These concrete ribs were designed to give me more of an open space feeling without needing to build a wide and tall vault. For more about the design of the ribs or how I made the forms, you can read this earlier post.
This was really an epic part of the earth sheltered home build project, spanning (no pun intended) much more time than I would have liked. The costs for the forms and concrete were pretty minimal, the majority of the cost was actually in hiring the crane to move them around and set them up.
Side note: since I am so far behind… I will probably go and improve the section on the timeline next. Thanks to those of you who wrote to inquire if I died. Nope, just really busy and didn’t have time to put a video together. Speaking of which…
The Video
Lessons learned
The Pump truck did not make things easier. Pump trucks are expensive and I needed it to come out for the floors anyway, so the first few rib pours needed to be coordinated with other jobs. This complicated the planning and made the pour days harder. It also slowed down the progress on the ribs by delaying the pours. And after all that extra planning and delay and expense, it was just plain harder to fill the ribs from the pipe than from the chute because it was really difficult to move it around. I guess my advice here would be to talk to the concrete guys and ask them how they would recommend you handle it. It was probably obvious to everyone except me.
Originally, I used silicone caulk to seal the bottom edges of the forms against the floor. However, this was a pain to clean up later. For the 2nd set, we used play-dough that my wife got cheap on clearance somewhere. The play-dough came up easily enough at the end, but it was such a pain to roll out and put into place that we ended up going back to the silicone for the later ribs.
The first set of ribs took about 4 hours per side to polish. I would start with a diamond cup wheel and then follow up with successive polishing pads at 50, 100, and 200 grit. I also used a special wheel to put a 3/4 inch round on the edges. For the second half of the ribs, I got a larger, more aggressive diamond cup wheel. It worked so well for the first step, that I quickly did all the other ribs. It was only when I got to the 50 grit pads that I noticed the diamond cup wheel had made deeper scratches than the previous one and it was much more difficult to remove them. I even went back to try the less aggressive cup wheel once I realize that the 50 grit was not working well. Overall, this mistake cost me several extra hours for each rib.
The moving dollies were supposed to be able to handle 1000lbs each, but that was clearly an exaggeration. I used more than 10 for each 5000 lb rib and still we had crunching sounds as their ball bearings exploded out all over the floor. The tires on some of them shredded completely. Eventually, I learned that most of the damage happened as each wheel rotated into the correct position to roll forward. By the time I got to the 3rd set, I had learned to point the wheels all in the right direction before lowering the rib on to them. This increased the survival rate considerably. I also salvaged partially damaged dollies by consolidating the less damaged castor wheels on to other dollies.
The rubber form liner molds were an interesting part of the build for me and I like the final look on the ribs, but again, not the best idea. More details below.
Liquid Rubber Form Liners
Originally, I planned to use the Styrofoam ceiling tiles directly, but after handling them a bit, I was worried that they were too fragile and wouldn’t last thru multiple uses. I also thought it would be a bit tricky to place them in the form so they would be centered because they were a bit narrower than ideal. However, if I used the ceiling tiles to form durable rubber form liners, I could get longer pieces that would be reusable and would be the inverse of the tiles. I could carefully center them on a board of the right width so the full depth forms could be easily placed, etc. I did some math to find the volume that I would need and found that I could get the PolyTek 75-75 ingredients for about 175$. That seemed reasonable enough to me at the time. The box of foam tiles was about $40. However, I soon discovered that mixing carefully was critical. My first few attempts were mostly good, but 95% isn’t good enough to cast concrete with. I only ended up with enough decent panels to do a small section of the first few ribs.
For the living room ribs, I decided to make the panels a little thicker (these were the ones I showed in the video). I would need to order more liquid rubber. This time, it was more like 225$, so I was in for roughly $400 worth of liquid rubber. That would have been enough to buy new Styrofoam tiles each time, so not the smartest move in hind sight.
I didn’t quite use up all my liquid rubber ingredients on the panels because I decided to try the Styrofoam ceiling tiles directly on each alternate rib. This way the pattern inverts, positive/negative for each rib.
Cost and timing
See the other page about costs for the forms, but they were just a few hundred dollars and were reused for all the ribs. So divided by 11 ribs, that is just about 30$ each.
