethylene furring strips built into the front and backs of the blocks. To do this, I screwed boards (like 2×6 boards or sheets of particle board with 2×4 blocks) to the front and back of the ICF blocks and then I could screw the end boards to the sides of these.
I am pretty sure all the vertical end walls and especially the ones for the top of the garage door opening were critical for containing the concrete. The patches, such as the one along the vertical seam shown in the video, were also critical.
On the top edge of the wall, I had cut a sloping shape. When we poured in the concrete, if it was too wet (high slump), it may have simply poured out the sides again. I knew there would be some pressure on these sides, even if it was not as great as the vertical sides, and I wanted to contain and shape that concrete. The concrete did push at the top/side forms for the first 3 pours, but for the last pour, the slump was so low that the concrete probably would have just sat there in the shape of that hill and let me trowel it smooth. In that last case, the boards were just in the way and made it difficult to get the concrete down inside where it needed to be.
Tips:
1) The best tool to cut the ICG blocks with was a battery powered jig saw with the longest blade you could buy.
2) Get a concrete vibrator. Harbor Freight has a cheap one. It makes a huge difference to the flow of the concrete, which means you can get lower slump concrete (which sets up stronger) and still have it nicely flow around all the rebar and ICF webs without any voids.
Before buying the vibrator, I had wondered if it would be worth the money. Professional grade vibrators cost hundreds more. As it was, I thought it was a great little investment that got me thru all my ribs and my walls and died 5 minutes before the end. I haven’t needed it since, so I haven’t tried to fix it yet. Maybe just a switch died?
3) Because the ICF blocks look like lego, any many of us “do it yourself” builders were lego maniacs, we some times assume that overlapping the blocks (running bond) is important. When something in the wall makes this difficult, we might want to waste lots of time or chop up expensive blocks trying to prevent a vertical seam. But it is totally unnecessary. Unlike bricks (masonry or lego), the little styrofoam nubs on the ICF blocks do not actually hold the wall together in the long run. The void gets filed with a monolithic concrete pour that ignores all those stacking details. Instead, just focus on making sure the surface of the wall is patched so the forms won’t split open along the vertical seam.
Gallery
Just some related pics.
Continuing over the Door Buck
The boys can’t resist the camera
An accidentally pic as we moved the go pro
Aaron out on pour day
Ryan checking out the camera
Aaron and Simon handling it
Sherri troweling off the wall
2×12 buck for the exhaust fan
On the North wall, before trimming it. This platform is 14 ft off the ground.
North wall after trimming. It was supposed to be filled along with that floor.
Pouring the wall with Ryan
By this point, I was pretty comfortable with the concrete hose.
Here Ryan is climbing up the ladder to help me by vibrating the concrete. He doesn’t like heights, so I appreciated his bravery.
Full bracing
After removing the scaffolding, bracing and patches.
Starting work on the round window buck
I stacked these blocks, numbered them, drew and cut my circle hole and then took the wall apart so I could put it up where it belongs.
Sherri messing around for the camera
After getting in the window buck… Felt pretty good.
Night shot, I appreciated the lights on the short January days. It looks like a scene from an underwater exploration movie.
The south wall, before trimming.
Picking up the camera at the end of the night, looking tired.
Inside the Fox blocks wall, there are black HDPE plastic brackets to hold the rebar, etc. The blocks are “clipped” together with wire clips.
Sherri and Michael posing on the last pour day.
After the pour.
After removing the scaffolding and most of the patches.
As part of my build, I wanted to experiment with a variety of different construction methods, including ICFs.
ICFs are “Insulated Concrete Forms” that you can use to build a very well insulated wall. They stack like lego and include strong high density plastic (HDPE) inner supports that hold the sides together while the concrete is being poured. This inner web structure is also used to position and support the rebar and the portion embedded in the polystyrene acts as furring strips for attaching things to the wall. After the concrete is poured, the forms are just left “in place” as insulation.
In addition to the 4 inches of polystyrene insulation, we will be adding 6 inches of concrete that will give the wall mass to retain heat, “dynamic R value“.
The front and back of my garage (Quonset hut) are flat walls that needed to extend past the Quonset hut and perform double duty as a parapet retaining wall, all without any complicated construction or difficulty attaching insulation. ICFs seemed like the perfect choice for this application.
