Thread: Foundation Slab Cracks

Need some help!

Inspected a house yesterday that was not finished and was being sold "As Is"
The bottom floor is a raised slab that has not had the carpet or flooring installed yet. The question was that there were several cracks in the foundation floor in addition to the normal expansion crack that would be found. These were migrating within the interior in almost every room. The question from my client is; Is this going to continue, Should this be happening this early and what is the remedy?

The pictures show the patterns of the cracks.


Jim Murphy

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Jim,

In my opinion, those cracks look significant enough to recommend a SE.

Are they going to continue? Probably so with my experiences.

What is the remedy? Probably foundation repairs.

To be safe, you could go with a structural engineer.

Concrete does two things:

1) it gets hard

2) it cracks

I always look for cracks in the places where I would expect them, i.e.,
- long narrow area will typically crack across the narrow width
- 'L' inside corners will typically crack from the inside of the corner into the slab at a 45 degree angle or thereabout
- large areas will crack depending on where the pressures build up
- that's why control joints should be cut into the concrete
- control joints *do not stop the concrete from cracking*
- control joints simply try to "control" where the cracking will occur
- sometimes mother nature will comply with the control joints
- other times she thumbs her nose at them and cracks where she wants to anyway

Originally Posted by JIM MURPHY

Need some help!

Inspected a house yesterday that was not finished and was being sold "As Is"
The bottom floor is a raised slab that has not had the carpet or flooring installed yet. The question was that there were several cracks in the foundation floor in addition to the normal expansion crack that would be found. These were migrating within the interior in almost every room. The question from my client is; Is this going to continue, Should this be happening this early and what is the remedy?

The pictures show the patterns of the cracks.


Jim Murphy

Not that I am questioning you but Raised slab? Could you give your definition of a raised slab.

Concrete block perimiter wall about one to two blocks high filled with soil, wire and poured with concrete. It is above the ground rather than at ground level.

I think if you pulled the carpet back on 90% of all slab (on-grade or stem wall) homes you'll find cracks that make you do a double-take.

Just an observation...

Originally Posted by JIM MURPHY

Concrete block perimiter wall about one to two blocks high filled with soil, wire and poured with concrete. It is above the ground rather than at ground level.

Well at a closer look at the pics the foundation/slab has serious issues. Being a raised slab with that amount of serious (not hair line) cracks the compaction below was extremely poor. the amount of settling that has taken place with all those cracks is far beyond what one would see with any slab.

The reason I asked about the raised slab is that they do pour slabs in place with the post tension cable an all installed and there are several piers in place that the slab is cranked up off the soil and is literally a raised slab. They do get cracks in the slab but would be hair line and the post tension cables pull it together from all sides.

Ted,

What Jim means, I think, is 'slab on compacted fill', versus a 'raised structural slab'.

Jim is just stating that it is not 'slab on grade' in the sense that it is 'raised up on fill' within the foundation stem walls.

Originally Posted by Dom D'Agostino

I think if you pulled the carpet back on 90% of all slab (on-grade or stem wall) homes you'll find cracks that make you do a double-take.

And, when there is tile instead of carpet, those cracks transmit up through the tile as 'cracked tile', and (in most cases) you can follow those same crack lines the slab by following the crack lines in the tile.

Thanks fellow,

Great job as usual. Love this site

Speaking of "raised slabs" does anybody remember back in the 50s when they began using hydraulically raising what they called "lift slabs?"

In certain soil conditions (think fill) concrete slabs installed on caissons is common and so are “raft-slabs” which are reinforced 8 inch thick slabs. We have many such types in the SF bay area and although they do well in seismic events they have a tendency to emulate the Titanic sans the iceberg.

The old 4 inch slabs, actually 3-1/2”, have major problems in that they used 6X6 wire mesh and/or ½” steel rebar reinforcement and punctured the hell out of the pitiful 4 ply plastic vapor barrier while pouring the slabs.

I don’t have to tell you that moisture quickly infiltrated through that membrane, attacked any metal reinforcement, cracking and heaving began, and the home owner law-suits grew exponentially. Most of the old timers who worked in the SF Peninsula are familiar with the saga of Foster City.

PS: How many are familiar with electric cathodic systems?

What's the remedy for something as shown in the photos?

Thanks,

Originally Posted by Raymond Wand

What's the remedy for something as shown in the photos?

