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stone work

Anchoring bolts in granite face

Perric Falcon

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posted 6 years ago

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Hello everyone,
I am attempting to build a shade shed for a few sheep, and I want to use the flat face of a large boulder of solid granite (the face of interest is about 20' tall by 35' wide). It is what someone told me is called 'highly fractured granite' so my question is: is it okay to just drill in a few inches in, set anchor bolts (rebar?) and pack in cement and when it cures be able to attach some roof beams that would extend out and meet wood posts 10' away, essentially creating a 16' wide x12' deep shade shed for the animals, that was attached to the granite face? I can make a pencil drawing to attach shortly but here is the boulder in particular. I would attach the bolts equally at 12' height, as this is the maximum height for zoning without needing a misc. structure building permit, perhaps three in total, every 4 feet?

The tree was burned from the fire and will be cut down.

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Devin Lavign

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posted 6 years ago

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You could something like you describe or....

You could opt for expanding anchor bolts like these

Since these are less common I will give a link to where I found these https://www.worldbuild365.com/product/slrwqova0/fasteners-hardware/anchor-double-expansion-bolt-with-hook-ring

There are also ones without the hook or eye and with threads instead to attach some other fitting

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David Baillie

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posted 6 years ago

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Hard to say without seeing the rock. If it was me I would do them in pairs to avoid bolt Shear on 32 inch centres starting 4 inches in from the edge I would use a 1/2 inch threaded rod minimum drill my hole 1/8th inch bigger all the way around and purchase some two part epoxy for fastening in rock not just expanding cement to minimize my chances of spawling. You used to have to have the special Hilti hit type 2 gun dispenser now you can buy it for regular caulking guns.I usually tack the header in place with tap cons just long enough to get my bolts in. As to whether its good enough, hard to say your call...
Cheers, David

Perric Falcon

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posted 6 years ago

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Thank you for the feedback, I will try a pilot hole in the coming days. The expanding bolt and some epoxy seems like the way to go and I have more familiarity with epoxies then cements.

Devin Lavign

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Oh btw just in case you haven't drilled rock or concrete, you will likely want to use a hammer drill. These are sort of like mini jackhammers.
.

You can often rent one at decent rental places, or buy one at most hardware stores. Some hardware stores do also offer rentals as well.

Perric Falcon

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posted 6 years ago

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Devin Lavign wrote:Oh btw just in case you haven't drilled rock or concrete, you will likely want to use a hammer drill. These are sort of like mini jackhammers.
.

You can often rent one at decent rental places, or buy one at most hardware stores. Some hardware stores do also offer rentals as well.

Thank you so much, I agree this is the way to go I just need to find a place nearby that rents one in a cordless or gas powered version. One location nearby had one for rent but when I described my intentions he did not want to rent it to me anymore.... I also need to find an Auger for 4" wide posts for the support braces to be set to attach the roof onto from the bolts if I manage that far. Thank you very much for your sugestions, extremely helpful!

Devin Lavign

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BTW awesome idea for shading your sheep. I am sure they will appreciate the work you do for them.

David Baillie

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posted 6 years ago

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Perric Falcon wrote:

Devin Lavign wrote:Oh btw just in case you haven't drilled rock or concrete, you will likely want to use a hammer drill. These are sort of like mini jackhammers.
.

You can often rent one at decent rental places, or buy one at most hardware stores. Some hardware stores do also offer rentals as well.

Thank you so much, I agree this is the way to go I just need to find a place nearby that rents one in a cordless or gas powered version. One location nearby had one for rent but when I described my intentions he did not want to rent it to me anymore.... I also need to find an Auger for 4" wide posts for the support braces to be set to attach the roof onto from the bolts if I manage that far. Thank you very much for your sugestions, extremely helpful!

If you are renting, rent a "rotary hammer" not a hammer drill. Hammer drills; great for cement and hole 1/4 inch or less granite and 5/8 holes; rotary hammer. Trust me your patience will thank me!
https://en.wikipedia.org/wiki/Rotary_hammer

wayne fajkus

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I doubt a hammer drill will work for this as concrete bits prob won't work for granite. At least not for me. I have tried.

Core bits for granite are generally sold to fit on grinders. They are diamond coated. They grind the material away. At 1/2" and smaller i have had them break in the hole. Get more than 1. Go slow. Use water. It doesn't take long. If its out of reach of electricity, a cordless grinder can do it.

I caution about anchor bolts cause the hole may not be straight, and it can wallow out bigger than the bit. There are epoxies on the market now that work well. They expand to grip the sides.

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Walt Chase

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Rotary hammer and epoxy. Put enough bolts in it to carry the load.

Devin Lavign

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Good call guys, I had not thought about the hardness of granite. I have used hammer drills in rock, but it was a lot softer than granite. Soon as I saw your other suggestions I smacked my forehead and thought of course.

Marco Banks

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Ditto on the rotary hammer. You'll save yourself so much time and effort. Any good rental yard with knowledgable staff can point you toward the right tool and the right bit.

Expanding bolts can split the stone if you crank them down too tightly, particularly if you've got the holes/bolts all lined-up in a straight line. Epoxy is a way of getting a solid bite into the stone so that the bolt will not pull out, but without cranking the expanding bolt so tight that it splits the stone. It also does double duty in keeping moisture from seeping into the hole, and then going through the freeze/thaw cycle which will eventually compromise the hold of the bolt.

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Travis Johnson

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I would dispense with the idea of using the rock as a side of the structure.

For the same money that you would spend on anchor bolts and rental of a drill, you could just buy a few more 2x4's, frame the shelter in a right triangle, and mount it on skids that you could move around. Even if you like this spot, you could park the sun-shed along side the rock face and get the same protection on the backside for the same money, and not be limited to just that spot for the sheep to bed down on. Time wise, you could build the whole structure by the time you drilled a single hole through granite.

I would frame the structure 48" on center, using plywood gussets on each side of the cut joint, then floor the unit over, or trench the dirt out so that the 2x4's were in the ground and the sheep could lay on a flat dirt surface.

I agree. Here's the link: http://stoves2.com