The final setup
Installing the Fox Blocks ICFs was pretty easy, as you can see in the video. Lessons learned are included in this post.
The Video:
Fox Blocks;
I looked at many different ICF companies and carefully considered their various advantages. Some fold flat for easy shipping, others have longer or taller blocks or come in separate pieces that can be assembled in a variety of different ways. Cost of materials and installation were also a concern. In the end, Fox Blocks was my first choice. For more on why, see this earlier post.
The blocks cost about 20$ each and I was able to buy them directly and install them myself without any fancy tools or equipment (or skills). A regular concrete block wall (CMUs) would have been cheaper, but would have been much more work and required much more skill. I would also have needed to insulate it, so maybe not even that much cheaper.
The Story (lessons learned in orange boxes):
The Setup;
We started out by measuring and marking all the locations for doors and windows right on the concrete pad/footing. From this, we could easily mark all the locations for the rebar. We drilled half inch holes 3 inches into the concrete at each rebar location.
The Fox Blocks stack very easily. We also use the “Fox Clips” to clip the blocks together horizontally and vertically. After each layer, we added the horizontal rebar. My engineer specified one piece of #4 alternating near the front or back of the wall each 16 inches. The internal web of the Fox Blocks had notches to hold the rebar so that we didn’t even need to tie it in place.
The lego bits (that Bonnie insists are called “nubbins”) are every 2 inches and the blocks can be stacked upside down or back to front, but you definitely want to line up the internal webs so that it is easy to clip things together vertically. It also makes it easier to attach things to the outside of the wall if the webs are all lined up.
In the first section of wall, we had a T section for 3 levels on the back. So when Bonnie got to the 4th level, it was a bit tricky to trim a block for that transition and you can see her trying a few different things (stacking and unstacking and then trimming and re-stacking) to get all the internal webs to line up.
After the wall was mostly up, we started dropping in the vertical rebar (half inch) and then using a hammer to tap the ends of the rebar into the half inch diameter holes in the footing. These 3 inch deep holes were enough to hold the rebar vertical within the wall, however, in many cases, I still wire-tied the vertical rebar to the top horizontal rebar just to keep it all where it was supposed to be. This vertical rebar strengthens the wall and also helps the later layers hold across the cold joint at the top of this section of the wall.
When initially constructed, the blocks are securely attached to each other, so you have a monolithic form. The vertical rebar keeps it from moving very far in any direction, but it is still very loosely positioned and not plumb. You can see it moving around a lot in the video. The wall will need to be plumbed and aligned as a final step.
We screwed 2x4s into the sides of the bucks. It is very important to screw them in where the plastic reinforcement is. In those locations (which act like internal furring strips), the screws bite in nicely and hold well. Anywhere else, and they will just pull right out of the polystyrene. these strips are hidden under the polystyrene. Fortunately, the blocks are clearly marked with the words “Fox Blocks” along the furring lines.
Unfortuneatly, I was not clear enough when working with my friends/family and assumed they all understood how the plastic strip locations were marked. When their screws would not bite in, I would say something helpful like, “You need to make sure you screw it into the FOX BLOCKS.” and I would point to the line that said “FOX BLOCKS” vertically on the side of the block. I would even screw one in for them to show them how it worked. They would nod and smile, but were actually thinking, “Yea, I am screwing it into the Fox Blocks, what did you think I was doing? But its not working for me!”
It also didn’t help that we were (at least initially) using screws that were not threaded far enough up the shaft. It was fine for the 2x4s, but when used with the thinner boards, the threads passed all the way thru the plastic and spun without really tightening up. This caused quite a bit of frustration for Zack who was in charge of putting up the thinner boards.
Once the 2x4s were in place, we positioned and plumbed the ends of the walls using bracing and stakes to fix them in place. Then we stretched string between the ends so we could align the rest of the wall. Section by section, we used a level to plumb the wall and the string to align it. The bracing at each section was individually staked.
This turned out pretty well, but I didn’t factor in potential movement at the bottom of the wall. I had not fixed all the degrees of freedom and had relied on friction and the weight of the wall to keep the base where it was. Of course, an ICF wall is relatively light and the strong winds shifted it in the 2 days between setting it up and the concrete pour. I ended up needing to make some last minute adjustments. Next time, I would also do something to secure the location of the back of the wall along the bottom edge.
