I'm really confused about how to handle my cracked slab foundation. Over a 10(?) foot span, the room corner drops 1.5" compared to the height at the center of the room. Other cracks spider out in different directions.

I've been thinking about this problem for over a year. One book on the subject called Has your house got cracks? has offered some help. Written in England, most of its examples address Victorian brick homes. Their constructions methods are different, but the issues they face with clay soil are similar to what we have in Los Angeles county. My house was built in the 1960s, has no rain gutters, and had bushes and small trees near the problem area. My best guess is that poor water management, insufficient site preparation, and soil dessication (roots sucking up water) resulted in settling.

Strangely enough, foundation repair contractors near Los Angeles are a rare breed, and very expensive! You are thinking about all the earthquakes we have, and that LA should be crawling with these guys. I'm also shocked. So I'd really like some expert opinions from folks who see this and deal with it on a regular basis.

I've taken pictures and short videos to give a close up view of the problem. Let me give you the grand tour...

Main Cracks -
http://www.rosemarydrive.com/renovat...k_overview.jpg

The Context. Living room Overview -
http://www.rosemarydrive.com/renovat...n_overview.jpg

Crack running to mudsill - Is a footing crack implied?
http://www.rosemarydrive.com/renovat...ck_mudsill.jpg

Entry way settling - I wonder where the footing actually stops? Is it just under the front door?
http://www.rosemarydrive.com/renovat...y_settling.jpg

Crack extends across slab, through Dining room - The crack width seems much small in the dining room
http://www.rosemarydrive.com/renovat...ack_dining.jpg

The story continues in the backyard. Behind my backyard is 4 lane street, and beyond that is a railroad track. The backyard sits 5-6' above the street level, and the retaining wall is cracked and bowed. In the backyard I find fissures in the soil, one running for several feet.

Soil Fissure, up close -
http://www.rosemarydrive.com/renovat...crack_soil.jpg

What's the best way to solve this problem while spending the least amount of money?

Detailed videos -

Living room cracks
Backyard soil fissures/cracks

Option #1, The Pier Solution. Diagram showing cracks and heights -
One solution proposed was piering. The gentleman who gave me the estimate was kind enough to make a water-level mapping of the height differences in the foundation. His approach of using piers and void filling sounds very thorough. However, it doesn't address the flooring surface and it's very expensive - $18,000, or $20,000 if I use their engineer and get permits. Besides, I don't know if piers are truly needed here (maybe you guys can tell me). The authors in "Has your house got cracks" make the reasonable suggestion of accepting some settling if the cracks are no longer active. I don't know if mine are active.
http://www.rosemarydrive.com/renovat...er_diagram.png

Option #2, Uretek Foam Injection -
"We propose to inject Uretek foam to lift approximately 0.5" to 1". Sacrificial bottlejacks may be used if necessary, at a cost of $100 per jack." Cost = $8000 (no permits or engineering).

The salesman describes this material as hardening to a bowling-bowl consistency. I think this will work though I have some reservations. Raising the height of the room might destroy my new windows. I also installed new ceiling joists, and this was done while the room was out of square. Putting the room back into square might have strange results on the framing. And last but not least, this method does not address the cracks themselves or the flooring surface.

Option #3, Cut out the slab and replace, but leave the original footing -
I have two different quotes for this. The reps from both companies seemed on the level, but their pricing and the psi of the concrete are different. They propose:

- Demo and excavate
- Install 6mil vapor barrier and 1"-2" of sand
- Install epoxied 1/2" rebar mat at 16" on center, each way
- Pour 2,500-psi concrete, smooth finish
- haul debris
COST = $13,000

- Same as above
- Pour 4,500 or 5,000-psi concrete, smooth finish
COST = $4,850

I like this idea because I wouldn't have to worry about the windows or framing being disturbed, and the flooring surface would be perfect. $4850 is also much cheaper than $20,000. If I do have a crack in the footing through, I'm concerned that this method doesn't really address it.