If nothing is moving structurally, and it is likely that nothing is, then no remedy is needed.

I say "it is likely that nothing is" moving structurally on the presumption that both sides of the crack are fundamentally at the same height (one side of the slab did not drop noticeably in relation to the slab on other side of the crack).

Another thing which causes those slab cracks is that the footing is poured, the fill brought in and compacted (even when compacted properly), the walls of the house are constructed over the footing, the roof framing is installed bearing on those walls. Then the walls and roof finished, with all of those loads being transferred down to the footing and none 'to the slab' in the wide open areas (by design, that is the intent), the footings then compact the soil under the footing *just the tinyest, itsy-bitsy amount, the slab flexes over the unloaded fill in the center, and ... well ... as I said "concrete does two things: 1) it gets hard 2) it cracks" ... so the concrete cracks.

That may, or may not, be what is the cause of those cracks.

Originally Posted by Jerry Peck

And, when there is tile instead of carpet, those cracks transmit up through the tile as 'cracked tile', and (in most cases) you can follow those same crack lines the slab by following the crack lines in the tile.

Yes, but my point is that there are a large number of "undiscovered" cracks that preclude reporting explanations & SOP disclaimers/definitions, because they are concealed, yet still exist. Carpet, laminate, vinyl, engineered wood, tile- over-crack-suppression membranes, etc.

Many, many such cracks out there. Very few slabs go uncovered beyond initial construction. The issues are typically documented only after, or during, a remodel, or other floor covering replacement.

Dom.

Thanks Jerry, good info!

Originally Posted by Dom D'Agostino

Yes, but my point is that there are a large number of "undiscovered" cracks that preclude reporting explanations & SOP disclaimers/definitions, because they are concealed, yet still exist.

Dom,

I was agreeing, just expanding on what you said, then went into a related direction where those slab cracks 'could' be seen.

Originally Posted by Jerry Peck

Dom,

I was agreeing, just expanding on what you said, then went into a related direction where those slab cracks 'could' be seen.

And I was agreeing with your "agreement", just wanted to add some additional notes for those folks that don't see as many "post-inspection" conditions.

Sorry if I wasn't clear.

Originally Posted by Dom D'Agostino

And I was agreeing with your "agreement", just wanted to add some additional notes for those folks that don't see as many "post-inspection" conditions.

Sorry if I wasn't clear.

We live in crack heaven out here so to say we have serious amount of experience with concrete cracking is an understatement.

Those are not just hairline cracks. They are open and certain areas have settled and other followed or the edge of the cracks would not have the concrete chipped off of them. Yes concrete cracks but for a brand new home that is serious cracking that if things were prepared properly would not have happened.

My opinion it to have an engineer take his measurements and observations for evaluation to stop further movement and for possible fix for what is there now. At that stage already and more than likely future movement you could not consider tile work. More movement could have consequences to plumbing and out of square doors and cracks above and below windows and over doors and possible cracks in ceilings.

Again. The home is new and your client should be aware that if it moved that much all ready it will move more in the future. Cover you and your client with a recommendation of an engineer.

Originally Posted by Ted Menelly

--
.
Yes concrete cracks but for a brand new home --.

.
The Home maybe Brand New ( vacant for how long ? ) couple of years ?

Does not mean the slab is Brand New. Poured a couple of years before framing ?

Originally Posted by Billy Stephens

.
The Home maybe Brand New ( vacant for how long ? ) couple of years ?

Does not mean the slab is Brand New. Poured a couple of years before framing ?

Point is I inspect homes everyday that are in the five year old range. Only those that had concerns since day one had that much movement.

As stated above. Concrete cracks but to that extent in that short amount of time I would say the foundation/slab prep was pour and should be examined by an engineer. To not refer it to an engineer on a home that young and that much cracking would not be protecting yourself and client.

Originally Posted by Ted Menelly

Point is I inspect homes everyday that are in the five year old range. Only those that had concerns since day one had that much movement.

.
Just not Today.
.

Originally Posted by Billy Stephens

.
Just not Today.
.

Now Billy

I inspected a lot today.

The grocery store
Burlington coat factory
Post office
Joe's Crab Shack
My garage
My friends garage
My bathroom a couple times
The kitchen
Can' remember the ice cream place
Also inspected the different spots on my couch for different comfort levels
Bought an IR camera and scanned a few buildings for rats hiding behind walls (not)
Played with the new moisture meter
Now inspecting the frig for dinner and thinking of what kind of margarita I am going to have. Probably Patron Silver, Patron Citronge and Limeade

Man. I've been busy

Originally Posted by Jerry McCarthy

Speaking of "raised slabs" does anybody remember back in the 50s when they began using hydraulically raising what they called "lift slabs?"

