Date: July 20, 2024 - February 8, 2025
The first week of July as Ryan the excavator guy was fruitlessly scratching away at the bedrock, he told me about Betonamit, a demolition mortar product that will crack rock into chunks. So I googled it and read up on how to use it. The best price I could find online was a Home Depot special order for about $150 for a 44 pound box for an alternative brand called Dexpan. As you can tell by the date span above, to remove so much rock I would have been better off trying to find some locals who had experience with dynamite. However I lost my best connection to that old boy network when Clifton Peek, my neighbor and friend, passed away a couple years ago. So I ordered two boxes to give it a try and they came in shortly after Ryan and Brian had left with their Trackhoe and skid steer.
It would be nice if you could just sprinkle this stuff on and the rock would break. Instead you have to drill a 1.25" to 1.5" hole into the rock, mix the powder from the box with some water, then pour it into the hole in the rock, wait a day or two, and in theory the rock breaks up into manageable pieces.
A hole of over one inch diameter is way beyond even a super heavy duty electric hammer drill. This requires a rock drill driven by a sizable air compressor. I called the closest tool rental place but their rock drill was broken although they would rent a tow-behind air compressor for $160/day. (BTW When I was about 5 years old my Dad rented one of these compressors to drive a jackhammer to dig out under the house at 47 Edison.) I called all the other rental places in Asheville and one complemented the first place by not renting air compressors but did have a drill for $50/day. But the drill has three parts - the main drill which looks a whole lot like a 60lb jackhammer, the "steel" which is the shaft driven by the drill which has a hole through the middle of it to blow air to the cutting edge, and a bit which screws onto the end of the steel and does the actual rock removal. So the drill rental included a 12" steel but it didn't include the bit since those are expected to get worn out. The rental folks directed me to Asheville Bit & Steel Co down the road from them where you could get a 1.5" Tungsten-Carbide steel beaut for $120. One of those really old-time businesses with nice people where they still smoke inside the offices - wretched!
This bit was shiny when I bought it:
So the way these things are used, typically in mining activities, is you would use the 12" steel to drill an initial hole, then swap the bit onto a 3' steel to drill down further, and so forth, until you have a deep enough shaft. You'd use the same tool if you where blasting with dynamite.
I decided to use the old "pay one day's rent for a weekend rental" trick, and as luck would not have it, the drill rental place closed for the weekend Friday at 5pm, while the air compressor rental place was open Saturday morning for weekend rental pickups. So two trips into town. And it turns out the air compressor has a hour meter on it so when you take it for the weekend and pay one day's rent, you are only buying 8 hours of usage. I quickly decided that it is still a good idea to rent for the weekend so I could break that 8 hours into a Saturday and Sunday shifts because man this was hard work.
Weekend 1 July 20
Here are the photos from my first weekend session, starting with the "Airman" air compressor. Big diesel engine in there that burns a bit more than 1 gallon per hour - a considerably higher rate than the tractor:
Ladies and Gentlemen: the Ingersol Rand rock drill:
Hard to get to those upper reaches. Hard to hold it there when its bouncing around. But nice to have the front-end loader as a stable scaffold. Mighty dusty.
I've added arrows to the image below to show just a few of the holes after they were filled with the Dexpan mortar. I think I counted something in the neighborhood of 100 holes drilled in a weekend, which used up both boxes of mortar.
A nice haul - much more significant than were were getting with the rock hammer on the skid steer.
But although the drill went down 12", the rock grain is rooting the rock under layers to the right, so I wasn't getting a clean 1' slab off the top. That grain was also why the excavation machines couldn't make much progress. I started to get schooled on the composition of this metamorphic bedrock. However the process looked like it worked, so bought one box of the brand-name Betonamit for $224 from the rental place and special ordered four more boxes of Dexpan from Home Depot.
Weekend 2 July 27
I thought I could pick up the pace if I purchased a 3' steel and a 1.25" bit, so then I could drill deeper and take out less material on the lower part. Although the process of switching the steels made the drilling take longer, it had the advantage of giving me a little break (with the compressor turned off of course to stop that hour meter).
As the rock drill bores through rock it sends out a lot of silica dust, but it also spews grit and sand into the rock surface. This will quickly fill up completed holes nearby. So besides the litany of difficulties described above, I had to cork each hole as soon as I finished it with a rag. Sometimes those rags would get covered up with dust and I'd miss them when it came time to fill holes with mortar. So I'd try to work from top down to minimize that effect.