Are these proposals any good? Is 1"-2" of sand really enough? How thick should the concrete be? What if they remove the floor and find fissures in the ground like I have in the backyard?

Option #4, Cut and repair cracks, pour self leveling agent -
I found this suggestion on You-tube, but I cannot find any company in Southern California that does this. I suppose I could attempt it myself, but cement is my worst area. I've read that "self leveling" thinset actually requires manual leveling and some skill.

Option #5, Use roofing shingles to level the surface, lay flooring
There's an article on AskTheBuilder.com that talks about using roofing shingles to level a small area of flooring. I plan to lay a floating floor, so this ingenious approach could actually work. However, my area is bigger and probably more varied than that author intended. This is the cheap and easy solution. Could it actually work? Would I be asking for trouble later by not doing something substantial now?

Thanks for posting. I realize it is a major source of stress for you, but this is one of the more interesting problems I've seen on this site.

Before picking a solution, I think you have to completely understand the problem. This could be a backfill problem, or there could be some deeper reason for what is going on.

I would suggest you ask a number of geotechnical engineers to give quotes on doing an investigation & coming up with recommendations. Money spent on investigation is not usually wasted... plus it will help at resale if you can point to this problem being thoroughly understood and then fixed properly.

Let me say I'm so impressed with your presentation. I need someone like you to look at my rehabs so I don't need to drive there.

How are the houses and ground on either side of you faring? Reason I ask is you mentioned a retaining wall which means some filled in ground. Also helps determine the depth of virgin soils there. I did get a kick out of needing an engineer. Where were they on the get when it was built, not to mention the building codes. That being said, to get a feel on how the structure was built and the common building practices in code would give a base line here is needed and not an engineer (yet).

My post will be long and for good reasons. I'm not an engineer but I have been using Crete and rebar for 33 years as a G.C. Let me say engineers are great but can really mess things up not thinking out of the box or just working off a set computer computation. Augured with them and won some.

Never wrote a book on Crete but lets define the word foundation on site terms.

The piers you have there are anything like I've seen on "Flip this house: then as far as I'm concerned they are nothing more then a pole barn or the “piers” being a fence post. A short history on soils that are soft. I build on PA. and also Puerto Rico for many years. Started as Mason first trade. Hurricanes hit P.R. many times over the years, and the buildings rarely crack much if at all. Also tons of rain there every fall. Soil does the trick along with a ton of Crete and rebar. We drive cars and pickups on the houses roofs.

What I see there. The piers are only as good as the footers footprint and the soil below it period. Its all about basics here, “compaction” strength and “shear” I could build your house on 4, 3” round concrete piers and not a separation or maybe not even a crack if the Crete was strong enough and enough rebar along with the piers handling the weight. Its not always about how many piers its about the footer under the piers and location/size of footer for compaction. Are there concrete lintels from pier to pier? If not then its sticks in ground and not tied in properly.

The ground there is obviously a moving sea. Note: Collage kids built a brick masonry boat and it floated. A woman from P.R. built a concrete room inside her newly built home. The code there states an all concrete home in Florida is not legal because of the soil being to soft etc. She finished her new wooden home and then later sneaked on a total concrete room ceiling and all. The last big hurricane came along and blew away the WHOLE neighborhood and she was found in here all block/Crete home safe and goos. NOW Florida is addressing its building codes for one reason “Her”

I see your house a boat that should be floating and its cracking and gapping and sinking. Just adding piers is not the issue at all. Its how far down does one have to go to get a good subase for a footer. Here's two structural ways to look at your house.

1.To have an actual footer that can support the weight intended for it and the Pier setting on that no matter what size the pier is handling the shear and compaction. That will be determined later for shear and compression once the footer/soil is figured out and clear span pier to pier and or lintels.

2. The other “foundation” is the floating boat proven theory. To more or less partially ignore the piers and build a Concrete floating floor. The piers would be to keep the whole house from tilting like the tower of pizza, but needed less for total physically support.

