# Basement Slab Settlement



## J&A Builders (Feb 3, 2009)

Got a question about a sinking slab. My parents house was built in 1986. The rear of the three story, walk out basement house, is sinking for one reason or another. A specialty contractor came by last year and "jacked" the footings in the problem areas. They couldn't raise the foundation any, but they did warranty against any further settlement.

My question is regarding the slab. From the front of the house to the back, it sinks about 2". Its not uniform, obviously, and mainly start sinking from the middle of the house to the back. It is pretty uneven across the back as well, causing gaps under the two exterior doors. I have racked my brain for a while trying to figure the best way to "fix" this. I can reset the doors no problem. The issue is leveling the floor.

The house is about 40' across the back and about 30' front to back, roughly.

Do I get floor leveler, which would require quite a bit by my calcs.

Do I re-pour the basement slab, in the sections that are the worst?

Do I frame a wood subfloor over the slab? which would effect every room in the basement, including doorways.

Anyone seen this situation and any suggestions?? thanks


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## Tinstaafl (Jan 6, 2008)

J&A Builders said:


> They couldn't raise the foundation any, but they did warranty against any further settlement.


Do they warrant the slab as well, or just the foundation? Before putting in much work on the _top_ of the slab, I'd want to ensure that it's not going to be dropping out from under whatever I do.


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## rbsremodeling (Nov 12, 2007)

Why do you want to level the floor?

What is on the basement floor now? Carpet? Tile?


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## CookeCarpentry (Feb 26, 2009)

rbsremodeling said:


> Why do you want to level the floor?
> 
> What is on the basement floor now? Carpet? Tile?


Sounds like it is a finished basement.


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## Heritage (Mar 20, 2007)

Was the walk-out installed AFTER the main construction? If so, was the section underpinned?

If it's sinking in one section, one remedy is to install heilical piers, this can be done from the outside.

As you checked the slope of the FLOOR, check whether there is a slope in the floor joists ABOVE. Check the outside for cracks and other issues that would point to the entire foundation sinking on one side.

If the slab ALONE is sinking, you have to work backwards on the construction of the slab and investigate. First layer we have the soil, then X number of inches of gravel fill (depending on your area/house). Then you will find possible insulation, dampproofing, steel mesh and the actual slab. An easy way to do this is to get core samples from 4 corners of the basement. From there, you set about fixing the issue.

Just adding levelling concrete will not correct the issue, unless you are confident that no further settling will occur.


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## J&A Builders (Feb 3, 2009)

There are some vertical cracks in the fnd. All this was addressed to the company responsible for installing the new reinforcing piers, the floor and exterior wall. The floor above appears to be level. I am guessing the slab is sinking independently from the wall, or so it seems. I need to put a level on the joists above to confirm, but I haven't noticed any dip, walking on the floor above. The warranty does not address the slab, as they only focused on the footings. Not sure if the slab is sinking with the footings or independently. If it sunk WITH the footings, then the company should warrant against any further sinking. Either way, needs fixed.


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## J&A Builders (Feb 3, 2009)

its is a finished basement, carpet. not a big deal tho, as it will all need to come up regardless.


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## cleveman (Dec 28, 2007)

How many flat holes do you see? Do you see excavators overgrading in some areas, then filling it back in and driving over it?

My guess is that the bottom of the basement was not dug out properly. We don't know if there is anything under the concrete, rockwise. Perhaps there is 12" of rock in some places where there were holes, then no rock in the high spots.

There are differing opinions on what to do regarding rock. In my area, there is 4" of rock put in, because the footings are formed up 4" and dug down 4". The rock may be 3/4 river rock, or some clean limestone, or some sand. I think I'm the only guy I've ever seen who compacted it.

Many don't believe that you can't compact sand, hence the term, "pounding sand". How many attached garages have you seen where the hole below (maybe 8' deep) was filled with sand, then the slab was poured? Then all you have is the perimeter lip holding the slab up and it soon collapses, leaving a cracked and sunken floor.

I could also see the hole being really wet and filled with rock and then the slab was poured. I imagine that as the clay dries out, it shrinks. Maybe it doesn't, but most things shrink when they dry out.

Let us know what you find.


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## J&A Builders (Feb 3, 2009)

4" of stone is required under a slab where I live also. I believe this is the case in most places. This house was built in 1986. I don't know what the code was back then, however, this problem started occurring about 4 or 5 years ago. I guess I need to drill some hole in different place to see if gravel is present. If not, then I guess that is my problem.

The thing is, the FOOTINGS were sinking. Obviously this caused a chain reaction, I am assuming, involving the slab. The footings are now supported adequately. 

Are you saying the slab could be sinking independently of the problem causing the footings to sink, due to a lack of 4" of gravel in certain spots?? The entire floor along the back of the house has depressed about 2" or so. I think it is related to the SAME issue as the footings.


