Tag Archives: Concerns

Bedroom Shotcrete


Posted on August 18, 2016 by

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



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)_/¯


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.



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.


I guess I’ll tell the other stories here in the gallery.


Cleaning out the slag


Posted on May 21, 2015 by

Now this was a tough long weekend.FamilyCleanup

Basically, the basement of our earth sheltered home was filled with approximately 11 cubic yards of concrete slag that needed to be broken up and removed so we could prep for pouring the basement floor.

It was something we have known we needed to do since last year, but were putting it off for obvious reasons.



Here is the video:

Why did this mess happen?

All this concrete was wasted shotcrete that wasn’t on the walls and should not have been on the floor either.

As you may recall, I had used steel studs to frame the basement and then placed metal lath on the inside to “catch” the shotcrete.  I had been told (by the shotcrete guys) that the lath would be enough to prevent much of the shotcrete (peastone) from blowing thru.  I was told to expect a thin layer of concrete on the inside, thin enough that it would break up into small fragments just by walking on it and that it would actually save me from needing to add as much pea stone later.

Watching the shotcrete being applied, it did appear that not much passed thru when it was applied at a downward angle onto the previous shotcrete.  They did do it this way for the first couple levels, and actually raised a scaffold jack platform twice as they went.  But then they got a bit tired and started shooting horizontally and even at an upward angle.  This allowed much more shotcrete to pass thru.

The effect was cumulative with blow thru coming from so many different angles, each adding its own layer of concrete.  The round central room was especially bad for this with at least 3 layers of 2 inch thick concrete across the floor.

And once the crew was working on the inner walls, there was also “rebound”, shotcrete that doesn’t stick to the wall, and “trimmings”, concrete that is cut off the wall because too much was applied in the first place.

All this concrete (that I paid for) ended up on the floor, but not in a good, “wow, you got bonus concrete floor along with your shotcrete” kind of way.  On average, I would say we had about 3 or 4 inches across most of the floor (in several layers), and up to 8 or more inches near the walls, especially in the corners.  It was uneven and lumpy and even had boot prints in it.  The whole feeling was somewhat “war torn” and more than a little depressing.

When I setup the main level, I plan to back the metal lath with fiberglass screen.  The metal lath will still provide the strength to catch the shotcrete, but the fiberglass screen will prevent any material from passing through.





Thought I would try to put some extra pics in here…

And the Story.

I like to include the text of the video, along with some extra info that doesn’t fit in a narration, so that the content is google searchable.

For this job, I had hired some teens, rented a jack hammer and taken the day off work to make the long weekend even longer.

The big question was, “How would I get this slag out of the basement?”  The final solution that I came up with was a Bagster dumpster that I got from Home Depot for 30$.


The plan was to load it up and use my trusty skid steer in to lift it up and out of the basement.

It took a bit of trial and error to figure out the best way to lift the bag and to empty it, but fortunately, we had lots of tries to get it right.  You can see how we did it in the video.

The bagster is supposed to be for only a single use, but it  held up very well, load after heavy load, for a number of days. The only tear was caused by dragging it up the rough wall in the first lift.

TeensThis first day, we were mostly focused on the edges where the thickest concrete was because I didn’t want to rent that 75 lb jack hammer for a second day.  The heavy jackhammer was actually very effective on the thick concrete, but kept getting stuck in the thinner stuff.  For that, the 11 lb breaker was much more effective.  My Dewalt hammer drill also got a work out.  At the start of the day, I couldn’t get the teens to touch the power tools, but by the end of the day, they were much more comfortable with me and the tools and were taking turns on the jack hammer.

On Saturday, my parents were in town, even though I warned them that we would be taking on the worst job of the build so far.  I also hired Zack again, he was one of the teens from the day before.

My father got to cutting a slot in the footings (doorway) for the radon tube while the rest of us got cracking on the concrete slag.  Our radon tube was made of a 4 inch corrugated drain pipe, wrapped in landscapers fabric to keep dirt out.  It just gives radon an easy way to escape so it won’t build up under the basement floor.

Then my father and I worked on the floor drains while the others just kept right on cracking up that concrete.  In order to get the slope correct from the floor drain in the central room all the way to the outer wall, we had to cut open the tops of the footings.



We had planned for holes in the footings to run these pipes, and I had even come prepared with 4″ PVC to use to form them.  However, the guys doing our footings told me they brought their own 4″ corrugated drain pipe, which they nailed in place very quickly.  The problem was that the flexible pipe “floated” up in the middle when the footings were poured. Instead of being a straight sloped hole thru the concrete, they bowed to the point that we couldn’t even get the 2″ pipes thru.  I guess they were not used to the footings being so wide.  Narrower footings probably wouldn’t have as much deformation due to “floating”.  You may recall this same issue cost me time and money during several other stages of the build. Hopefully this was the last of it.


Then we came back out again on the holiday Monday, just my wife and kids.  Sherri and I cracked things up with the 11 lb “breaker” and the boys scrambled to collect the pieces into the buckets.  When the buckets filled up, one of us would dump the bucket in the bagster.  The boys were motivated by being paid 1$ per 5 gallon bucket.  They worked for several hours before wearing out.

With the big chunks finally removed, we raked the smaller bits and then brought in some pea stone, which is required by code in my area.

