Foundation repair for 1896 home


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Old 06-29-23, 01:35 PM
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Foundation repair for 1896 home

Condensed backstory: 1896 build with stone & mortar footer and stem wall, over the years crawl space was dug out, no retaining wall or foundation reinforcement added, erosion SEVERLY undermined interior of foundation, perched water table as high as roughly 77" below floor joists, still working on eliminating surface water intrusion.

So far I've built a new poured concrete footer 3ft inboard of existing all the way around, bottom of footer 75" below floor joists, poured a slab to replace poorly cast in place cellar stairs, laying cmu block 6 courses plus 4" solid cap inside the cellar and 8 courses plus 4" solid caps outside for stairwell. Footer is 16" wide x 10" tall with extensive rebar, slab is 6" also extensively rebar'ed. I laid 4" weeping tile behind the blocks, core bored four 5" holes and placed tee's for drainage into the cellar where two sump pumps will be installed.

New cmu retaining wall will have jackposts to bear some load of the house and stiffen floor.

Questions:

Should I remove weeping tile and drain rock to apply waterproofing to exterior of masonry? I don't mind water intrusion as the situation dictates that water drain to the interior and be pumped out but I don't want a structural problem.

In backfilling between new cmu and undermined existing, i planned to mix flowable fill something like 20 to 30 parts sand, 1 part portland, water to create a slurry and add large stones in the middle of voids just to occupy space. Thoughts?

Anyone have experience using expanded metal and sprayed on stucco (or something similar heavy on the portland) to encase the exterior of a stone foundation where the mortar is soft and crumbly? Better method?

I can give much more detail and possibly add pictures. If you've read this far I'd appreciate any insight you may have. Thank you
 
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Old 06-29-23, 02:46 PM
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Old 06-29-23, 02:50 PM
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Old 06-29-23, 02:54 PM
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Current progress, finishing 4th course and rebar bond beam
 
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Old 06-30-23, 10:17 AM
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Wow, quite the project! How are tying this new CMU foundation into the old one? Is this just intended to reinforce the lack of footings and leave the existing rubble foundation to support the house?

It's a bit outside my expertise, so I'll refrain from suggestions, but curious what others have to say.
 
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Old 06-30-23, 11:41 AM
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New work is a retaining wall to both stop further erosion and enable backfilling behind it to shore up interior of existing foundation. It will not be tied to the existing because the existing is too weak to justify the risk of drilling for dowels and likely a waste of epoxy trying to fasten them. New footer is literally nested into rock that I spent whole days chipping into like a friggin miner. Post and beam construction of the house makes lifting it unfeasible and multiple add ons make it even more sketchy, at least with my budget and time frame constraints. I'm hoping to fully encase existing with a sprayed on stucco type mix or possibly form and pour concrete both sides which I can then drill and bolt with stainless allthread and 4" x4" stainless plates.
 
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Old 06-30-23, 05:34 PM
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It appears in all 3 photos the floor joist are on top of a some type of rim joist to transfer the house weight to the old foundation. How are you going to have the new foundation remove the weight from the old foundation?
 
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Old 07-01-23, 07:40 AM
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House is a post and beam frame. The lowest wood members resting on foundation are those oak beams that serve as rim joists. Downstairs floor joists rest on inner half of the lengths of those beams while the rest of the structure is built off vertical posts resting along outer half of the lengths of those beams. Simply lifting at downstairs joists will rip them off the oak beams. I am building a load bearing wall around full perimeter of downstairs to place upstairs load onto downstairs floor which will be lag bolted to each downstairs vertical post. A complete second 2x4 framed wall up against the interior of existing downstairs wall. Also possibly adding glue lam beams sistered to existing joists where jackposts are located to better bear the cantilevered load at ends. This hopefully will enable enough load transfer that the jackposts placed along new cmu wall will take some, not all, load off existing foundation. That, in addition to fully encasing existing foundation, will hopefully allow me to leave existing in place as fully excavating it is simply not an option for many reasons.
 
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Old 07-14-23, 06:11 AM
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I decided to remove the weeping tile, filter fabric and drain rock I already installed to apply liquid rubber sealant. I have 4 courses laid, sealing to just past the bed joint of 4th course because I won't be able to reach behind after laying more. Still trying to decide on best method of repairing or encasing existing foundation. I'm leaning towards spraying a "portland paint" for bonding then parging with a 50% masonry sand 25% type S 25% portland mix on the inside. Outside I'm preferring digging to bottom of and slightly undermining existing, forming for 4" vertical encasement with rebar, and sloping the top of the concrete. I can then have a flashing piece made to go under the siding and over the concrete. I was really hoping for more feedback here, I'm not afraid of criticism.
 
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Old 07-14-23, 07:02 AM
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Outside I'm preferring digging to bottom of and slightly undermining existing
Very often the outside face of a fieldstone foundation of that era is not vertical as the inside face may be. One construction technique was to dig a trench with a vertical inside face and enough room to work in the trench and build the wall, backfilling the trench and then excavating inside the wall after it was built and backfilled. The lower sections may be thicker than the upper portion (like a buttress.) Undermining the fieldstone is usually not a good idea.
 
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Old 07-14-23, 02:32 PM
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Thank you, 2john02458.

My existing foundation is a footer and stem wall design where the stem wall is only a few foot at it's tallest point to compensate for ground slope and footer is roughly 1.5 to 2ft below grade. I'm pretty sure there was just a crawl space before somebody dug it out years later. In profile its shaped like an upside down mushroom.

Good call on undermining I'm sure. I just feel like the concrete should be at least as deep as the stonework. Frost depth in my area is 24"
 
 

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