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Princelake
Member
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# Posted: 23 May 2018 10:14pm
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On my lot I have exposed bedrock and buried bedrock 1-2ft below the soil. My plain is to dig and drill holes into the bedrock and expoxy rebar into the rock. Next I plan to pour concrete sonotubes. Do I just put the sonotube directly on to the bed rock and pour? Or should I build and pour forms creating a pad to put the sonotube on to distribute the weight? If that's a good idea do I pour the pads then after pour sonotube on top or all as one? I plan to build 20x20 cabin what size of sonotube should I go with?
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DaveBell
Moderator
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# Posted: 24 May 2018 04:17am
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I would brace the tubes together into a matrix. And if too rickety, brace the matrix to trees or ground or if needed, epoxy 2x4x8 to bedrock then attach support brace next day. Pour whatever tubes can be done in one day (like outside tubes or at the corners), 25% depth at a time in rotation so the weight helps to add support. Use a level constantly. It also might be a good idea to do just a few tubes first and let them set up for a day or two to add rigidity to the foundation phase of work.
I would probably drill two holes diagonal offset in each tube brace point and bolt together with 1x4's and 1/4 bolts with large washers. Hammering or stapling probably not a good idea. Remember you have to step over the matrix bracing.
Take your time. The quality outcome of everything else above will depend on the foundation.
Can you post pictures of the site?
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sparky30_06
Member
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# Posted: 24 May 2018 07:25am
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How tall will the tubes be?
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snobdds
Member
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# Posted: 24 May 2018 10:41am
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You need to provide a base for the snotubes and tie it into the bed rock. I had the exact same thing going on, except mine was on a old glacial rock...
sono_tubes_4.jpg
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sono_tubes_3.jpg
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Ontario lakeside
Member
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# Posted: 24 May 2018 11:32am - Edited by: Ontario lakeside
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I poured my sonotubes directly onto the bedrock with rebar drilled it to the rock bent into a L shape. Aproved by my building inspector. I have a video if your interested.
https://www.youtube.com/watch?v=Mn4At5_8KJ0
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Princelake
Member
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# Posted: 24 May 2018 05:46pm
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I actually watched your video last night but couldn't really get a good look at your sonotube. I'm dealing with the same type of ground/rock as you being in northern ontario. So you dug some holes where the rock wasn't exposed drilled rebar then poured just sonotubes on top? No prep to the rock? Then exposed rock you cut the sonotube to form the rock and poured your concrete?
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Ontario lakeside
Member
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# Posted: 24 May 2018 07:21pm
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Yes exactly. No better foundation than a few million tons of granite! The cabin is dead level and stays that way.
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tasteoftaiga
Member
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# Posted: 24 May 2018 11:44pm
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My method:
- drill + epoxy, 3 bars per tube min
- cut sonotube as close to the profile of rock as possible with a priority on keeping it level (level check top in two directions and two sides of the tube)
- get a few buckets of loose sand, slightly wet is good, use this to pack the outside base of the tubes. This will give them a bit of stability when you pour
- recheck level
- use chicken wire to loop the wire around the rebar and then out through the tube near the top. Three separate times so you have three pieces of wire coming out of the tube to keep it stable. When tying off the wire do final level checks.
- repack sand that has loosened and pour
- checking level at 1/4 filled is a good tip so you can adjust if your form moved. A lot harder to do with a full tube.
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Princelake
Member
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# Posted: 25 May 2018 06:50am
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Thanks for the sand tip and chicken wire it's the kind of info I'm looking for. I could just see me cutting it to the rock the best as I can then struggle as concrete goes everywhere and everything goes off level. It would probably be smart do use like 10-12" sonotube so it can be more stable through the pouring process no?
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tasteoftaiga
Member
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# Posted: 25 May 2018 06:17pm
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I always use bigger tubes than needed, margin for error, because I make a lot of those.
I could have gotten away with 8" for my shed/shop but I went 12", glad I did because one post was slightly out of alignment and I just shimmied the beam a few inches off centre for that tube. If it was a smaller tube that wouldn't be possible.
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