My approach before spending a ton of money is do some common sense research.
1. What are the neighbors yards and floors like?
2. How old are their houses?
3. Was the road bed cut down which would make your property higher in virgin ground or was the property backfilled in the back area leveled out ?
4. Knowing that the history so far, ask the city engineers what's the statute of in years for filled in ares to sit for it is be considered virgin ground.

As I understand it you don't need an engineer to do the flat work but for piers.
What is there now for a foundation and how deep is it?
The first bidder was on drugs to spec 2,500 Psi ( not sure why the make 2,500 except for slurry pour)
The second bidder was on the mark more. Another thing, do you have any fortified concrete there? What that is is 3 dimensional reinforced concrete. Here we put bags in on site truck and its basically rolled plastic screens that un roll and expand while mixing in the truck for all dimensional reinforcement/ The shingle method is outdated also. We have cementious Crete that's all but self leveling to negate shingles.

The 16 by 16 matt's aren't't enough to compensate the post settling there. The grid pattern of ½ bar should be 8x8 if its going to be mostly self supporting with center load concrete columns for cutting down the clear span. Many times I have use centered or multiply under the floor pads and conc columns to pour a monolithic pour and it rebared more coming of the columns to form a concrete lintel as we pour the floor. I don't have dimensions here at present.

I guess what I'm saying is repair in conventional means and spend less in thousands of dollars on to many engineers, the money diff can directly be put into the bar and Crete. There are basic building practices for self supporting slabs.

If you want an accurate possibly free scientific evaluation of the geotechnical engineers, start with a collage near by who has the current skinny on ground movement/ tectonics plates/ tremors/ soil composition/ etc and go from there.

Again bottom line, Find out the building codes and the neighbors slab/foundation problems. If your house and or their houses were built to spec then the specs are screwed there or its filled in ground that was missed on the specs. Or a water leak somewhere that can also easily cause this. Seen Mains here ruin several houses on a street. I keep alert on how you progress on this.

Hi 21boat - you make a very good point about the slab floating. If a slab of concrete is strong enough, then some settling or fissures shouldn't impact it. I had a conversation with the county site planner today, and I asked him if he thought 4500 psi concrete was appropriate, instead of using the standard 2500 psi. He responded like 4500 was crazy, "Why would you want to do that? It's not like you're trying to build a parking structure!". I actually think the strength of a parking structure would be great!! If it's worth doing, it's worth overdoing! =]

Apparently the county throws away site blueprints after 90 days, but they do have a soil map. I'm going to meet with the planner later this week to get an idea of what's under my house. I'll report back. I don't know if I'll be able to answer your questions about compaction and virgin soil though. Since the house is 45 years old, none of the original neighbors are still around.

I've asked a couple neighbors if they've seen any cracking or foundation problems. From their responses, I don't think most people want to acknowledge the problem if they have it. However, my plumber friend does a lot work in the track. On a recent slab leak job he found cracking far more severe than mine a couple blocks over.

Finally, it doesn't appear there was ever a leak under this part of the house. Neither the supply lines or sewer travels near the living room. With no rain gutters though, I wouldn't be surprised if water has swelled under the foundation.

Related Issue - Major garage crack

I didn't want to overwhelm the readers in my initial post. I probably did anyway! There's a related topic I'd like some help on though. A neighbor tells me that my garage was originally a carport, and the garage was built later. The cement is not as thick as the house. The walls bordering either side of the garage door are splaying outward, just slightly. The slab is cracking in the middle and it's much larger than anything in the living room. If I decide to go with the cret replacement strategy in the living room, it might make since to get the garage done at the same time.

Would a cut and replace approach make since for the garage? Are there any long term considerations with having slightly splayed walls?