Jerry Mc,

Several years ago I inspected a home that was constructed on fill in the San Rafael area, adjacent to the bay. The whole house was doing a "Titanic" and was several inches out of level. I felt like I was walking uphill/downhill whenever I walked from one end of the house to the other. The slab must have been a "raft" because there were no significant cracks in the slab and hardly any in the interior of the house in spite of the rotation that had occurred.

Originally Posted by Gunnar Alquist

The slab must have been a "raft"

I've seen those before too.

There are two ways to do a slab on compacted fill:
- where the slab is tied into the foundation walls (two ways to do that too)
- where the slab is a "floating" slab on the compacted fill.

When the fill settles, the first way just allows the slab to 'droop' in the center, with its edges still tied into the top of the foundation wall and being held in place there.

The second way allows the slab to settle which ever way the fill settles.

I've seen the first way with 2" air space between the bottom plates and the slab. The slab simply drooped and pulled away from the walls, leaving the walls "hanging from the ceiling joists". Those show up at interior walls and doors.

The second way, I've seen the floors dropped down about 3" all the way around the house, the first thing you notice is you step in the front door and the floor is not there, it is 3" down, leaving a curb effect on which the front door is placed. Then you begin to notice the other things.

The best sign of either of those is the use of over-sized base, wood or tile, used to hide the gap between the slab and the wall. The first time I found this condition I was trying to figure out why the slab drooped toward the center of the house, drooping in from all exterior walls. I accidentally (really) found some loose tile used for base and when I looked behind it I could see cut nails hanging down - they were originally used to hold the bottom plate to the slab, now they were in free air, with the walls hanging from the ceiling joists, nothing was visible around the ceiling/wall intersection.

Had me scratching my head until I found that loose base and could see what had really happened.

JP,

I did not see any separation or "hanging" wall framing. It was more like a boat that was rising on a swell. The whole house was tilted. I would guess that the slab had rotated so much that there was 6 inches height difference from one end of the slab to the other. But it was all in the same diagonal plane. No droop or sag. It was like being in one of those "mystery" house tourist traps that use sloped floors to make people seem taller/shorter.

Back to my original question. This foundation is only 3 months old from pour. I watched them build the house and just noticed the cracks because they had construction materials on top of them in the garage. My concern is the extreme length, one goes the entire length of the garage from front to back where it meets the thicker raised portion of the foundation of the house, while the other seems to go the entire back length of the garage at the seem. Almost like the right half of the garage is seperating. Would you buy this house? I have money invested and the builder is saying this is normal and if it doesnt get to be 1/4" wide or with verticle seperation no repair is necessary. I have not closed yet, scheduled for the 10th.

Originally Posted by Edward Siegle

Back to my original question. This foundation is only 3 months old from pour. I watched them build the house and just noticed the cracks because they had construction materials on top of them in the garage. My concern is the extreme length, one goes the entire length of the garage from front to back where it meets the thicker raised portion of the foundation of the house, while the other seems to go the entire back length of the garage at the seem. Almost like the right half of the garage is seperating. Would you buy this house? I have money invested and the builder is saying this is normal and if it doesnt get to be 1/4" wide or with verticle seperation no repair is necessary. I have not closed yet, scheduled for the 10th.

.
Not without a Home Inspection.
.

Originally Posted by Edward Siegle

Back to my original question. This foundation is only 3 months old from pour. I watched them build the house and just noticed the cracks because they had construction materials on top of them in the garage. My concern is the extreme length, one goes the entire length of the garage from front to back where it meets the thicker raised portion of the foundation of the house, while the other seems to go the entire back length of the garage at the seem. Almost like the right half of the garage is seperating. Would you buy this house? I have money invested and the builder is saying this is normal and if it doesnt get to be 1/4" wide or with verticle seperation no repair is necessary. I have not closed yet, scheduled for the 10th.

Edward, I think your original question was posted in a different thread.

Originally Posted by Edward Siegle

Back to my original question. This foundation is only 3 months old from pour.

the builder is saying this is normal and if it doesnt get to be 1/4" wide or with verticle seperation no repair is necessary. I have not closed yet, scheduled for the 10th.

