I’m getting ready to start my own home on some property I’ve had for a while. It’s up on a hilltop with beautiful views and privacy. The only problem is the solid rock close to the surface. In most places the rock is 3 to 4 feet below the surface, but in some places it’s right at the top and inline with the footings. My question is what’s a good way to deal with this? Should I get a jack hammer and bust out just enough for the footing, and then backfill with gravel so it drains. Or is there better way? Any suggestions would be helpful. This is North Western New Mexico so lots of moisture isn’t a real big worry. Code says the footing depth is 18″. Also the rock is sandstone.
Thanks
Opie
Replies
the key word is solid couldnt you dig to the rock if it is in the way then drill holes to ankor rebar then pour up to or around , just a thought.
We pin to it and work with it, unless a full basement is wanted, then either jackhammer or blast, depending on how much. one of the excavators here has a BIG jackhammer mounted on the arm of an excavator.
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I have met the guy that owns this company. If he can't cut it nobody can!
http://www.rocktoolsinc.com/
The rock makes a better footing than removing it and building on a gravel base. You'll need to build some custom forms to go around it and drill and pin like Piffin said.
Also after you strip the forms goober up the concrete-to-rock joint with flashing cement like Karnak to keep water from seeping through the cold joint. Thats a code requirement around here
Hi Opie,
We are on sandstone hilltop too, and contracted out our slab. They just dug out a trench with a backhoe. Most of the rocks broke fairly easily when lifted. A few harder ones were pulled out intact. Then the resulting trench was filled. We wound up with a fairly massive footing.
kestrel
Don't know if you said sandstone or what. Some does break out easier than others.
the reason code calls for 18" is so the water freezing under it does not expand and heav it up and out of the ground. Attaching it to ledge will stop that, no matter how deep or shallow.
Found a couple pictures for your inspiration...
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Thanks for all the ideas. I don't know why I didn't think about pinning it to the rock. It's a very large and solid formation so I don't think it'll move. Thank you for all the ideas. It's good to have a place to go for answers
Opie
If you are going to build continuous footings with a short basement or crawlspace, then you may still need to use a jackhammer to get an adequate run for drainage. We just did a house where we leveled the excavation out as much as possible but we still needed to bring in a big machine with a hydraulic hammer to break up enough rock to run our footing drains. We had a big vein of rock that we needed to go down 3 feet. The first foot went fast and then nothing. This 30 ton excavator was shaking the neighborhood but only creating dust. It was the hardest rock he's ever seen (or so he told me). At $1,800 a day, I was sweating it for a few hours until we got to the required depth below the footing.
Is it rocks or ledge? If rocks, you might be able to shift them out.
jt8
A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty. -- Sir Winston Churchill
The ancient Egyptians scraped out the sand down to bedrock and then pounded that with a harder rock (dolomite I believe) by hand until it was smooth and level using water levels. So far the pyramids haven't collapsed or settled too much. There are theories but I haven't heard anyone come up with an answer as to how they got the things so square, something like a quarter inch in a hundred feet. I live in hilly PA and every time I throw a lawn dart it sparks off the rock under the grass. My 1930 built house has almost no settling cracks, digging fence posts sucks though and I'm not looking forward to digging in the footers for my deck.