After a lot of setup work, we were finally ready to have the shotcrete sprayed over our bedroom wing. The Quonset garage was actually done at the same time, but that is another post.
In this post, we have some pics to illustrate the process and challenges, along with some tips for anyone planning to do something similar.
But first, The video.
The Video
Challenges
Financial
Try to get a quote that includes some expectation of how far they will get.
With each shotcrete visit, the cost (when I divide out per yard) has gone up dramatically. I don’t have the calculation right in front of me, but this visit was more than double the cost per yard of the basement job, and that first one totally blew the original estimate out of the water. So, as you can imagine, we have now (writing after the 3rd shotcrete session) blown thru all the money we allocated for shotcrete in the budget. It is not so much that the shotcrete company underestimated the daily costs, but they dramatically overstated the amount they could get done in a day. During this run, there was one day when they only got 8 yards (because the compressor broke), other days got 16 or 24. They said they would pro-rate, but in the end, the costs were all the same per day. If you are paying a daily rate and the volume can vary from 8 to 24 yards, it is difficult to budget.
We will need to come to a better agreement that factors in some of my expectations when we do the next shotcrete. We want to be fair (it is hard specialized work), but we don’t want to go bankrupt either. Next time, I am going to try and work in some better expectations of how far they should get for the money. It probably seems basic, but I am sure it is easier said than done.
A few more guys is a good thing.
Each day costs thousands of dollars for the base crew and concrete… The extra finishing guys are just a few hundred dollars each. That is a bargain when you realize how much energy they save the base crew (so those guys get more concrete up) and how much smoother they make the walls (so you can save on waterproofing).
The lift will save you more than it costs.
The lift rental was over a thousand dollars. This got worse because the shotcrete took a weekend and several days more than expected. But actually, they guys at Wolverine Rental were pretty cool about it and made me a good deal that factored in days when I wasn’t actually using the rental, even though it was sitting on my lot.
The crew would have liked a nicer lift with a more powerful engine and tracks, I can’t even comment on how much more that would have cost because I simply couldn’t find one at any of the rental places in my area. I suppose it would have saved a little time (they got stuck a few times), but probably not enough to justify the additional cost (I am guessing it would be a lot more).
The crew also complained about not having a second lift for the finishing crew. Looking back, this may have paid for its self… I’ll have to do a more careful financial analysis when I get a chance, but probably. Looking forward toward my remaining shotcrete jobs, I don’t think there will be enough lift work to justify two, but maybe…
After saying all the negative stuff first for some reason… I will also say that I am pretty sure the lift really saved us more than it cost. Certainly, it was necessary for reaching the awkward hard-to-reach places with that shotcrete hose. But it also helped in the other areas where they could have used scaffolding or some “cheaper” method. It helped move the hose around and allowed the guys to conserve their energy so they could get further in a day and do a better job. I can do a quick mental calculation and say that it easily saved me much more than it cost.
Update: Funny side update, but 6 months later the Shotcrete contractor texted me to say that the lift (which his crew operated) damaged his 900$ hose while it was pulling it around. Later in the text conversation, he said he would be nice and not bill me for the damage. ¯\_(ツ)_/¯
Chunks
One of the mix trucks must have had some old cement set inside it after a previous delivery. When it brought us our concrete, those chunks broke off and jammed up the concrete pump causing us to lose nearly an hour while the shotcrete guys tried to get the chunks out again. Because we delayed the cement truck past the time they expected it to stay on site, the concrete company charged us an extra fee (75$), which was nothing compared to the value of the delay to us… Any longer and we would have had to dump the remaining concrete. At the time, Sherri took this picture of the chunks so we could argue against the silly charge, but in the end, the 75$ wasn’t enough to bother fighting.
The chunks of concrete that came out of the mix truck and jammed the concrete pump. Sherri’s shoes for scale.
Equipment
The concrete comes from the supplier in a mix truck. The factory adds the dry ingredients into the truck according to the recipe from the shotcrete guys. It is basically a 7 sack mix with sand and peastone and Fly Ash (carbon nanospheres that help it flow) and various other admixtures determined by the weather and other conditions. Along the way, water is added and the barrel of the truck turns to mix it up while on the way (which is why it is called “transit mix”). They need to get the concrete out of the mix truck and on the wall within 90 minutes of starting to mix it.
Once on site, the concrete truck dumps the wet concrete into the hopper of the concrete pump. This pump uses a 110 HP Cummins diesel engine to power two large 6-inch diameter pistons that can handle pumping concrete with aggregates at a rate of up to 50 cubic yards per hour. Of course, they never got above 8 yards per hour, but that is more a function of the complexity of my design.
