Replies

1. 
   Gabe | Jun 20, 2007 01:48am | #1

   I am hoping to build a storage shed on a remote piece of property this summer in preparation for future cabin building. The site I would like to use is on a granite slope. Does anyone have any elegant, simply ways to attach posts to solid rock for a foundation.

   Sorry but elegant and simple don't do well on granite.

   A lot depends on the angle of the slope and whether it's one solid granite hill or granite bolders.

   You could always get some equipment up there and drill holes into the center of post location, get those U plates with a concrete anchor pin in the bottom and insert into the hole, nail the posts to the bottom plates and your in business.

   Gabe

1. 
   4glo | Jun 20, 2007 02:09am | #2

   Thanks, gabe, for weighing in on this. The slope is appreciable--probably a 2' drop in 15' and the granite is a solid dome--the property is just south of Yosemite, which is famous for it's granite domes. We're doing the work ourselves and have limited familiarity with rock drilling...altho we do own a hammer drill which has made setting fasteners into concrete very do-able. Do you think this is adequate for the job at hand? Are there special bits for this beyond basic masonary bits? I'm assuming if we drill that some epoxy will also be necessary.

1. 
   Gabe | Jun 20, 2007 02:15am | #3

   You'll have to rent a diamond bit core drill for this job with slow rpm and water.

   Gabe

2. 
   Schelling | Jun 20, 2007 02:38am | #4

   Pour a short concrete column on top of the granite. If the granite is smooth, pin with a short piece of rerod. The column need only be tall enough to hold a bolt for the post base.

3. 
   silver | Jun 20, 2007 02:41am | #5

   If practical, I would think about pouring a small "footing" for the post-a 2'x 2' box fit to the rock...you should drill a dowel hole and grout it in but I didn't dowel my post footings on solid rock in my basement and they haven't moved.

   The perimeter footings are all fit to bedrock and doweled every 4' with
   1" bar but that took a huge compressor and rock drill.

   silver

   silver

4. 
   Piffin | Jun 20, 2007 05:20am | #6

   Drill the ledge and seat allthread in epoxy to use for mounting Simpson post hardware. Mix enough mortar mix to seat under the hardware

    

    

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1. 
   IMERC | Jun 22, 2007 02:46pm | #16

   bedding grout holds up way better tham motar mix...Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->

   WOW!!! What a Ride!Forget the primal scream, just ROAR!!!

1. 
   dovetail97128 | Jun 23, 2007 02:26am | #18

   Imerc, I second that ... non-shrink grout is what is usual for that application."Poor is not the person who has too little, but the person who craves more."...Seneca

1. 
   Piffin | Jun 23, 2007 03:17pm | #20

   properly mixed low water and packed instead of slopped in wet and a small shim of mortar woun't shrink either. The grout is definitely better though 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

2. 
   Piffin | Jun 24, 2007 03:44am | #22

   I wonder if maybe what you and Imerc had in mind was where the portland mortar or grout wouod be supporting the load, where in my concept it is there mostly to stabilie and give appearance to the threaded rod that is the support for the hardware or is the supporting hardwaare. I have some photos in my main PC I can get to some other time 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   dovetail97128 | Jun 24, 2007 04:32am | #23

   Piffin,

   You got it. That is what I was thinking of at least. My experience around the commercial and industrial stuff is that non-shrink is the material to use even if the column seems to be supported adequately by the column base. In residential is the column base includes the load bearing bolt or leg then mortar mix mixed stiff and packed well would be fine I suppose, I just reach for the non-shrink when this comes up for me."Poor is not the person who has too little, but the person who craves more."...Seneca

2. 
   Piffin | Jun 23, 2007 03:15pm | #19

   True - up to ten times as much PSI ratings, but most porches don't really need that. For mounting to support a steel beam holding the whole house up, yes. 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

5. 
   Steinmetz | Jun 20, 2007 07:48am | #7

   Lay out and mark centers for the posts.
   Drill out the first holes in each of the columns using a hammer drill and a 3/8" carbide drill bit. Flood often with water and retract the bit often to remove the 'slurry.'

   When all these have been drilled to depth, increase the size of bit to 1/2" then 5/8" and finally 3/4" use 3/4" O D machine bolt threaded anchors (shields) each of which have 3/8" machine threads. Cut sections of threaded rod to add to the shields plus nuts washers and post brackets.

   Good idea is to heavily coat the shields rods and nuts with grease to prevent corrosion andtry to flash around any area that will pool water close to the piers. Steinmetz

1. 
   4glo | Jun 20, 2007 09:46pm | #8

   Thanks for coming up with a possible hammer drill solution--it may very well work nicely as the granite in this area is easily friable--which also makes your suggestion of starting the drill bit small and gradually increasing in diameter sensible.