I came back on another afternoon with Zack and my friend Aaron to get the second half of the pea stone down and rake it all level.  At one point in the video, you can see Aaron intentionally took a pea stone shower, just to see what it would feel like.  I don’t think he will do that again.

BuildingPermit_blurThe final product was a a peastone under-floor that meets building code.  The black pipes are to channel radon out of the home and the white pipes are plumbing or drains.  The inspector approved the work and we were able to rake the pea stone level and move on to the next step.

Next step is to get the vapor barrier, insulation and radiant floor tubes down here so we can pour the basement floor.


Experience vs. Understanding


Posted on October 1, 2014 by

A lot of specialized experience and understanding are required to properly build an earth sheltered home.


Many contractors have experience, usually learned from mistakes made. Specifically, they learn from mistakes that negatively impact their portion of the build. They often don’t understand how the design or their adjustments and shortcuts will effect other portions of the build or the final performance. Many engineers have understanding of what effects the final performance, but don’t have the experience to understand how their instructions will be interpreted during real construction.

Contractors who do larger portions of the build are more likely to discover negative impacts of their earlier work and, therefore, build more experience.  A General Contractor (GC) sticks around for the whole project and hopefully accumulates more experience (via hindsight) that he can apply to the next job.  If you are GCing your own home, you need to figure out how to avoid mistakes rather than just learning from them.

Building Inspector

The building inspector is often a retired builder or someone with similar experience.  They should be on the side of the home owner and help to keep the builders in line with acceptable practices.

However, for practical reasons, their inspections are only at certain key points in the process.  The inspectors have a lot of other homes to inspect and can’t spend too much time at each one or keep up on understanding all the design intent.  Even with a good building inspector, there is still a lot of room for serious errors that the inspections won’t catch.  The GC and home owner still need to be vigilant.

For example…  The building inspector checks out the footings before the concrete has been poured.  He can see that the rebar and the forms look OK and may approve it, but he is unlikely to check all the rebar or all the forms.  Even if they do check the prep carefully, they may not see what is under it and they are not around when the concrete is actually placed and the builders are stomping the rebar into the ground.


Here are some anecdotal examples while I sort this out in my head…  I am sure I will see more as I continue my build.


The engineer understands that concrete is strong in compression(20 – 40 MPa or 3000 – 6000 psi), but weak in tension (2 to 5 MPa or 300 to 700 psi).  Reinforcement is used to increase the tensile strength and resist cracking.  The Engineer understands that when the concrete footing is under building loads, its top portion is in compression (unlikely to fail or crack), but the bottom is in tension and needs reinforcement.  at some point between these two, the compression and tension balance out to zero.  Therefore, the engineer will often specify that the rebar should be placed in the bottom of the footing.

However, the engineer also understands that the reinforcing is pretty useless if it is not fully encased in concrete so that its tensile strength can be shared.  So the engineer may specify something like placing the rebar 2 inches from the bottom of the footing.

Later, the guy installing the footing has none of this understanding.  If you are lucky, he knows that he can use rebar chairs that will put the rebar right in the middle and he will probably do that if you let him. When laying out the rebar, they may not overlap corners like they should or worry about rebar being placed in certain critical directions where the tensile load is likely to be greater.

In other situations, the installer may have no concerns at all about pulling the rebar or welded wire reinforcement (W.W.R) up into the concrete to place it at the correct depth.   They will just stomp it down and focus much more on the surface finish (that you see when you pay them) and not spend any time worrying about what you can’t see.

Getting this wrong is not something that they notice during the install (no failure as far as they can see), so you can’t trust them to get it right by experience.   The guys on my project made all of these mistakes and probably more.  I talked to them about these things as they came up and realized that while they have many years of experience installing footings, they had no real understanding of why they were putting in rebar or why it mattered where it went.  As a GC on your own home, you will need to keep a careful eye on your installers and inject some understanding (or just tell they what to do) as needed.


Here is a case where experience is the most important thing, probably because failure happens during the install.  An engineer can calculate lateral loads in mega pascals, he can understand how those loads translate into forces that will try to tear the form-work apart.  Meanwhile, the experienced builder has felt the weight of the forms in his hands and the compactness of the dirt under his feet.  He has seen these things fail and really wants to prevent that from ever happening again.

In my case, one of them said “put as many stakes in as you think you need to keep the forms in place, and then add two more.”

I still had some bow outs on my build because they overestimated how well the sand could hold in stakes, but generally speaking, their experience was an asset.

For my garage, the plans were a little unclear on the depth of a grove that was to be formed in the top of the concrete to catch the base of the wall.  I understood what it was for, but thought it was based on the depth of a 2×10 board (1.5″ x 9.5″).  The first guy to work on it had never done anything like this and did the work on a day when I wasn’t around, so he put the wrong sized board in the wrong place, etc.  I contacted the boss the next day and he send out someone else to fix it.  The new guy stiffened the board and placed it 3.5″ into the form.  While he was working, I noticed it was “too deep” and went to ask him about it.  He just looked at me and politely said, “I have done about 20 garage slabs for quonset huts and they always do it like this.”  Recognizing experience (and confidence), I backed down and went to check the plans.  He was right (and I let him know).