Here is situation at the start of the 2nd weekend with the complete drilling kit on display:
A bit of info about the drill operation which is pretty simple. The little silver lever above the right hand grip in the pic below is the air control: you push it forward to start the drill with variable speed - a little ways and it goes slowly, all the way forward (level) and it's jumping around like a demon. You can visualize that if the drill falls forward because the bit doesn't have a purchase in the rock then when it hits the ground the control switch gets pushed up to the off position. If you pull the lever toward you, then the drill does not engage but the air is blown through the steel and bit, cleaning up the hole and blowing dust and grit everywhere.
Anyhow, the two steels are used as follows: first drill 12" (you can see the rags in the previously drilled holes).
Then swap in the 3' steel and start from there and go way further down. That steel puts the drill handle at about head height, so to get it placed required bear hugging the seventy pound unit, lifting then staggering around seeking the hole without really being able to look down.
The mortar spec says drill every 12 to 15 inches. That's a lot of holes when you go to two dimensions. This picture is just after filling the holes on July 30:
Same perspective two days later on August 1:
Using the backhoe to encourage it to come apart:
Mostly the grain and texture of the rock would make it hard to get apart. However the grain worked in my favor on this corner:
The spoils after I'd pulled down everything loose:
Here again is the start-of-weekend picture to compare the progress. That longer steel was effective. On the down side, the steel bar in the center of picture above is six feet long.
Weekend 3 August 3
No pictures but it was the same routine all over. However the threads on the 3' steel and 1.25" bit striped so that was the end of that $250 investment. I decided to make do with 12" steel and just increase the area I'd get drilled over a weekend. When I returned the drill to the rental place on Monday morning I swung by Asheville Steel & Bit to ask if I could get a discount on a replacement and got a big negatatory bud. However I was describing what I was doing to the guy and he asked me if I was getting the mortar from Ideal Blasting Supply, a company about 2 miles down the road. I gave them a call and ordered 4 boxes of Da-Mite (knockoff brand, I guess) which cost $125 per box.
Weekend 4 August 26
I took a couple of weekends to train for my upcoming Ridge of the Rockies bike tour (details in other blog entry), then got in one more weekend of the rock assault before leaving for the ride. I replaced the long pin on the Kubota backhoe - it snapped in half from all the strain I'd been applying to it.
Back at it:
This one rock below (about 2' across) was separate from the main outcropping. It had been exposed by the big Trackhoe in July but didn't yield to it. It protruded just far enough to be in the way of the building. It is a completely different type of rock - it resembled solid granite. You can see that the mortar is much more effective at splitting a solid crystalline rock like this than it is with the layered stuff.
The mortar did its thing and some cracks showed but the cooler weather is reducing the effectiveness of the mortar:
After a determined attack with tractor backhoe and bar:
Another satisfying haul
October Hiatus
Hurricane Helene put a wrinkle into the plans, although we had minimal impact. Early in the month I put in another order for 10 boxes of Da-Mite since it was easy to see I had a long way to go. Also we made a trip to Blacksburg and brought a chunk of the old barn with us for George to use as a tree fort - actually it was the second delivery from the barn salvage pile:
Weekend 5 October 19
Although the hurricane cleanup was putting major demands on the rental equipment, I was able to reserve the compressor for the third weekend in October. No pictures, same routine. However the 12" steel provided by the rental place and the 1.5" bit threads were just about shot by the end of the eight hours.
Weekend 6 October 26
I had reached a layer of bedrock that was interspersed with decayed or rotten rock so switched to jackhammering. Depending on its composition, some minerals are affected by groundwater and break down. So after getting through the harder stone above I found these layers which didn't break when the mortar expanded - because it was too flexible. So on this weekend I rented a 68lb DeWalt Electric Jackhammer and broke the stuff up the old fashioned way. Also it was good for leveraging mortar cracks that hadn't come loose with the tractor or steel bar.
Even after two full days (no hour meter on the hammer!) chipping the main block I decided to extend the rental to work on Monday to tackle the corner of root cellar indent (that wet looking section behind the tractor below). Because water was running over that corner 24x7, the mortar I had used there just kind of stayed muddy and didn't hardly expand. With persistence the jackhammer would chip it out so I went back as far as I could before the rock got really hard. The pile of spoils was getting pretty impressive:
The corner was getting defined, and the surface I was working on was getting leveler, which was nice. I had got through the soft layers and was now ready to drill again. At left in photo below you can see the angular bite I got out with the hammer, as well as the trough I carved to try to keep the water against the bank instead of washing over the rock I wanted to remove.