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## Tinstaafl (Jan 6, 2008)

That was my first thought, that the slab itself doesn't have enough support under it. But if the only subsidence is right at the foundation, I agree it's likely to be just a symptom of the footer problem rather than anything more sinister, and probably won't give you any more trouble.


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## J&A Builders (Feb 3, 2009)

Moving forward, would the solution be; to bust up the problematic slab (I can remove the bad half up to the wall dividing the front of the basement from the back) and maintain proper a sub-grade and re-pour the slab? Or, would self leveling floor concrete do the trick. I think it would require a lot of self leveler. I don't knbow if that would be cheaper. Around here concrete is about 110/yd. To re-pour, it would take around 4.5 yds + need a pump truck to place it, all done INSIDE, through the doors and windows.

Does anyone know how much some good self leveling compound costs and recommend using it?

I apprentice all the advice.


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## J&A Builders (Feb 3, 2009)

sorry meant to say "appreciate"


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## Tinstaafl (Jan 6, 2008)

Anything you put on top of the existing slab is going to taper down to a thin edge, unless you practically pour a whole new slab. I wouldn't feel good about that thin edge holding well. I think I'd be inclined to remove and replace.

Either way, advice over the internet is worth what you pay for it. It would be best if you got someone experienced in to actually lay eyes on the situation. :thumbsup:


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## Anti-wingnut (Mar 12, 2009)

J&A Builders said:


> Moving forward, *would the solution be*; to bust up the problematic slab (I can remove the bad half up to the wall dividing the front of the basement from the back) and maintain proper a sub-grade and re-pour the slab? *Or*, would self leveling floor concrete do the trick. I think it would require a lot of self leveler. I don't knbow if that would be cheaper. Around here concrete is about 110/yd. To re-pour, it would take around 4.5 yds + need a pump truck to place it, all done INSIDE, through the doors and windows.
> 
> *Does anyone know how much some good self leveling compound costs and recommend using it?*
> 
> *I apprentice all the advice*.





> *sorry meant to say "appreciate" *


I think both terms may be applicable


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## J&A Builders (Feb 3, 2009)

The company that looked at it before was what I would have called experienced. They are one of only a handful of companies in this area that specialize in foundation rapiers of this sort. I would have thought they would have offered a solution or at least an explanation as to the cause of the slab issues. 

Anyways, thanks for the help everyone.

I am not really sure what anti-wingnut is saying. Feel a little insulted. I am just looking for some advise here. It is frustrating when the so called "professionals" don't even seem to to their job. I am a builder and know exactly how to prepare a foundation for a basement and slab. I don't know a lot about soil settlement and how to repair a sinking foundation without totally rebuilding. I have no idea what went on on this house in 1986. I was hoping the company we paid good money to would have offered us some solutions. 

Guess I'll have to get another "expert" to take a look...


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## Heritage (Mar 20, 2007)

J&A Builders said:


> Do I get floor leveler, which would require quite a bit by my calcs.
> 
> Do I re-pour the basement slab, in the sections that are the worst?
> 
> Do I frame a wood subfloor over the slab? which would effect every room in the basement, including doorways.


So you're a builder? In ascending scale, the aforementioned solutions are laughable at best. Frame a wood subfloor over the slab? WTF?:blink:

Especially one that's "sinking" 



J&A Builders said:


> Feel a little insulted. I am just looking for some advise here. It is frustrating when the so called "professionals" don't even seem to to their job. I am a builder and know exactly how to prepare a foundation for a basement and slab. I don't know a lot about soil settlement and how to repair a sinking foundation without totally rebuilding.
> 
> Guess I'll have to get another "expert" to take a look...


I'm highly skeptical of a so-called "builder" that doesn't immediately know what step to take in such a situation. The solution requires INVESTIGATION...not theories over the internet. CORE SAMPLES like I already mentioned is a good start and if you can't handle that by yourself... A detailed report from A STRUCTURAL ENGINEER, who will in turn contract core samples.

The friggin foundation of a house is just that!

If you're not qualified to do it...get professionals in there to ANALYZE, INVESTIGATE and come up with a solution in a documented REPORT of their findings and subsequent remedy.

It could be the size of the footings
It could be absence of rebar in the footings
It could be the MPA of the concrete in the footings
It could be absence of gravel beneath footings
It could improperly compacted soil beneath footings
It could be high water table in soil
It could be depth of footings
It could be improperly compacted soil beneath slab
It could be absence of gravel beneath slab
It could be the MPA of the concrete in the slab
It could be absence of rebar
It could be the type of soil the structure was built on
It could be absence of underpinning beneath walk-out section of basement


It could be a 100 different things you ding-dong! "Builder" my azz 

And then oooooh...you're "insulted" by Anti-Wingnut. :furious: OFF!