The rebar was fairly affordable also. We used about 60$ worth of #5 and about 50$ worth of stirrups, so about 110$ per rib. There were also some steel plates that I built into the ribs and I think I paid about 10$ each for those from the scrap yard. Tie wire and welding costs are hard to guesstimate, but lets say it is less than 5$ per rib.
The concrete was about 1.3 yards per rib, which would be less than $185, even after some waste (Concrete costs about $100 per yard, delivered, but there are a couple other charges).
The molds and ceiling tiles were about 450$ total, so about 40$ each.
Then I bought about 20 of those little moving dollies and some other miscellaneous stuff for about 220$ total, so 20$/rib to move them out of the garage.
The grinder and all the pads were under 220$, but I still have the grinder many of the pads, so I am just going to leave that stuff out.
So lets say the total was $400 per rib. Not bad considering the quote to have it done by someone else was about $8,000 each.
Unfortunately, the crane and welding the ribs to the ring just about doubled that cost. The guys from RTC were great to work with and I appreciated their help, but I had not budgeted enough in that area.
Timing varied as I got better at each task, but here is the rough break down in man hours.
Form prep took about 2 hours per rib and includes cleaning the form segments, fixing any damage, re-assembling the form and attaching it to the floor, and then caulking the bottom edge.
Rebar was next and was taking about 8 hours on average, including getting all the rebar in, tying and welding.
After the rebar was in, I needed to call for an inspection, which didn’t take much time, but did delay the next step.
Next was the pour. It actually took less than half an hour to pour each pair of ribs, but then we would spend at least an hour or so troweling and finishing it off. Lets be generous and say 2 hours per rib. Then there was some delay (several days to a week) as we let the concrete cure.
Then we would spend about 6 hours (3 hours each) unpacking and moving the ribs out of the way. This included a lot of clean up.
And then the cycle could repeat.
After the ribs were out of the garage, I could polish them. The first half took about 4 hours per side to polish, so 8 hours per rib. But, thanks to an overly aggressive cup wheel and adverse weather conditions (hose freezing, etc), the second set took about twice that long. Lets put in an average of 12 hours per rib.
The flip and setup time wasn’t too bad, but lets write it down as an hour each there.
This brings the total hours per rib to about 28. I had 11 ribs to make, so about 308 hours total. If I had done those in 40 hour work weeks, it would have been nearly 8 weeks of constant work (yes, some of those hours or days were worked by other people like Sherri, Bonnie, Aaron, Dan, John and Mark). However, I already had a full time job, and also had other things to work on at the house, so I ended up spreading this part of the build over a whole year. The video on this article covers from July 2015 thru April 2016.
Needless to say, I am glad the ribs are all done.
Gallery
After a long and difficult project, looking over the pics feels pretty good.
To illustrate how you get tangential arcs, important here because the load paths are smooth and in compression
3D model showing the ribs and curved steel I beams.
Model showing the kitchen, I included it here so you could see where the kitchen door slides into the rib.
Euclidean geometry can be built with nothing but a string and nails…
At the corners, it is best to overlap the rebar like this so that neither side can be pulled thru
Ryan and Carter helping with the hose
Moving those 5000lb ribs tended to wreck a portion of the wheels on each cart. Rather than toss out the whole carts, I would consolidate the good wheels together so some of the carts could be used again.
Polishing
First rib lifted up… I tiled the image so the rib would look upright
At one end, the rebar is welded to a steel plate and this still plate gets welded to the steel compression ring when we set it up.
On cold days like this, I placed a heater in the middle and also covered with rigid insulation before leaving for the night.
More finishing
Love this pic of Michael playing on Ribs 7 and 8 while we are finishing up prep for 9 and 10.
More rebar…
Work often runs me past sunset, especially in the winter.
Ribs 7 and 8, ready to pour.
We used a wet grinder to polish the concrete. It had various different cups and polishing pads.
Rebar was fun, the first time, but got old fast. In these joint areas, it got a little messy
#5 rebar along the spine with #3 rebar stirrups to tie it all together.
Some times I welded in extra bars just to keep everything oriented and spaced correctly.