Edward,

On the other thread, you stated it was post tension.

With post tension, if the cables were in fact tensioned, there should not be any separation.

Cracking, yes, concrete cracks.

Separation, no, especially not with post tension. The tension of the tendons should keep it all pulled together nice and tight.

You are asking us a question none of us can answer (should you be concerned/should you buy that house), not without 'looking at' the condition (the garage/house) and the cracking.

There are times when a home inspector will look at the cracking and say 'You need a structural engineer to address these cracks.', there are times when a home inspector will look at the cracking and say 'I see this type of cracking frequently, and it has (has not) been indicative of a problem.'

You REALLY need to have a qualified and competent home inspection in your area go out there and do an inspection, and not just for the slab, but the entire house.

If you only want 'the slab' looked at, then bring out a structural engineer.

If you are trying to save money and 'do it yourself', this is the wrong place to come for help. We can only comment on what we see and know, and if you want to 'do it yourself', then we will not know enough to comment on it, as it all likelihood the information you give us will be insufficient to address your concerns, as it has been to date.

You stated it was a $400,000 house, schedule a local home inspector to help you protect your interests, if you are not willing to help protect your interests to that extent, there is not much else we can say to help you out.

You came for advice, with insufficient information, thus the only advice we can offer is: Have a qualified and competent home inspector come out and do a full home inspection.

I'm sorry but this is getting out of hand. Your builder said to you that if the cracks did not get a quarter in wide there is nothing to worry about????????????????????????????????????????????? ??????????????

You need to stop right where you are. Call a home inspector. Have him go over that home with better than a fine tooth comb.

For any builder to say that to a buyer is ridiculous and is just smooth talking and covering up. I don't care if at this point they are only fine hair line cracks. Just his statement put him in the absolute no trust zone.

I had cracks similar to these in a house I had built a few years ago. I was concerned then and it turned out my fears were warranted. By the time I sold the house there were cracks going up the sheet rock in the same area. Just my experience but I would have them contact a SE.

Concrete Technology | Frequently Asked Questions (FAQs): Cracking | Portland Cement Association (PCA)

I see this in Pre-drywall inspections and call for SE. They typically say it's not a problem. Every case is different but that's the reaction I get most often. It is common around here also for the builder to say 1/4" or more we will repair, and anything under that they won't. I seen how they repair it also. Guy comes in with a mini chip hammer and "V" groves the crack. I don't know the cement mixture or fill they use though. I personally don't like it because the mix was wrong, dried out to quick, rained on, etc.

Just last week I inspected a 7,000 ft. home with basement. The finished basement had carpet and tile. The tile was cracked for about 10' and that's where the carpet started. I pulled the carpet off the tack strip and there was a crack in the slab 1'4" wide. So that crack started after the finish material was installed. That's another reason why cracks should be repaired.

In the early 90's I had poured a 24'X24' slab for my garage. Prepped the area myself and used fiber cement with wire grid in the concrete. To this day not one crack.

Because, other than Jimmy Hoffa and myself, few people have had the opportunity to inspect the underside of a slab, I am sharing these pictures.

Several years ago I inspected this house. Kitchen floor had a noticable slope, but no cracks in the tile floor. Baseboard was seperated from the floor by 1" at the exterior wall.

Builder should have stomped around a little longer and harder before the pour!

We talk about foundation movement but in reality it is the ground that moved.

rick

Originally Posted by Rick Hurst

We talk about foundation movement but in reality it is the ground that moved.

rick

Exactly Rick. This particular home has had way to much movement for a home of three months.

There is a thing called bounce back and that is what this may be. It is not from fill but from peeling of the top layers of soil leveling a lot. The virgin soil is now exposed and up to a year sometimes the soil will swell and then settle again If the house was built to soon over the freshly disturbed soil it may move around for some time to come.

Ted, I don't know if you were referencing the pic's I posted? The slab was raised on fill. As you can see it was truly a "floating slab". Here in NC piedmont we have a very expansive clay soil. If the soil was damp during the pour it would have been expanded, then after being covered it dried and shrank. I was very surprised to not see cracks in the tile.

I planning to buy a townhouse (built in 2002) and I noticed these 2 cracks. One is between this townhouse and the adjacent townhouse(the vertical one) and a piece of paper was covering it, coming from under the siding. The second one is in the other corner(L shape), the house is bumped out.