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## J&A Builders (Feb 3, 2009)

Dude, I know enough to take the right steps to fix the problem correctly. I am just getting advise from others on this forum. I am not going to do ANYTHING before I know exactly what is going on underneath the slab. I've got engineers looking at it as well as a couple building inspectors. I am sorry I even asked advise. None of them are resulting in friggin 3rd grade name calling tactics. Real professional bro. 

I have found myself in this particular situation, having a company already come out and install these helical piers, and the slab is still remaining needing fixed. Is name calling necessary? I mean what the hell? Thanks for the advise jackass...


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## Anti-wingnut (Mar 12, 2009)

Heritage said:


> So you're a builder? In ascending scale, the aforementioned solutions are laughable at best. Frame a wood subfloor over the slab? WTF?:blink:
> 
> Especially one that's "sinking"
> 
> ...


I stole this from JF:


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## Anti-wingnut (Mar 12, 2009)

J&A Builders said:


> Dude, I know enough to take the right steps to fix the problem correctly. I am just getting advise from others on this forum. I am not going to do ANYTHING before I know exactly what is going on underneath the slab. I've got engineers looking at it as well as a couple building inspectors. I am sorry I even asked advise. None of them are resulting in friggin 3rd grade name calling tactics. Real professional bro.
> 
> I have found myself in this particular situation, having a company already come out and install these helical piers, and the slab is still remaining needing fixed. Is name calling necessary? I mean what the hell? Thanks for the advise jackass...


The truth of the matter is that when a new poster shows up, claims to be a professional and then starts asking "how do I, how do I" over and over many older posters will view them with a jaundiced eye.

All your posts are apparently about this single subject, in the last few days. You claim to be a GC and a home builder. Most of us here would assume that a home builder would have enough experience to not need to ask a bunch of slack-jawed questions. 

Go ahead and get angry at those that question your professional credential, but you have brought these responses upon yourself. And the fact is, that if you weren't a new poster, you would probably not have recieved these responses. Posters who have been around a while, have answered questions and been part of the community get help better than those who show up purely because you need help.


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## TimNJ (Sep 7, 2005)

The footings have been stabilized and now you want to address the sloped slab, correct?
There are companies that will bore holes into the slab and pump a slurry mix under the slab. All the hydraulic pressure caused by this will inturn lift the slab up. The slurry mix will set up and that will keep the slab up. The only problem would be if you have running water such as a spring or something flowing under everything which will wash out the ground and cause everything to drop again.
I'm surprised the company that did the footings doesn't offer the slab pumping too. They should know a company that does the pumping/lifting work.


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## J&A Builders (Feb 3, 2009)

wingnut, I can defiantly understand where you are coming from. I don't mean to ask slack-jawed questions, its just that I have never dealt with a situation of this order. I know the right people to get involved to go forward with this. I just figured getting a little advise from some people who may have dealt with this issue before could help in my decision making. If I had known it would turn into a "lets bash this know-nothing idiot" fest, I would have never signed on. Regardless, I do value others opinions. 

I am trying to wrap my head around all that has been said and maybe I haven't been as clear as I could be.

In sum:
The foundation was determined to be sitting on weak ground.
The whole house has sunk, about 2-3" or so
Three Piers were installed to a depth of 70', along the rear footings guaranteeing no further settlement
The settlement is not noticeable on the first, second and third floors
It is noticeable in the basement, on the slab, from the middle to the back

I am thinking that the best alternative is to break up the floor, and repour a slab tying rebar into the reinforcing piers. I don't know if that alone would maintain enough support for the slab along the rear of the house. There are only three of these piers.

How do I determine if the slab won't sink anymore. Core samples will show me soil conditions and bearing capacities, but if they are deemed inadequate, whats next? Have any of you delt with a situation like this?

I'll admit that I have been a contractor for only about 5 years. I've got a degree in construction management, which taught me a lot about construction methods and materials. I am learning things every day. I don't claim to be an expert on any subject. Honestly, at this point I am afraid to ask any more questions. I thought that is what forums were all about.

TimNJ Thats good advise, kinda what I've been looking to hear.


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## JustaFramer (Jan 21, 2005)

Here is something to look into if you tear out the slab. Cut a keyway into the foundation walls to lock the slab in. Then epoxy re-bar dowels in the walls. Then do a double mat of rebar and pour a 6" slab. Of course you should talk it over with a engineer to get their approval. :thumbsup:


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## Mike Finley (Apr 28, 2004)

J&A Builders said:


> In sum:
> The foundation was determined to be sitting on weak ground.
> The whole house has sunk, about 2-3" or so
> Three Piers were installed to a depth of 70', along the rear footings guaranteeing no further settlement
> ...


The crux of the problem is do you do a solution based on the slab has stopped moving or do you have to demo the slab. Those are the two choices to me. 