Weekend 7 November 2
The air compressor rental place had by now repaired their rock drill so I rented it from them. That choice brought on a whole new level of misery. This rock drill weighed in at about 40 lbs and required that a lever be squeezed to turn it on, a bit like a bicycle brake lever, and it was hard to get it to run a variable speeds, which you need to get the hole started. As explained in Weekend 2 above, the better designed Ingersol Rand drill had a lever that you just moved to a variable speed position and it would stay there.
As any cyclist knows who has ridden down hill on a washboarded gravel road, squeezing a lever against a violently vibrating handle just destroys your wrists. Despite all that I persisted and got in my 8 hours but didn't take any pictures.
Although I had a couple boxes left, I put in an order for 8 more boxes of Da-Mite, this time getting the variety that works at colder temperatures.
Weekend 8 November 9
Once again rented the DeWalt Jackhammer. The days were getting shorter so I was wrapping it up Saturday night in the moonlight.
Weekend 9 November 16
Did another weekend of Jackhammer, but this time rented a 68lb Bosch from the place in Asheville. Cheaper than the DeWalt from the other place but I didn't like it as much. When I returned it I asked whether they had replaced the 12" steel for the rock drill, and they said they weren't planning on it and did I want to buy the drill for $150? That would be equivalent to 3 weekend rentals so I said yes, although of course I had to go down to Asheville Steel & Bit to get the new steel and 1.5" bit for $224.92. I sure as heck wasn't going to use that one from the other rental place!
Weekend 10 December 14
With my very own Ingersol Rand rock drill I put in another 8 dusty hours. Here is the Sunday evening shot of the grid of holes completed with rags corking them:
The colder weather meant that mortar took quite a bit longer to do its thing. Christmas intervened and it wasn't until the 27th that I got out there with the tractor and bar to pry the cracked rock out. The leading edge had big section cracked:
Which I was able to get loose with the backhoe. However, there was a lot more drill holes without big enough cracks to get the backhoe teeth into:
So I sought out small cracks I could use the rock chisels in. By "use" I mean start with a 3lb hammer then full swing whacks with the sledge. The audio on this slideshow is worth it only for the sounds of the bar when prying the rock - it brings it all right back to me!
One thing leads to another, and getting one rock out helps expose another that might be willing. At around 32 seconds into this one I demonstrate how to tell a rock will, with enough convincing, come out of its bed. Slightly hollow sound just like a good watermelon:
Then It Got Cold January 4
Nature's way of taking out rocks takes a bit more time. You got to have the volume up to hear the wall slowly crumbling.
Weekend 11 January 18
Back to the 68 pound jackhammer to get the easier stuff. I had exposed some layers of more crumbling substratum which could be pried loose pretty easily if the downhill side was already removed. So the process was to work from bottom to top loosening material, then use the tractor backhoe to scrape it out of the way, then start at the bottom for another pass.
The tractor serves as good calibration in this pic - it's parked at the finish grade, and the remaining rock only comes up to the base of the backhoe. Compare with tractor position on Weekend 1 above. The job is just about done!
Luckily jackhammering keeps you warm:
The wall keeps a two dimensional record of the weekends with the layers of drill shafts. Good shot of the layers of hard and crumbling rock:
Weekend 12 February 1
One more pass of drilling and mortar on the back slope. I had put in a call to Ryan the excavator guy to schedule Brian and the skid steer to dig out the footing ditches. I was thinking if I could use the mortar to get it loosened then we rent the rock hammer attachment again it might just work better than the frustration last July. And I still had 4 boxes of mortar which cannot be returned.
Above is the round of drill holes with rag corks. When drilling the holes on the slope on the far right something really strange happened. The last few inches of drilling met almost no resistance. Although I was wearing ear protection I swore that I heard the sound of water gurgling. I left the drill in the hole and took off my ear muffs but there was nothing. Next hole down the same thing happens. I think on the third hole I figured out that, because I cut off the drill when removing the ear muffs, there was no air going through the steel and bit. So I flipped the control handle into "blow out" mode and there was no question that the tip of the drill was sitting in quite a bit of water!
As I drilled I noticed one rock had some play in it, so I took a break from drilling to see if I could get it out and thereafter be able to drill deeper from its bed.
Set the phone down for some action strokes:
On Tuesday I got the holes filled with mortar and took a parting panorama:
Brian and the skid steer was expected on the following Monday, so the main task was moving that big pile of spoils out of the job site. This involved sorting out the stones by size so that they can be put to use down the road. The size categories were monster, rollable-but-not-liftable, liftable-but-still-hefty size, and everything smaller.
A couple of the monster category:
You only get the loader to pick something that big by hooking it under the top lip then pushing it up a slope. The hydraulics won't lift it but they will hold it once it's up.
That's it for the solo work on my Big Dig.
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