Meanwhile, the compressor sends high-pressure air thru the smaller hose (1-inch diameter) to the nozzle where it meets the pumped concrete and blasts it thru the nozzle and out into the air…
All of this comes together in the nozzle. The most obvious control is a mixing valve for adjusting the ratio of air to concrete right behind the nozzle. The concrete pump is controlled by a remote that was usually carried by another guy (who could go over and check the pump when something goes wrong). The nozzle man indirectly controls the flow rate of the concrete pump by communicating with hand signals (and occasional verbal abuse) to the guy with the remote. The nozzle is also pretty heavy and the video clips show how the nozzle man has to work with his whole body to control it, often while standing in very precarious positions. The end of the nozzle is a rubber tip that can be switched out depending on the task or concrete properties. The nozzleman can control the fan of the shotcrete spray by pinching this tip with his fingers.
From there, it is all muscle and skill as the nozzleman builds up the concrete in the right places, properly encasing the rebar and all the other annoying things I have in my walls.
These are the main pieces of equipment that make shotcrete possible.
Big job
Shotcrete requires a lot of setup to get rolling. Once the guys get rolling, they can only put up so much concrete in any one place before it starts to schlep off. Instead of doing the bedrooms and Quonset separately as two smaller jobs, we combined them. I am pretty sure this saved us money and gave the shotcrete guys somewhere to go when the one-half of the project needed some time to cure.
Gallery
I guess I’ll tell the other stories here in the gallery.
Bonnie helped me get a lot of final prep work done, like sweeping off the footings and adding extra ties (not sure how overboard we went).
First shotcrete
Nothing is getting thru the screen
First wall
First troweling
second wall
Troweling the walls
Starting on the next section while the guys trowel the first
Three guys each doing their part
At one point on the first morning, it started it rain. Bonnie and I put up plastic to keep it from causing problems on the inside shotcrete. Actually, at this point, Bonnie is doing all the work and I was just taking a picture
These are the main pieces of equipment that make shocrete possible.
Part way thru…
Getting started
Shooting an internal wall while I setup the camera.
If the house didn’t need to be buried, this “transparent” roof would be really cool.
Scaffold jacks are faster to place than scaffolding. They just cut a hole in the shotcrete to make a ledge for one side. Later, they patch up that hole.
Scaffold jacks are faster to place than scaffolding. They just cut a hole in the shotcrete to make a ledge for one side. Later, they patch up that hole.
Early on the first day
This east end gave the most trouble for the shotcrete, but they got it eventually
For some reason the color of this pic really pops…
Occasionally, to get the right angle, they had to get out of the basket. But they minimized this for several reasons.
The lift was really essential for this job. In addition to making it possible to reach the high places, it also took a lot of load off the crew by helping to lug around the hose.
The chunks of concrete that came out of the mix truck and jammed the concrete pump. Sherri’s shoes for scale.
While they were there, I had them pump in a couple footings bits that I forgot to include earlier.
Shooting from the lift
This part of the wall was too high to reach from the ground and too awkward to reach from the roof, so it just didn’t get troweled. Here is where that second lift would have come in handy. Instead, it was a nightmare to waterproof… More on that next time.
At some point part way thru…
Smoothing out the inside surface after they guys are done shooting… It is easy now. Much harder after everything sets.
Smoothing out the inside surface after they guys are done shooting… It is easy now. Much harder after everything sets.
This is how most of the inside surface looked. The screen effectively blocked the shotcrete from blowing thru the lath.
This is how the inside surface looked when there was a gap in the screen.
David just sitting in the hall at the end of the day… Seemed someone picturesque in a war-zone kind of way.
I loved going up in the lift to get a good view (and pictures) of the project.
Low angle lift view
The boys, up in a lift, looking over the work.
IN the afternoons, after the crew would leave, Sherri and I would use the lift to do other jobs, like put up lath on the garage.
This is a couple days in.
Here you can see some of the insulation we stuffed in the valleys to keep the weight down. We then covered over this with additional concrete so water could easily flow off.
3rd day, working on both the garage while the bedrooms were curing.
Here you can see the rebar, vent stack, etc. near the top of the quonset hut.
This was two or three days in…
Guys on the roof of the Quonset on the last day.
Top of the quonset
At the end of the second to last day, the Quonset hut was rough and the skylight curbs were not quite finished.
Final view of the garage from the lift.
The master bedroom has windows facing south and east
The master bedroom ceiling had a somewhat “fabric” look to it when it was all over.
Inside the master bedroom, this back corner will become the master bath.
