Rock crackin’

Splitting bed rock open is usually a blast! A slightly more safe way is using feathers and wedges. Feathers… and wedges????

So you drill a hole, then you go find a suitable bird, pluck it…. Hey, in English it is called feathers and wedges! Could be confusing. But we are not talking about wedging a bird down the hole here.

This is what we are talking about:

The feathers are the two bent pieces of steel, cylindrical in shape and tapered towards the top. The bent part prevents the feather from falling into the hole.

I ordred 6 sets of feathers and wedge from a Norwegian manufacturer. I chose wedges made from Hardox steel as they stand up to the abuse a lot better than regular steel.

Product image from fjellkiler.no

I bought a big hammer drill that delivers 7 Joules to the drill bit. For scandinavian readers: I bought it from Jula for NOK 1799,-. The model is discontinued and replaced with a similar one. The one I got uses SDS-MAX bits and draws 1050W. The new model delivers 9 Joules and should perform better, I believe. In any rate, what you should aim for is a large machine that delivers a good punch. There’s no need to go completely overboard though, as you’ll ned drill bits that can stand up to the abuse.

I’ve found that the drill bits sold at Biltema does not last and should be avoided. The hard insert breaks off very quickly – a couple of bits did not last half a hole! I buy my drill bits from Jula. The V-shaped hard insert lasts a lot longer. I think the record for a Biltema bit was 5 or 6 holes, while I have a bit from Jula that has done 30 or 40 holes by now. It still works, but is pretty worn.

The specifications on my drill goes up to 20mm holes, so that is what I got for the feathers and wedges. My brother-in-law, who told me about this, has a lot of experience with feathers and wedges. He found that 20mm is a good middle ground. The machine drills the holes relatively fast, and the feathers and wedges delivers enough force to split rock without me needing to make Swiss cheese of it. You want to drill as few holes as possible as this does take time. The splitting takes seconds.

Drilling holes

The procedure is rather simple. Drill 20 cm deep holes (slightly longer as the wedges as there will be some dust left at the bottom) about 10-30 cm apart, depending on the rock type you’re working with, the amount you are trying to split off and the conditions within the rock itself (cracks and so on). Look for formations and cracks in the bed rock and try to make such features work to your advantage. A bit of experience will help you determine this as you work, so don’t think too much about it. A row of holes will usually result in a pretty straight cut line, which could be advantageous. Think stair steps in bed rock.

You’ll need to buy a handful of drill bits, as they will bust on you. The hard insert breaks off or wears out. It is a good practice to have two or three bits while working, swapping bit every 2 to 4 holes. They get very hot and needs to cool down. Do not plunge them in water; it will ruin them. If you are working in the rain, be aware of puddles of water.

FIRE IN THE HOLE!

…not exactly.

When the holes are drilled, it is time for the birds – but first we need some marinade! You need to apply some chain saw oil – or better yet: molybdenum disulphide (MoS2) grease. This increases the forces by a factor of 5 and prolongs the life of your feathers and wedges. You do not need a lot of grease, just a very thin film. The downside is that the grease gets full of dirt and rock dust, so you need to clean it off before using it again.

Insert the feathers into the hole and place the wedge between them. The feathers points in the direction in which the forces will act, so place them strategically. Here is an example on how to remove the top of a cupola-shaped piece of stone:

The central one splits the stone while the others lift it upwards. It came out in 3 pieces and leveled the area just as needed for the project.

I use a small 1100 g (2,5 lb) sledge hammer to knock the wedge in. In some cases where more persuasion is needed, I use a full-blown 4 kg (8.8 lbs) sledge hammer, but simply wellying like a monkey on speed is not advisable. You “do the round”, giving each wedge a whack. After you’ve done a round, wait and listen. Soon you’ll hear the distinct sound of bed rock rippin’ apart. The crackling and small bangs and pops are addictive, let me tell ya!

Listen to the sound after the seventh strike:

The stone in the video was big and heavy, and in stead of manhandling it out of that ditch, I split it into two manageable pieces I could safely lift. Easier than any other method. Big becomes small, heavy becomes light(er).