Splayed Garage wall
http://www.rosemarydrive.com/renovat...rage_splay.png

Splayed Garage wall, larger context
http://www.rosemarydrive.com/renovat...y_distance.png


Garage-Driveway Threshold Crack
http://www.rosemarydrive.com/renovat...hold_crack.png

Garage Crack, room center
http://www.rosemarydrive.com/renovat...k_overview.png

Is the garage a block walled stucooed? If so it would be on its own footers The deflection there will get worse in time.

Little history in brick structures with full brick gable ends. The brick gable ends on very old homes and commercial buildings in my area have 1/2" or 3/4" steel rods to keep the floating gables from falling outward. My town was founded in the 1600s The "HEX" signs on the old Amish all brick homes is actually a integral structural element. The "hex" was a decorative way to hide that structural end and not just Blah plates showing on the structure.

The same thing needs done on the garage from end to end. Don't know how its going to effect the head room there. I've installed the rods systems on very old buildings 60 and 80 feet high to stop the movement. Oppsite Equal forces cancel each other out.

Nope, garage (and whole house) is light wood frame construction

That's even worse how can the wall lean unless the whole garage is leaning in the same direction?

I visited the County permit office today and got to examine a grading map and some soil sample results. It turns out most of the block is fill material. There were 3 soil samples taken on my lot in the 1960s. The results show "Type I" (clay, silty) exactly near the corner of the house where I'm having the problem.

Is the data below enough for an architect or engineer or some type to make a recommendation? (If so, please do!! )


http://www.rosemarydrive.com/renovat...estresults.png
http://www.rosemarydrive.com/renovat...ltypechart.png

* Expansive soils present at site. Recommend steel rebar in footings, 1/2 bar, one on top, one on bottom.
* Prior to placing fill, natural grade was sacrificed to 6" in depth, watered, compacted to a minimum of 90% of optimum density
* Natural Soils in place are of Type I
* Fill materials on site are 4' deep.


http://www.rosemarydrive.com/renovat...map-edited.png

One other good piece of news... the house is NOT in a liquefaction zone =]

I'm not an engineer and I don't know of one on the site yet. If there is it may be hard to get an answer because of the liability thing we created in the U.S.

That said.. I believe I see the engineering answer here for the depth you need to go.

Quote:

---

* Fill materials on site are 4' deep.

---

If the notation is right you need 4' plus to hit virgin soil. It's a bit of digging but its cheaper then engineers to find out digging 2' or 3' for ground solid enough to build on.

To confirm that I would dig down 4' and then get a core soil sample and get it compression tested for density and compaction.

The one thing I can't get over here is the 6" of top soil was taken off which is normal to save and dozer back over for top soil and the soil below it was watered, compacted to a minimum of 90% of optimum density, but who took the roller away too soon to compact the top 4' of the added fill?? A bit back wards where I come from..

My footers here need to be 3' min on the get go.

For your situation I have 2 designs to support the house and floors again I'm not an engineer. As long you can find solid ground..

The floating system I mentioned earlier makes it three ways to approach this if solid ground isn't found

As a G.C. I do jack up house and replace full basement foundations for a living in my area.

Hello,I just bought a home that's almost 2 yrs old and doors are not able to close nor fit in lock plate in door jambs,the moulding around the doors is spreading,my hardwood floors are spreading also and rising not even levels with each other,my foundation is cracking in the mortar coming from my basement windows forming stepcracks all the way down to almost the bottom cynder block and also the concrete floor is cracking everywhere,even the outside of the house on the foundation you can see step cracking and see the shape of the cynder blocks through which looks like there's water forming the shape of the cynder block then after a week or two you see it turned into a crack and a white powdery substance forms. Can anybody please tell me what's going on and is this normal behavior for a new home? I recently had the home warranty people over inspecting everything and the said if I can't fit a quarter in the cracks their not making the builder fix it.

Thank you so much for the tips about foundation repair! My wife and I found a house that we really like, and we're getting a killer deal on it because it is in need of some pretty serious repairs. But with your tips, and with a little bit of extra contractor knowledge from my brother, we figured we could make it work! Thanks!