1. 
   Steinmetz | Jun 20, 2007 10:42pm | #9

   Aglo, did that many many times Saved big bux on carbide drill bits too. If you want to sharpen those carbide bits, it's easy and they will last much longer using a tried and true trick of mine. Buy a green grinding wheel (4" diam 3/4"wide x 1/2" hole) and an arbor to fit your electric drill. When bits get difficult to manage, sharpen the points along the original shape.(No need to be perfect here) Don't remove too much material. Also, the green wheel should run reasonably fast, while you traverse the whole face of the wheel (This will eliminate deep ruts,and presents a flat surface. The wheel cuts carbide because it is very friable so it won't 'glaze' since it's always presenting new sharp cutting abrasives.

   The green wheel is much cheaper than diamond wheels Steinmetz.

1. 
   4glo | Jun 21, 2007 02:20am | #10

   This is so cool! Not only do I get drilling tips, but I get solid gold bit-sharpening tips! Invaluable when the nearest hardware store is an hour+ on hairpin curves...Thanks!

6. 
   fingersandtoes | Jun 22, 2007 05:23am | #11

   Are you sure you want to use posts? You could pour concrete sono tubes. I built a cabin on oversized (2'-0") conc. posts. It looked very cool and didn't need any bracing the way posts do.

1. 
   4glo | Jun 22, 2007 07:04am | #12

   Hmmmm...sonotubes...I do like them as a concept. What system did you use to attach your foundation to the piers?

1. 
   fingersandtoes | Jun 22, 2007 07:56am | #13

   I used the sono tubes because the site was subject to flooding. They were on  soil. Where I have used them on rock I drilled two holes and mortared in 3/4" steel pins. Tie these in to your rebar and they aren't going anywhere.

   I often use 2'-0" sonos as footings for carports and extent them up 8 to 10 inches above grade. It protects the posts from being knocked over.

1. 
   4glo | Jun 22, 2007 11:31am | #14

   Again, thanks for the mention of the sonotube--appreciate your feedback.

7. 
   STAINLESS | Jun 22, 2007 01:55pm | #15

   Haven't had the pleasure before this. Greetings.

   I can second the epoxy for pinning to the stone. I have used wedge anchors in the past & notice that when checked for torque after only a few months they had relaxed somewhat. The threaded rod I had epoxy'd in, still made torque when checked over 12 months later.

   A small tube brush comes in handy when you blow out the dust after drilling, the epoxy works best when it adheres to the stone rather than the dust.

   If you have any issues with possible corrosion you might want to consider Stainless Steel rod or All Thread. You will have to size up from Cold Rolled Steel, as CRS has quite a bit more tensile strength than non-hardened stainless, however. 

   I like the idea of working on or with stone, what's a generation or two in the life of a stone thats already millions of years old?

   Reagrds,

   STAINLESS

    

1. 
   4glo | Jun 23, 2007 12:40am | #17

   Agree with you on the epoxy--had more than my fair share of expansion-type bolts that just didn't quite do the job...if you're going to put the effort in, might as well be bomber. Also agree whole-heartedly with you on the rock/stone mindset--while most women would prefer a rock on their finger, I was thrilled with 40 acres of solid granite under my feet...

8. 
   IdahoDon | Jun 23, 2007 10:49pm | #21

   For heavier loads we use short sections of sonotube to cast a 6" or so projection that then holds the post base.  A threaded rod expoxied in the rock and long enough to attach the post base to is used.

   Lately, after rediscovering the post bases with the threaded rod built in, this is about all I've been using for interior or exterior applications.  There are a few versions with the thicker being rated for nearly 4,000 lbs. if used floating without concrete up to the post base.

   For your application I think you'd be fine simply drilling the rock and epoxying in the threaded post bases, but it looks more finished with a short concrete column.

   View Image

   A neat trick when pouring columns of various heights to one level plane is to use threaded rod expoxied into the rock (or concrete footer) extended high enough to use long nuts connected to the post base. 

   The threaded rod allows easy adjustment and sonotubes can be placed over each threaded rod/post base; framing installed,  leveled, and braced; and finally the sonotubes poured with no chance of the elevations being off even a fraction.

   The time spent installing the extra threaded rod is minimal compared to all the jacking around getting wet concrete level and looking correctly.

   When we use these threaded post bases to pass through a slab into a separate footer, a number of wraps of tape ensure the threaded rod will move independantly of the slab if any movement occurs.

   These bases are also our go-to for applications that need support that will be buried in a concrete pour, such as to support a short section of concrete wall when adding a new footer.  With each base rated at 4,000 lbs for long term use, it's not unreasonable to use them with precase 10" square concrete bases every few feet to support a couple of stories long enough to get the new footers in.

   If your hammer drill is not the SDS type, but rather a normal drill with the "hammer" function you'll be amazed at the difference in speed of cut.  Pick up a 4" or 4-1/2" diamand cutoff blade for a mini grinder and it will take 30 seconds to repoint a masonry bit.

   If you want to add

    

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