Sherri is very concerned about upsetting the neighbors, so she was out there trying to sweep off the mess after all the trucks left.
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.
There are several stories in the works. I am waiting on the septic field to be completed so I can tell that story. I am also waiting on the inspectors opinion of my waterproofing tests. The latest drama is my inspectors concern about the back-filling. Since this concern came in after the footings were formed, it could be quite costly to remedy… I’ll find out tomorrow where that will go (it ended up fine, video of the back-filling showed enough tamping). In the mean time, I am guessing I won’t get any more permits approved until we sort these things out.
So, lets talk about something completely different, my new Over the Tire Tracks (OTT) for my Skid Steer.
My skid-steer was pretty useless in sand. As soon as you start to turn, it starts to sink and and you are quickly stuck. I researched over the tire tracks (OTT) and quickly discovered that even if you buy tracks, they won’t work very well unless you also buy new tires. The back tires were already new, I just needed to replace the front tires… I figured that I should replace the tires and see if I still needed the tracks. $400 later, I discovered that my skid-steer was still pretty useless in the sand.
I don’t spend money lightly, and OTT are expensive, so I spent weeks looking for a decent “used” pair. Occasionally, the steel bar kind would show up on Craig’s list. Of course they were all rusty and most seemed to be for the wrong tire size or spacing… but the kicker was that they were still selling for more than half their new price. From my research, I knew that these bar tracks would give good traction on some types of ground, but I needed “flotation” on the sand. I needed wide rubber pad tracks. I didn’t see those second hand anywhere.
Also, OTT tracks also require at least 3 inches of space between the tires and the side of the Skid Steer… I measured and had only 2.25 inches. I called around and found that the 3 inches was definitely a minimum. The solution was to buy and install “wheel spacers”, another $300. This made me wait even longer to order…
Eventually, I gave in and ordered a set of Prowler Stealth OTT with the extra spacers. I almost backed out, so the sales guy offered me an even better deal, plus free shipping. They arrived a week later on a 1400 lb pallet that I was able to easily offload from the truck with my skid steer…
I took the wheels off and put on the wheel spacers. They were just over 2″ thick, which added 4″ of lateral stability to my SkidSteer… They went on pretty easily thanks to the old, but powerful socket driver my father left with me during his last visit. Basically, you bolt them on where the tire was and then use their new wheel studs to bolt your old tires back on.
After all 4 wheels were back on, it was time to get the tracks on… These suckers were heavy. I managed to lay out one side and drive the skid steer on to it, then I used a rope tied around the wheel to pull the track up onto the wheel as I drove forward. For the other end of the track, the only option was muscling it into place. I found it difficult to lift it and guide it properly over the tire treads, so I appreciated my wife helping out with that part.
Prowler provides some tools to help you wrangle the tracks together so you can slide in the carriage bolts. I am guessing that these tools probably work well with the other types of track that they sell (as shown in the instructions), but the Stealth rubber tracks have less space between them and it is tough to get the turnbuckle in place. Once it is in place, it tends to turn the rubber pads out of alignment rather than bring them together. Eventually, I managed to get the first track bolted on, but that was just the start. Once the track was in place, I was able to measure the slack and find that I needed to remove about 5 inches of total length. That is too little to remove a whole link, so you need to do it by unhooking and re-hooking individual links using the half inch shorter hole. This meant I was going to get lots of practice.
The instructions show using the turnbuckle tool positioned between the tires, and I did the first couple that way, but I soon found it was easiest to take advantage of the natural slack in-front of the tire. I could pretty easily move that link into position, the hard part was reaching inside to put the carriage bolt in place. As I got more and more links tightened, it got harder and harder to pull the track into position and I was back to using the turnbuckle for the last couple holes.
One problem with the turnbuckle is that it was pulling the tracks together in a way that rotated them so that I couldn’t get the bolts in the right place… I eventually solved this problem by adding stakes that kept everything flat. I eventually got the first track all tightened up. I had shifted 9 links.
I then shifted 9 links on the other track while it was laying on the ground. That was a lot easier. Getting the second track up on the skidsteer was also easier, thanks to some practice. But it still took me quite a while to get the last two bolts in place to secure the track…
How did it work out? Pretty well. I can now actually use the skid steer on my sandy site. I have since used it to save about $1000 worth of footings work. I also used it to unload a couple tons of rebar from the top of a truck. It moved a few hundred feet of 8″ pipe to the edge of a trench in one trip, etc… I am sure it will come in very handy for the rest of the construction phase… And then? Maybe I sell the skid steer with the tracks?