I did the inspection and the home inspector stated that there is no foundation issue. What do you think ?

Thank you for the replies,
Diana

Originally Posted by Diana Holiday

I planning to buy a townhouse (built in 2002) and I noticed these 2 cracks. One is between this townhouse and the adjacent townhouse(the vertical one) and a piece of paper was covering it, coming from under the siding. The second one is in the other corner(L shape), the house is bumped out.

I did the inspection and the home inspector stated that there is no foundation issue. What do you think ?

Thank you for the replies,
Diana

Hard to tell from the pictures since they're so close up.... My first reaction is that I agree with the HI. Also, it's hard to really get an idea of the whole setup with the siding and ground covering so much .

The second picture appears to be a cold pour joint. Two batches of concrete poured at different times.

Pull back and take another picture. All I see is what Raymond has said and ruff aggregate which they just didn't parge/skim coat.

Thank all for your quick responses. I feel more confident now.
I wish I could take another picture and actually look more closely at everything but I did this during the home inspection. I'll probably get to see everything one more time only at my final walk through. The inspector didn't suggested anything else but I couldn't stop thinking about it. Most of the floor was covered with carpet, hardwood, and tile(newly remodeled bathroom) so there was not much to see. On the outside I didn't see anything else.
Thank you again,
Diana

Originally Posted by Edward Siegle

Back to my original question. This foundation is only 3 months old from pour. I watched them build the house and just noticed the cracks because they had construction materials on top of them in the garage. My concern is the extreme length, one goes the entire length of the garage from front to back where it meets the thicker raised portion of the foundation of the house, while the other seems to go the entire back length of the garage at the seem. Almost like the right half of the garage is seperating. Would you buy this house? I have money invested and the builder is saying this is normal and if it doesnt get to be 1/4" wide or with verticle seperation no repair is necessary. I have not closed yet, scheduled for the 10th.

Go with your gut Edward, it usually is right. If the builder won't fix it now, you'll have to when you go to sell if that buyer has an inspector worth his/her salt. it's not going to get any better but could develop into something much worse and costly. Why take on that burden hanging over your head @3K per month for the next 30?

Take a hammer or solid bar and tap around on the floor. This will allow you to hear any hollow areas under the slab. If you hear a difference in the echo that would mean there is a void. If there's a void the soil or fill has settled. If the there is settlement below you may want to consider getting the floor slabjacked ...to fill the voids and even raise the floor if req'd. ( if you buy the place ). There's a cementious mudjacking material and there's HDP.
The mud simply flows in a lays on the highest layer.
See if you can get HDP ( high density polyurethane ) injected. You will get a material below the slab which will fill the voids completely because it goes in through the floor as a 2 part liquid, penetrates any voids all the way to the ground level...then chemically it begins to foam up filling voids, nooks and crannies...will lift and seal the floor and cracks...and will insulate the floor.
The SE is good advice! jim

Take a hammer or solid bar and tap around on the floor. This will allow you to hear any hollow areas under the slab. If you hear a difference in the echo that would mean there is a void. If there's a void the soil or fill has settled. If the there is settlement below you may want to consider getting the floor slabjacked ...to fill the voids and even raise the floor if req'd. ( if you buy the place ). There's a cementious mudjacking material and there's HDP.
The mud simply flows in and lays on the highest layer.
See if you can get HDP ( high density polyurethane ) injected. You will get a material below the slab which will fill the voids completely because it goes in through the floor as a 2 part liquid, penetrates any voids all the way to the ground level...then chemically it begins to foam up filling voids, nooks and crannies...will lift and seal the floor and cracks...and will insulate the floor.
The SE is good advice! jim

Study up on HDP you guys. This material penetrates and flows through the gravel, down to the virgin soil base...then chemically reacts and becomes a dense foam..
It will solve this type of problem down to virgin earth level and requires no tie in to the perimeter.

Originally Posted by Diana Holiday

I planning to buy a townhouse (built in 2002) and I noticed these 2 cracks. One is between this townhouse and the adjacent townhouse(the vertical one) and a piece of paper was covering it, coming from under the siding. The second one is in the other corner(L shape), the house is bumped out.

I did the inspection and the home inspector stated that there is no foundation issue. What do you think ?

Thank you for the replies,
Diana

I think some posts got sidetracked back to the old posts and forgot about this new one above.