Holes for the windows are cut out of the Fox blocks. We used “Fox Bucks” to frame around the windows. Fox Bucks are similar to the Fox Blocks (Polystyrene molded around an internal webing of tough HDPE plastic), but without the “snap together” feature. Instead, they must be taped into place and then the seams are held together with externally applied boards screwed in on both sides (the block and the buck). Again, it is critical that the screws be in the plastic within the Fox Bucks, but the plastic fills pretty much the full sides, so it is hard to miss.
Not everyone helping understood that the concrete would be exerting hundreds of lbs of lateral force to push the bucks out and that tape and a couple screws would not hold them. I understood, but my big mistake was not fully inspecting (I was too distracted) that the boards were screwed into both the bucks and the adjacent Fox Blocks every 8 inches or so. This lead to some blow outs and additional work down the line. More images of this sort of mistake in the gallery at the end of this post.
The Fox Bucks are also used at the top and bottoms of the windows. When used as window sills, we had to cut holes to allow the concrete to be poured in. We also sloped the sills (by trimming the front of the underlying blocks) so water would drain off.
The full height of the wall is 12 blocks tall, but we only setup the first 4 levels because we wanted to be sure that the concrete would consolidate all the way down in the forms. If we were more experienced, we may have tackled a deeper pour and got more done at once. But as it was, I was glad we kept this first one simple. Stopping at 4 levels also meant that I could let the first part harden before I added concrete across the tops of the windows and garage door, which probably saved me a disaster. The cold joint that will occur is bridged by the vertical rebar.
The final steps were to place 6 mil plastic to separate the coming concrete from the Quonset hut steel and to spray foam some gaps and along the bottom of the wall. It not only fills gaps to keep the concrete from leaking, but works as a very effective glue.
The ICF wall was inspected and approved. Keep in mind that the inspector checks basic things like if you have Rebar in place, etc. He does not check for every screw. As the general contractor, that was supposed to be my job.
The Pour;
On the day of the pour, we also planned to take care of the basement floor and the concrete ribs while we had a pump truck on site. I was actually running on fewer than 4 hours sleep and still frantically finishing some final details on the rib forms when the concrete trucks were rolling up. I should have been inspecting the forms. Is that enough foreshadowing for you?
Since I had experienced concrete guys on site to take care of the floor, I also asked them to help with the ICF walls also. To make sure that the concrete was properly consolidated in the walls (without air pockets, etc.) I had bought a 5 ft long concrete vibrator for $99.00, which I would recommend to anyone doing similar work.
As soon as the concrete started filling the forms, the end started popping open. It was immediately obvious that one of my helpers (who shall remain nameless) had not really understood that concrete would be trying to push its way out of these forms and had not secured things nearly enough. For instance, on the first end, he had only fastened the top and bottom of the board. Hundreds of lbs of lateral force were pushing out the middle and we had to scramble to brace it. The windows bucks held up well, but then one side of the garage gave out and a few hundred lbs of concrete spilled out while we frantically grabbed scrap wood to brace it. Seeing that not nearly enough screws had been used, I ran ahead of the concrete hose and frantically added more to the other bucks.
We made sure that the forms were not filled all the way to the top and we roughed up the top surface of the concrete so that the next layer would grip well across the cold joint.
It all happened very quickly… So quickly that, for the time-lapse, I had to slow it down by 50% so I could fit two sentences into the scene.
Once the day was done, I had time to think about my mistake and plan to do it better next time. There will actually be several more phases and I will need to wait until all the rib forms are done before I can complete the garage and put another ICF wall on the front of it.
Gallery:
Here are some pics from the day with descriptions. Thanks to all those who helped me out.
The Fox blocks arrived in light weight bundles of 12.
Approved
Dimensions on the computer model
The final setup
Michael playing tag (caught by the time-lapse cam)
Zack and David working together.
Here I am wire tying the vertical rebar to the horizontal
Bonnie trimming off the end
The Fox Blocks are light weight and easy to handle
We also put in a little side wall for the Mud room
No screws holding in the Fox buck at all…
Here you can see why the middle bulged out. It would have blown, but we braced it in time.
David inspecting the damage
Clips hold the blocks together
Here you can see “FOX BLOCKS” written vertically, aligned with the internal plastic
