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  1. #1
    Super Member _RaT_'s Avatar
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    Default My concrete block stemwall is falling apart

    I have a older cabin in the Lake Tahoe area. We get pretty intense snow loads, this winter we saw more than 630" of snowfall. The downside is that it really takes a toll on structures especially those that are questionable to begin with.

    The footing is super solid, the concrete block stem wall on a section about 25' log is terrible. I need to replace it. Its from 2 to 3 blocks high, 8X16" blocks. Its filled, I don't know it is has any rebar. My plan is to get under the cabin and pick it up with jacks, knock the block out and form it up. The usual rebar schedule both horizontal and vertical would be followed. Anyone ever done this or have other options I might consider? I have lifted homes before, but never completely removed the stem wall.


  2. #2
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    Default Re: My concrete block stemwall is falling apart

    What does the stem wall contact? Beam or steel? I would remove a section from the center and pour a pilaster with bidirectional rebar and work from there, use small aluminum forms and 12" tie straps if you have room for it to sit on the footer. I would say a 25' bearing stem wall in your conditions would justify a pilaster every six feet.

  3. #3
    Super Member _RaT_'s Avatar
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    Default Re: My concrete block stemwall is falling apart

    Quote Originally Posted by Fixemall View Post
    What does the stem wall contact? Beam or steel? I would remove a section from the center and pour a pilaster with bidirectional rebar and work from there, use small aluminum forms and 12" tie straps if you have room for it to sit on the footer. I would say a 25' bearing stem wall in your conditions would justify a pilaster every six feet.

    Your comments certainly make sense. The pilaster if nothing else would offer lateral reinforcement. Being that the footing has not budged a fraction of an inch makes me feel confident that what ever I put on it will hold. The stem wall has a 2X6 redwood mudsill anchored every 8' with 1/2" j bolt anchors. That is no longer code here in CA because of seismic code. Sitting on the mudsill is a 2X8 rim joist that ties 4X8 girders spaced every 4 feet OC.

    Thanks for your comments. Mark


  4. #4
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    Default Re: My concrete block stemwall is falling apart

    Look into LVL for additional reinforcement at critical points, it is stronger and more durable than regular lumber.

  5. #5
    Elite Member CurlyDave's Avatar
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    Default Re: My concrete block stemwall is falling apart

    Quote Originally Posted by _RaT_ View Post
    ...My plan is to get under the cabin and pick it up with jacks, knock the block out and form it up. The usual rebar schedule both horizontal and vertical would be followed. Anyone ever done this or have other options I might consider? I have lifted homes before, but never completely removed the stem wall.
    I did something similar about 30 years ago with my home. It was built with no foundation -- just redwood mudsills placed in, well, the mud.

    I jacked it up and poured a new slab and footers under it.

    You have the advantage of a slab to put your jacks on.

    Now for the bad news -- you need an engineer. The big problem I see is how do you join the new wall to the slab and the footer under its edge, if there is a footer.

    I would be inclined to just dowel vertical re-bar into the slab with epoxy, but first dig far enough down in a location along the edge of the slab to confirm a footer. Your engineer will have other concerns.

    You are either going to bootleg this or get a permit. A permit will add to resale value, a bootleg will always be questioned.
    40 Acres on a hill - fantastic view. JD 110 TLB, 4-n-1, 12" bucket, 18" bucket, Addington thumb, rock bucket (doubles as root grapple)

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  6. #6
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    Default Re: My concrete block stemwall is falling apart

    Rat I am wondering why pour a wall rather than redo with block? The nice thing with block is you can jack and replace a section at a time without having to lift the whole building.

    MarkV

  7. #7
    Veteran Member orezok's Avatar
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    Default Re: My concrete block stemwall is falling apart

    A couple of questions. First, when you say it is falling apart, do you mean that the block is fracturing and breaking away from the grout?

    As you are probably aware, the strength of CMU's per ASTM C 90 is 1900 net psi. (1500 is typically used in in engineering a composite structure such as a wall). The real weight bearing component of the wall is the grout.

    Second question. Has the structure settled any? If not, then you don't have to replace the block.

    I would chip away any loose spalled sections and just plaster it. The block is really just a form for the grout.

  8. #8
    Super Member _RaT_'s Avatar
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    Default Re: My concrete block stemwall is falling apart

    Here is a picture of the block stem wall. The footing is quite solid. The picture does a poor job of illustrating how the block is tilting outward. Basically the first row of block is sitting on a narrow strip of mortar laid up pretty high to accommodate a large gap to get the block on level.
    Attached Thumbnails Attached Thumbnails -cabin-footing-iii-jpg  


  9. #9
    Super Member _RaT_'s Avatar
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    Default Re: My concrete block stemwall is falling apart

    Quote Originally Posted by CurlyDave View Post
    I did something similar about 30 years ago with my home. It was built with no foundation -- just redwood mudsills placed in, well, the mud.

    I jacked it up and poured a new slab and footers under it.

    You have the advantage of a slab to put your jacks on.

    Now for the bad news -- you need an engineer. The big problem I see is how do you join the new wall to the slab and the footer under its edge, if there is a footer.

    I would be inclined to just dowel vertical re-bar into the slab with epoxy, but first dig far enough down in a location along the edge of the slab to confirm a footer. Your engineer will have other concerns.

    You are either going to bootleg this or get a permit. A permit will add to resale value, a bootleg will always be questioned.
    My neighbor is an engineer. the charge is a nice bottle of single malt scotch. I think the specs will end up being #4 rebar, 16" O.C. epoxied into the footing. At least two horizontal rows of #4 rebar as well. The sill will require upgraded attachment. 5/8" bolts with the large square washers. Biggest issue I see is pouring the concrete in a form that is tight to the mudsill. In other words, how do I get the concrete in the form and how do I ensure it is filled up to the sill. A friend in the construction business said they make a upside down pyramid hopper, hand feed the concrete and vibrate the form.


  10. #10
    Veteran Member orezok's Avatar
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    Default Re: My concrete block stemwall is falling apart

    Quote Originally Posted by _RaT_ View Post
    My neighbor is an engineer. the charge is a nice bottle of single malt scotch. I think the specs will end up being #4 rebar, 16" O.C. epoxied into the footing. At least two horizontal rows of #4 rebar as well. The sill will require upgraded attachment. 5/8" bolts with the large square washers. Biggest issue I see is pouring the concrete in a form that is tight to the mudsill. In other words, how do I get the concrete in the form and how do I ensure it is filled up to the sill. A friend in the construction business said they make a upside down pyramid hopper, hand feed the concrete and vibrate the form.
    The way California makes us build schools is to pour the footing to 1" below the bottom plate and then dry pack the space. This will insure full contact. The hard part on a completed structure like your is that someone will have to go under and back up the packing.

    The drypack has to be rammed pretty tight to be effective. Usually a 3/4" board and a hammer.

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