Ribs, forms removed and ready to lift.
The boys playing with balancing against concrete paving stones we made
Polishing the ribs as a snow storm rolled in
Another snowy day… It was above freezing, so I still polished, I just had to get the ice out of the hose first.
Sherri and I were pretty happy after curving the last of the #5 rebar… Just a few more hours of rebar tying left on the last rib.
Sherri’s father (Mark) came out to help pour the last rib.
By this 11th rib, Sherri and I pretty much know what we are doing.
Sherri pulling down the last bits of concrete from the chute
Finishing up the last rib and knowing I wouldn’t need to reset it felt pretty good.
This bottom end of the rib was broken off when the strap slipped and it was dropped. You can see the yellow target that I pained to help guide the crane in. There was also a #5 rebar peg grouted in the middle of the square.
The crane company said I should label this pic as “Mike, the RTC oompa loompa”. All good guys to work with.
We used these bolts to attach the steel brackets to the ribs
The steel attached to the concrete
The view from below after the ribs were setup. This is our “open concept” living room…
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.
Its a short one this week, and the end is rather abrupt, but here it is anyway…
Why a Quonset hut?
My house design is an experiment with a variety of different arch forms. Since it is a self build, I kept most of my spans shorter than 15 ft. The exception is the garage. I wanted a 3 car garage for practical purposes and decided to use a Quonset hut to form the wider span.
The quonset hut could probably support a significant earth load, if it were carefully distributed, etc. But in my design, it is really just fancy formwork to hold up the rebar and shotcrete that will actually support the earth.
My build also required a workshop to build the other components, and the Quonset hut is something that could be erected quickly, early in the construction, and provide that place. I have used it to weld steel arches, store materials, and most importantly, to form my large concrete ribs.
Why build it in two stages?
The rib forms needed to be built on a large flat surface, out of the weather. But we would also need to use a crane to move them to where they needed to go. The ribs weigh 5000 lbs each, so I couldn’t roll them out across the gravel or dirt. Instead, I needed to keep them on the slab, but also needed open sky above them for the crane.
The solution was to build only 2/3rds of the Quonset hut on the slab floor. I could use that sheltered space at the back to form the ribs. I would then jack them up and pull them forward to the open 3rd where a crane could lift them up and over to where they needed to go.
When the crane came out, it did lift them straight up and over, but I noticed that it actually had a telescoping arm. I asked the operator and he said that he could lift them up and pull them out of the building if I finished it…
The ribs were taking me a long time to make and closing off the building would save me a lot of hassle, so that seemed like a good idea. It had been almost a year since the first 2/3rds were erected.
The final 3rd
My parents came down to visit and to pick up their camper. Anyway, it was windy and we didn’t want to try erecting Quonset sections with just the three of us. However, that is a good number for assembling the steel arches, so we spent most of the afternoon doing that.
The following week, I put out help requests on Facebook and at work. The first few days, I was worried that I wouldn’t have at least 4 people there at one single time. By the end of the week there were lots of people volunteering and I was buying a few extra half inch sockets and wrenches so there would be tools for everyone. One co-worker even volunteered his whole family of very capable teens.
The steel ribs went up very quickly. 7 in under two hours. We were actually done before the Pizza lunch I ordered arrived. No worries, we had other work to do (not captured on film).
Mistakes
Because these new steel arch sections were were bolted to the rest of the Quonset hut, which was already bolted and concreted to the slab, and because they were very heavy, I wasn’t too worried about the new section blowing away. With 13 people working in parallel to bolt the sections together, I didn’t want to interrupt that flow and make everyone stand around while I drilled and bolted the steel sections down. I figured I would come back and take care of the anchor bolts next time…
However, by the next time I went out there, I found that the wind had lifted the front third of the Quonset out of the groove. We ended up wasting several man hours and a lot of sweat getting it back into place.
I should have known better because this is a pretty typical fluid dynamics problem that I had to do several times at school.
Another “mistake” that I pretty much accepted was that my building was a little longer than it should have been and ended up hanging over the edge by a few inches. I ended up cutting that off so it wouldn’t get in the way of the end wall, but that is another story.
