raising concrete slab in a tight spot

Help Support House Repair Talk:

RegularGuy

Member
Joined
Mar 9, 2016
Messages
10
Reaction score
0
Hi Guys!

I have an unusual concrete project. I have a single-thickness brick wall with a 30-foot by 15-foot concrete slap (four inches thick) enclosed by that brick wall. The brick wall is resting on the house’s foundation/footers and is tied into the roof and walls of the house but the slab is “free-floating” (not tied into the house) and is resting on unexcavated dirt which has sunk about five inches on one of the long sides. (The other long side has not sunk, and is fine). I want to raise the long side which has sunk to make the slab level.

Two mud-jacking contractors warned me that it would/might “blow out the wall” if it were mud-jacked and they advised me not to mud-jack the sunken side of the slab to raise it level. I would be glad for any repair ideas any of you guys have, but I was thinking about opening the brick wall in about five places on the one long side that needs lifting (removing about three bricks per hole) and putting one jack into each hole and slowly, uniformly, and carefully jacking up that side of the slab that needs lifting.

First question: Are 5 jacks the right number to lift the slab without breaking the slab, (and are five jacks more than the necessary number)?

Second question: When the slab is at the right level, how can I keep it there? One idea is to fill the void under the slab with wet concrete but I would need to distribute the wet concrete throughout the 30x15-foot area underneath the slab, to fill the inches under the slab after the slab has been raised level. Do you have any ideas about how to push concrete through a tube to get it where it needs to go?

Thank you in advance!
 

Snoonyb

Well-Known Member
Joined
Sep 30, 2006
Messages
4,303
Reaction score
871
Were it I, I would overpouer it, far less hassle.
 

RegularGuy

Member
Joined
Mar 9, 2016
Messages
10
Reaction score
0
Thank you very much for your response, Snoonyb. I was limited in the length of my post so I couldn't say everything I wanted to. But I have an inside room with a wooden floor (on sleepers) hanging in the air five inches above the slab. This inside floor is sagging terribly because it is no longer resting on the slab. How can I provide lift/support for this wooden floor suspended over the slab? There is a five inch (or so) space and I would need to stick something into this space to lift the sleepers which are as far as 15 feet away from where I can stand and then I would need to provide "permanent" support under those sleepers so they can be "permanently" connected back to the support of the slab like they used to be. Your thoughts, please.
 

Snoonyb

Well-Known Member
Joined
Sep 30, 2006
Messages
4,303
Reaction score
871
I see, and an overpower would be impractical.

Not knowing the space, use or loading, there is the possibility for tapered headers and the eventual employment of shims, for adjustment.
 

RegularGuy

Member
Joined
Mar 9, 2016
Messages
10
Reaction score
0
Thank you again, Snoonyb, for your thoughts. I would be grateful for your further thoughts on how to support and lift the wooden floor without raising the slab that should be supporting it. I could upload any pictures you might feel would help. Thank you again!
 

Snoonyb

Well-Known Member
Joined
Sep 30, 2006
Messages
4,303
Reaction score
871
I can only surmise, from here, but if the wood floor system is falling, proportionate to the supporting slab, the wood system is floating, and you can conceivably remove areas of the floor sheating, lift it sufficiently to insert a jacking device, or several, and raise it.
 

RegularGuy

Member
Joined
Mar 9, 2016
Messages
10
Reaction score
0
Ok. Thank you, Snoonyb. The floor is a beautiful, thong-and-groove, oak floor, nailed in an invisible way, as it was being installed. I did not want to ruin it.... The floor is tied into the walls and is sagging badly in the middle.
 

Snoonyb

Well-Known Member
Joined
Sep 30, 2006
Messages
4,303
Reaction score
871
Somethings going to have to give, and it'll probably be you.

Were you to successfully lift it, without it breaking, which is doubtful, you could then have a mud-jacker, infill the void.
 

tomtheelder2020

Well-Known Member
Joined
Mar 8, 2020
Messages
115
Reaction score
32
Location
95620
Are you sure the floor was originally fully supported by the slab? 5-inch settlement across a 15-foot span is huge. It seems unlikely a 4" residential slab could have that much settlement without major cracking - do you see evidence of that? If you are sure the soil settled do you know why part of the slab settled but not the rest? If it was poured on a wedge of loose soil, and the wedge was uniform for the entire 30-foot length, that MIGHT explain it, but once the floor was no longer bearing on the slab it is hard to believe the soil was loose enough to consolidate another 5-inches under just the slab load - unless something else was going on. The culprit in soil settlement is almost always water. I suggest you check to make sure there is no way water is getting under the floor.
 

RegularGuy

Member
Joined
Mar 9, 2016
Messages
10
Reaction score
0
Tom, thank you for your help! I learn as I go through life. I bought the house used and when it was originally constructed the slab was supposed to be poured on unexcavated ground. But they excavated the spot by mistake and then back-filled it. We know now that the fill was not properly compacted. Over the decades it has settled. No cracking is evident. The slab was originally a covered porch with one side against the house. The settlement is on the 30-foot side away from the house, where the rain and snow can get in when it is coming down diagonally. Later (but before we bought the house) half of the porch was enclosed as an inside room and the oak floor was installed on sleepers resting on the slab. I would be grateful for any ideas and help you can give me. Thank you in advance!
 

tomtheelder2020

Well-Known Member
Joined
Mar 8, 2020
Messages
115
Reaction score
32
Location
95620
Assuming the settlement has stopped, you now have a stable system. If your repair adds more weight onto the slab the soil might consolidate further. Preventing water from getting in should reduce - and possibly eliminate - further consolidation.

Supporting the outside of the brick wall might make mud-jacking viable. Something like a bench of crushed rock to the full height of the wall and a couple feet wide might add sufficient resisting force. Ask the contractors about that. If they try that route, the rock should be compacted into place in thin layers using a vibratory plate (granular materials compact by vibration, not compression).
 

RegularGuy

Member
Joined
Mar 9, 2016
Messages
10
Reaction score
0
Thank you, Tom and Snoonyb!

Tom, maybe that is the best thing. However, I have another idea on which I would like comments and brainstorming please. There is a few inch air space between the oak floor and the slab which should be supporting it.

I am now thinking that maybe the best thing to do might be to slide some kind of floor-levelers between the oak floor (on top) and the slab below and then expand the levelers to take up the gap and lift/support the oak floor. The expansion of the levelers would have to be something I could do from a distance of more than five feet in some places.

Your thoughts, guys?
 

RegularGuy

Member
Joined
Mar 9, 2016
Messages
10
Reaction score
0
I don’t really have a picture of exactly what I have in mind, and am looking for anyone's help please. I am looking to slip something into the few-inch gap below the sagging oak floor, along the top of the concrete slab that is supposed to be supporting the floor. Attached is one hypothetical design.
I cannot physically get close to the place needing support but must work from a number of feet away. In the product shown in the attachment, if it were (let’s say) two inches tall, I could slide this along the slab under the oak floor and then from a number of feet away turn that hexagonal bolt head to raise the height of the product so that it would touch/support the floor from below and bridge the gap between the slab and the floor.
 

Attachments

Latest posts

Top