After splitting, use the hammer drill with a chisel with the hammer function activated (no rotation). You can chisel loose rock away. Sometimes you can remove big chunks exploiting existing cracks. The splitting also creates fractures that could be useful. I always start the job by probing promising areas before I do any splitting. No need to drill a hole to split off a piece of rock that just need a good welly with the sledge hammer, a quick *brrrrrrr* with the hammer drill or a nudge with a stone bar. You’ll soon gain experience and can determine where to try with great accuracy.

Tip: after splitting off a large amount of rock, probe the stone wall left behind with the hammer drill and a flat chisel. You’ll be amazed how much debris that comes loose.

After hundreds of holes, some of the feathers has taken a bit of abuse. I’ve used the big sledge hammer to… persuade… the wedges at times. It is not recommended, but ya know…. Welly it harder if it ain’t moving! I’ve ordered replacement feathers from the manufacturer. The wedges are still good, as they are made from Hardox steel. A bit mushroomed on the top, but I’ll grind that off.

Examples

Our house lies on top of a rock hill. The rock type is mostly granite, or to be specific: gabbro. It is very hard and brittle, rich in magnesium and iron. Good for splitting, bad for drill bits.

The top of the stone removed in the pictures above would’ve just pierced the surface where the third slate block with two holes next to the corner, are placed (image below). More images from this project can be found in a gallery at the end of the article.

Here’s another example. I placed the holes along a line in the bed rock. Two sets of feathers and wedges was all I needed. The rock split along the line, about 1 meter in length (3’3”) long before i could welly the wedges fully in. For the next row, I used 4 holes. I had to drill a relief hole to create a bit of lift from underneath. If the wedge locks up before you can drive it fully in, you’ve tried to take too much of a bite. A good technique is to drill a hole that will lift the stone upwards.

As depicted, it is possible to create a pretty smooth wall using this method. This future walkway will soon be finished. The distance from the house is about 2 meters (6.5′), so blasting would not be an option really. The walkway leads to a small patio in one corner of the property. To create the patio, we put up a concrete wall and split off a huge chunk of the small hill. The debris was used to fill the area behind the wall, before topping it off with gravel. In the “before” image, the line in the rock above the small green sprout shows how far back we went. It was a lot of work, but the result is well worth it! And it did not cost us more than a bit of electricity and a drill bit or two. And work, of course. It’s a good workout!

On the outside of my woodworking shop, we made a walkway. From before, you had to climb the stairs to the right and walk down a small ramp in order to get to the front of the house. Not anymore. At the same time, I laid down drain pipes. This resulted in a dry shop, as there were no drainage before. None! I had water seeping up through a crack in the wall in really wet weather (we live in Vestlandet, a rather wet region in Norway), but this solved the problem. And it made for easy access to the front of the house.

The project for 2021 is to make a walkway with a couple of steps down to the patio. The stone left over from the rock splitting will be used to fill up the last portion behind the wall. In the future, a small hut with a fire pan / fire place will be erected to the upper left corner. The small “ditch” in the bed rock pointing towards the pile of dirt, will be deepened in order to lay down drainage pipes. The house is built on blasted rock, which usually means very good drainage capabilities – but I still want to lay down drainage to be completely sure no water damages could ruin the day.

The total cost for all the areas where we’ve created more usable space? Around NOK 4500,-, which is about $550 – $600 depending on the exchange rate. And we can still use the tools in other places.

You will need to replace drill bits, and of course the wedges and feathers eventually wears out. Still, this method will cost you a lot less than the alternatives. Expanding concrete is a very good option, but it is expensive and it is soooo slow. You’ll drill the holes, fill them with the splitting agent and then wait. sometimes for days. With feathers and wedges, you get instant results – no water needed.

By careful placement of the holes, you can cleave a rock pretty accurate. Perhaps create stair steps in a rock formation. The angle and placement of holes can also be used to create a small ditch for pipes or what have you.

The only other option for removing rock is blasting, but you need special equipment, trained professionals (at least in Norway) and it usually involves a lot more damage to the area around. You need blasting mats, which usually involves an excavator – the snowball rolls fast on that one. And of course: it is dangerous and you could potentially damage the house. The ground floor of our house is built from Leca blocks (expanded clay concrete building blocks), and blasting near such walls might create cracks which will need to be repaired.

Of course, playing around with explosives is more fun, but in this day and age it is frowned upon if you do not have the paperwork in order…

A relatively small investment in tools has given us possibilities we would never have had otherwise. Add a pick axe, a sledge hammer and a stone bar, and there’s no stopping you!

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