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Bolting Bible - Book of Rocks

“The harder it is, the better it is for your hole.”

EPISODE: Climbing bolts are only as good as the ROCKS you put them in

The Bolting Bible

The Book of Rock

Welcome to our free course as our way of contributing to the bolting community. It's nice to understand what you are clipping and trusting with your life, even if you never plan on installing or removing bolts. We believe that if someone is going to spend their time and money to bolt something, they probably want to do it as good as possible. Hopefully, the Bolting Bible gives you the tools you need to do a great job. Get it?

This book is in a blog format. The main blog points to all 17 chapters, and at the end of each chapter, it points you to the next. A downloadable pdf is available HERE.


Bolts Don't Hold You, Rocks Do

Bolts are only as good as the rock you put them in. Some rock is soft and some rock has more layers than onions. The rock, not the bolt is holding your life, the bolt is just hanging onto the rock. So let’s learn the basics to have a “rock solid” foundation!

General Rock Biology

It is important to understand the KIND of rock you are working with so you know what bolt will be the safest to use. To keep it simple, we will divide rocks into 3 categories. Hard rock, soft rock and layered rock. Rocks are made up of minerals. Minerals are what make, or break, the rocks’ strength. What you need to know about minerals are their hardness and their resistance to weathering. Quartz, a common sand grain in sandstone, and a common crystal in granite, is incredibly hard and resistant to weathering. Feldspar, like quartz, is incredibly hard, but weathers easily and turns into clay. Clay minerals are soft, and also weather easily into other soft clay minerals.

Hard Rock (not the cafe)

Hard Rock would be any rock that is, wait for it, incredibly hard, typically unweathered granite and quartzite sandstone.

Granite is the result of magma having cooled very slowly underground (plutonic rock) allowing the quartz and feldspar crystals (among other minerals not nearly as important) to grow big and tightly against each other, leaving no spaces. Yosemite granite is smooth from glaciers polishing them and Joshua Tree granite is rough because it sees very little water to erode it. But both formed and cooled underground and therefore are very strong. And both haven’t seen the excessive chemical weathering (think acid rain and/or seawater) to have turned the hard feldspar to soft clay.

Quartzite Sandstone is quartz-rich sand, cemented together with quartz cement. So the whole rock is nearly 100% quartz. Quartzites are the typical ridge-formers of sedimentary basins, like the Sandstones at New River Gorge, WV.

Bolts in hard rocks can be installed closer to an edge (within a foot or two). Strength of hard rocks is above 14,500 psi and goes up to 30k and even 50k psi for some.

  • MECHANICAL BOLTS - Granite or other hard rock is perfect for all kinds of mechanical bolts, just be sure they are stainless steel.

  • GLUE IN BOLTS - These work just fine in hard rock but there are 2 schools of thought. Glue ins can be frowned upon in granite as it can be considered overkill and replacing them can possibly be more difficult than mechanical bolts. The reason some people choose to use glue ins with fixed eyes is because there are no threads to get screwed up, no one can steal hangers, and the fixed eye allows highliners to thread static rope through rather than needing quick links. Glue ins typically have less visual impact than a standard climbing hanger.

Soft Rock

Soft Rock can be sedimentary or magma based. These are typically non-quartzite sandstones (where the sand-grains, or the cement, or both, are not quartz-rich, and thus prone to weathering and weakening), limestone (calcium carbonate), volcanic rocks, and excessively weathered granites. Just like tall tales, porous rocks with a lot of holes don’t usually hold up!

Sandstone is literally compressed sand, glued together with chemically precipitated cement. The cement and sand grains are made of various minerals, each with different hardness and resistance to weathering. When either the sand or the cement is not quartz, the sandstone tends to be much softer, because the grains/cement may have weathered to clay (or weathered out altogether, leaving pores). To “scientifically” test a rock’s hardness out in the field, hit it with a hammer! If the rock sparks, it's hard rock. If the rock breaks, it’s soft! You are looking for a solid sound and not a hollow thud.

Limestone is calcium carbonate (mineral name: calcite), often from dead marine life, squeezed together to make rock. Calcite is moderately strong, but it weathers into CO2 and water (i.e. nothing) when it reacts with acid rain. Think sinkholes and caves. So its structure tends has a lot of microscopic holes in it which makes it weaker.

