When burying your home, structural strength is probably the most important thing, but a close second is waterproofing. My home will feature a number of layers of waterproofing (belt and suspenders analogy), but this layer of Blue Max liquid rubber is probably the most important. As usual, I did make some mistakes and we can get to that later, but first…
The Video:
Not Cheap:
I had used a different waterproofing on the basement that I have since concluded was totally inadequate. That stuff cost about 255$ per bucket. I decided to switch to Blue Max after seeing it done on another earth sheltered home I was involved with. The Blue Max costs 100$ less per bucket, but it goes on much thicker, so you get fewer square feet per bucket. Also, I had to buy a whole pallet to avoid shipping costs and get a bulk discount. I calculated that the whole pallet should take care of most of my surface area according to their coverage estimate… but with all the lumps and bumps and holes due to the rough shotcrete surface, we used it up at about double the rate and I will need a second pallet for the rest of the house.
Rained Out
An unexpected and very heavy rain storm washing away our work.
Getting rained out that first day only made matters worse. Expensive water proofing was being washed off the house and the day was shot…
But it turned out to be only a moderate disaster. Only some of the waterproofing really washed off, so the second layer went on nicely. Also, the lift rental company (Wolverine Rental) were really nice guys and let me keep the lift for free for a few more days to make up for the rained out weekend.
Finishers:
Basically, you have part of the crew shooting the shotcrete, and they need to keep moving to keep up with the concrete trucks. They can’t really stop to smooth it out.
When they are available, my Shotcrete guy charges an extra few hundred dollars per day per finishing guy. These guys come after the gunner crew and trim off the excess and generally try to smooth it off. Maybe “smooth” is a bit of an exaggeration, but “shaping” it does help to get rid of the worst lumps and bumps and splashes and slumps (if Dr. Suess did shotcrete). The expensive waterproofing goes twice as far on the smoother walls and the savings quickly pay for the finishing guys… Plus the smoother walls just look better and probably shed water better, etc.
So, paying for the finishing guys is a no-brainer. My only problem is that the finishing guys are not always available. I was only able to get them for 3 out of the last 8 shotcrete days I have had.
We had a finisher on site when we shot the right side, but none were available when we shot the left…
Bad timing:
As you may tell by the fact that I thought I could build this house in 18 months, I am an optimist. Optimists are generally much more pleasant than pessimists (or “realists” as they call themselves), but we do tend to get ourselves in trouble from time to time.
In this case, I thought that I would be able to get the next couple shotcrete sections in so I could bury the house before winter… Winter came early and that plan was derailed. Spring brought its own scheduling problems and now it is mid summer and we are still waiting on shotcrete.
This has left me with a problem of long term exposure to UV…
Ultra Violet Damage
UV rays destroy most things, especially insulation and rubber waterproofing. The Blue Max guys say I should get their product covered (buried) within a month. I couldn’t. I did try covering it with large sheets of 6 mil black plastic, and I am sure that helped, but I had to fight with winter storms to keep that on. It has been a long time and I am seeing some signs of damage, but fortunately not nearly as dramatic as what is happening to the rigid insulation.
A zoom in on the surface after months of UV damage. You can see the little cracks.
Paint Brush
Because of the lumps and bumps in the unsmoothed shotcrete, getting full coverage was very difficult. Sherri was doing touch-ups with a paint brush long after I was done with the sprayer. By the time she was done, we had only one single bucket of Blue Max left…
Sherri went back over most of the structure with a paint brush to get around all the little lumps and bumps… Using up even more Blue Max.
Gallery
As usual, here are a bunch of pics to round out the story.
An unexpected and very heavy rain storm washing away our work.
The rain washing away rivers of expensive (and probably polluting) Blue Max.
Here is the Quonset after the rain washed off our fresh waterproofing before it had a chance to set.
Here you can see the Quonset with a nice thick layer of Blue Max
Another pic of the Quonset
The space between these arches will eventually become our kitchen…
Here, I am troweling on some hydraulic cement to fill holes in the surface that would have used up too much Blue Max. It looks like a set from Star Wars.
Gravity pulls the shotcrete down and away from pipes and boards before it sets.
I chisteled away the shotcrete near the skylight curbs and then filled these voids with hydraulic concrete.
The wasps around here are huge… And the lift was very helpful.
Other times, we would just shoot from the top of the building. We all ruined our shoes.
It is much easier to spray from the lift if someone else is driving it. Here, David operated the lift so Hunter could spray.
The lift made the job much easier.
Bedrooms are waterproofed
The HDPE french drains were dug in and sloped properly before being covered in pea-stone.
Here you can see how much of the concrete rebound we had to chisel away while laying the drain.
French Drain, ready for Pea Stone. The sand is already very permeable, but building code in our area calls for Pea Stone anyway…
Here, the french drain is going below the plumbing and electrical
Here we are taking buckets of broken up shotcrete that was spilled inside while shooting the bedroom walls.
David approves
David had a bit of fun delivering pea stone in the skidsteer.
Dan testing his welds with some chin-ups.
At the end of the day, we had 2/3rds of the structure waterproofed…
Sherri went back over most of the structure with a paint brush to get around all the little lumps and bumps… Using up even more Blue Max.
At the end of the day, we all went up in the lift and got some photos.
The BlueMax changed the feel of the shotcrete and the boys enjoy hanging out up there…
We had a finisher on site when we shot the right side, but none were available when we shot the left…
A zoom in on the surface after months of UV damage. You can see the little cracks.
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.