If you demo the slab you're talking about excavation and or removal of the problem causing the movement. Is that removal and reinstallation of soil, tamping and drainage material? Install of french drains? Putting in peir system?

If the slab has stopped moving and the level and flatness is within some leveling products then that's the easy way out. Mapie makes some amazing levelers that can go easily from 2" to paper thin, probably some now that can go even more than 2", but you'll have to check with them.

How long of a time can you document that the slab has not moved?


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## Rio (Oct 13, 2009)

Sounds like a soils engineer might be called for.....................................................


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## Anti-wingnut (Mar 12, 2009)

J&A Builders said:


> wingnut, I can defiantly understand where you are coming from. I don't mean to ask slack-jawed questions, its just that I (can't help myself)


Good. We have reached the first important step. You have admitted you have a problem. First we tear you down, now we build you up. CT is a little like the Marines, but tougher.

So we'll assume that the house has been stopped from subsiding. It is safe to assume that settling of the floor can continue. You have three choices:

1) Live with it

2) Saw cut and demo the old slab, compact the fill, and re-pour. This can be very intrusive, but should give you a good result

3) Slab- (or mud) jack. Several holes are drilled and grout, lean mix or a CDF is pumped into the void beneath the slab and it is lifted. This is much cheaper and can be done more than once. It also may not work the first time


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## painter213 (Nov 2, 2008)

Slab Jack it with Foam. Inject foam inunder the concrete slab and raise it back into place. Works great!!


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## duburban (Apr 10, 2008)

How do they know how much foam when using the "slab jack" ? My casual experience with spray foam would suggest foam is difficult to control...


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## Anti-wingnut (Mar 12, 2009)

duburban said:


> How do they know how much foam when using the "slab jack" ? My casual experience with spray foam would suggest foam is difficult to control...


I don't have any experience with this product, but a modicum of common sense tells me that it may be just a little higher quality, with a slightly better metering system than "Great Stuff":whistling

I'll check Lowes tomorrow:no:


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## cleveman (Dec 28, 2007)

I've forgotten how many square feet are in the basement. Please tell.

Have you decided to rip it up yet and start over? 

Has anyone discussed what this mudjacking might do to any plumbing underneath? I could see PVC pipes being pushed every which way.


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## Anti-wingnut (Mar 12, 2009)

cleveman said:


> I've forgotten how many square feet are in the basement. Please tell


:clap: Funny one of the day :notworthy :thumbup:



cleveman said:


> Has anyone discussed what this mudjacking might do to any plumbing underneath? I could see PVC pipes being pushed every which way.


Fair question. The slab jacker I've been around know their stuff, and things like that don't get missed. But thru slab penetrations do need to be dealt with carefully


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## cleveman (Dec 28, 2007)

I found it in your first post. It is 1200 SF.

Now the question is how far down to go and fill with rock.

Since this was such a miserable failure the first time, I think I would contact a soil engineer and dig up some area first and have a look & see.

You may want to know what you're getting into before you rip out the entire floor and find out you need a grade beam every four foot on center.

If you have to commit harry carry or something, make sure you leave instructions with your # 2 to update us on the status of the project.

Maybe some guys can post some videos of underground rivers running through peoples basements.


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## painter213 (Nov 2, 2008)

It's controlled very easy. They can raise the slab up very slowly and accuratly. The use of foam is gaining ground in the slab jacking world now. As far as how much to use, I have no clue on that one. I just know that they bring enough to do the job and what is left over goes to the next job. I hope to take a class later on to learn more about it this year.


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## JustaFramer (Jan 21, 2005)




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## designbuildnj (Jan 24, 2011)

*Leveling Basement slab*

If I were you, I would serioulsy think about the budget. Obvioulsy to pour the floor in certain areas would come out the cheapest. I would seriuosly think about a liquid floor leveling system, especially if it's your parents home.


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## Teoli (Feb 27, 2010)

*Now I'm an expert*

OMG. What would we do without YouTube. In 9 minutes and 32 seconds, I learned how to level a slab. Now I'm an expert. In fact I had it figured out by 4 minutes and 52 seconds. It looks so easy.

Sorry, continue with the normal help and bashing. I've got more videos to watch. Next is....How to be a carpenter in under 15 minutes.


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## JustaFramer (Jan 21, 2005)

Teoli said:


> OMG. What would we do without YouTube. In 9 minutes and 32 seconds, I learned how to level a slab. Now I'm an expert. In fact I had it figured out by 4 minutes and 52 seconds. It looks so easy.
> 
> Sorry, continue with the normal help and bashing. I've got more videos to watch. Next is....How to be a carpenter in under 15 minutes.



Do you really think there is a 4 year apprenticeship for slab jacking. :laughing: If anything it's no more than a 16 hour class.


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