Volcanic rock is from lava, so it cooled rapidly on the surface, not allowing the crystals to grow big and interlock. Also, lava tends to have lots of gasses dissolved in it, so as it cools it tends to be porous from the gas bubbles getting trapped. Small crystals and pores make volcanic rocks weaker than a slow cooling (unweathered) granite. Rhyolites and basalts, and volcanic ash “Tuffs” are typical volcanic rock names. We tested bolts in terrible volcanic rock in this EPISODE

Bolts installed in soft rock need to be placed further back from edges in the most solid part you can find. It’s also quite unsafe to put pressure on bolts installed in soft rock when they get wet, like after a rainstorm. Cyclic loading mechanical bolts in sandstone compromises placement integrity. In Moab, Utah, it’s highly recommended to let the rock dry out thoroughly before highlining on those bolts. In Zion National Park, you are not supposed to climb on that soft sandstone for 2 days or it will compromise the rock and gear placements. Soft rock strength (dry) can be as low as 500 PSI and up to 7,000 PSI.

○ MECHANICAL BOLTS - The softer the rock, the less force these will hold. Wedge bolts

are not recommended because the engagement contact point is quite small which can

compromise the placement in soft rock. Some sleeve bolts are ok because there is

more contact area (like 5 piece Power bolts - STAINLESS).

○ GLUE IN BOLTS - This is where glue shines. Glue gets into all the rock pores

therefore can pull on the entire rock surrounding the bolt stud rather than all the

pressure being placed on a few millimeters of the sides of the hole with mechanical


NOTE: Rocks fall (get it?) all over the hardness chart - and this is because of their varying mineralogy. It’s good to know the area you plan on drilling so you can install the safest bolt possible. Some sandstones can be very very hard like New River Gorge, WV (quartzite) and some granites can crumble in your hand like the kind at Cabo San Lucas baja tip (feldspar, aka “Arkose”, now weathered to clay-rich granite).

Layered Rock

Layered Rock is rock that has well-developed horizontal partings. In sedimentary rocks, these partings are bedding planes, where sedimentation stopped, and then restarted again. Sandstones, shales, and limestones can all be layered. In igneous rocks, especially granite, horizontal partings can occur that are called “exfoliation fractures”. These occur when igneous rocks are exposed at the surface and the pressure (of having been buried for millions of years) is released. The rock expands, and cracks like an onion.

Metamorphic rocks (slates in particular) tend to be layered as well, due to the shearing forces typical with metamorphic processes. Shearing causes the rock to foliate (or makes all the minerals in a rock align with one another in a preferred plane), causing onion like flaking, or part along the shearing plane.

Layered rocks can be tricky to bolt. The rock may be hard but comes with crack, and anybody on enough crack isn’t going to be reliable! An example of this is the Dinorwic Slate Quarry in Llanberis, Wales. (David Thexton) Another example of this is the limestone in Ontario as the limestone has been compromised by vegetation from the roots cracking it.

  • MECHANICAL BOLTS - can promote more cracking and are NOT recommended

  • GLUE IN BOLTS - Glue can grab the whole sandwich of rock layers giving better holding power.

Rock Inspection

SOLID ROCK - Regardless of what rock you are drilling into, make sure it is a solid piece! Hit it with a rock density detector… aka… a hammer. You can hear the difference of solid rock with a high pitched ping rather than a dull thud on hollow rock. You can also put your hand close to the spot and if you can feel the vibrations, the rock is NOT solid.

BIG ROCK - Be sure you are not just on some large flake or suitcase sized rock. Check to see if the rock is thoroughly attached to all the other rock around it and not just a boulder sitting in the dirt. Sometimes even car-sized rocks are just barely attached to a rock face. Your bolt might hold but the rock might not!

Think about the big picture of how that rock is attached to the earth.

Nothing is Forever

This is VERY interesting. This is Portland climbing area in the UK and posted by Dorset Bolt Fund who maintains this area. The bolts are installed correctly but the rock is eroding away! You can still see the glue surrounding the bolts. Climbing areas always need some sort of maintenance but this rock is like a melting ice cube. If you use an area often, find out if there is an organization that maintains those bolts and help them out with time or money.

What's Next?

You can always go back to the main part of the BOLTING BIBLE HERE

Feedback, typos or more information is always appreciated. HMU at

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