The second photo shows either a cold joint from two different pours or, more likely, lack of proper consolidation during the pour (anyone recall when they saw ANY consolidation on a residential job? ).

The first photo COULD BE from the same thing but not enough is visible to tell as it also looks like it could be a crack which has separated laterally (horizontally). If the slab as separate THAT FAR it would be visible in the inside of the home, so I am inclined to suspect that it is just poor placement of the concrete - have your inspector jab a long screw driver or some other like object into the crack and see if it hits concrete in just a short distance or if it is indeed a crack through-and-through.

If it is a crack, or the person checking it suspects it is a crack, then it is time to bring in the structural engineer and let them design appropriate repairs.

Just not enough information to be able to guess any better than that.

Originally Posted by Jerry Peck

...more likely, lack of proper consolidation during the pour (anyone recall when they saw ANY consolidation on a residential job? ).

When I read this I started thinking back to last time saw consolidation on the job, then I remembered, I have no idea what you are talking about.

Care to elaborate?

Originally Posted by chris mcintyre

When I read this I started thinking back to last time saw consolidation on the job, then I remembered, I have no idea what you are talking about.

Care to elaborate?

You know that vibrator thingy they are supposed to use to make sure the concrete and aggregate are all 'consolidated' so as to avoid those voids?

You know, that thingy that, if they even have one, never has a charged battery.

Originally Posted by Jerry Peck

You know that vibrator thingy they are supposed to use to make sure the concrete and aggregate are all 'consolidated' so as to avoid those voids?

You know, that thingy that, if they even have one, never has a charged battery.

Ahhhh, I do know of what you speak, but I have never seen one on a job site. (BTW all I do is residential )

Originally Posted by ben jacks

Sorry to break in...the thingy is called a jitterbug.

Only some types are called that, the rest are all called "vibrators" or "consolidators". But I thought EVERYONE knew that "thingy" was a technical term?

To me this is not a problem
There are 2 types of concrete in this world
- That which has cracked
- And that which will crack

Unless this is a monolithic type of foundation then the slab is not even a structural component of the home.

And unless the crack in the slab is continuously traveling to the foundation wall and then traveles up the foundation wall.

It is only there so your not walking on dirt.

I realize this is an old thread, but it pertains to my situation so I thought I would piggy-back off it. We are building a new home in the Dallas/Fort Worth area and have noticed cracks in the slab. Here's the story:

1. The slab went down about two weeks ago.
2. The framing started about a week and a half ago and is near completion.
3. We noticed the cracks a couple days ago coming from just about every major sewer pipe in the slab.
4. I walked around the other three homes being built is various stages past ours and saw no cracks in those slabs.

I have no experience or knowledge with this sort of thing and don't know what step to take next. People suggest an inspector or structural engineer, but I really don't know how to proceed. Any help or advice would be greatly appreciated. I have attached a few pictures to show what we are dealing with.

Thanks!

From what I can see in the pictures they are shrinkage cracks. Typically caused by any number of factors such as drying out to quick, mixture, etc. Those cracks are common. I don't like it but it's allowed. If the cracks widen or become offset/heave then corrections would be needed.

Originally Posted by Mike Schulz

From what I can see in the pictures they are shrinkage cracks. Typically caused by any number of factors such as drying out to quick, mixture, etc. Those cracks are common. I don't like it but it's allowed. If the cracks widen or become offset/heave then corrections would be needed.

Thanks for the info. I understand shrinkage cracks. They definitely suck, but I know it happens, and I can buy off on these being from that. One bad side of seeing your house being built from scratch I suppose.

Went back out tonight and there are at least 5 new ones from yesterday including one across the length of the patio, one across the entire garage and a few on the main slab. The first one we noticed a week ago has at least doubled in width (it's on the back patio) and increased in length to move to the joint between the patio and the main slab.

So, all in there are at least 12 cracks, and at least 3 that travel the entirety of the slab from back to front and at least two that have increased in width.

to my texas inspectors--do you not require or use floating frames in basements???

cvf

Originally Posted by CHARLIE VAN FLEET

to my texas inspectors--do you not require or use floating frames in basements???

cvf

What is a basement?

Basements are a rarity here. Mostly monolithic slabs on grade with the occasional P & B with crawl space.

jim

we use this here in colorado for slab on grade and basements slabs--i'm sure you have seen them--if not here ya go

cvf

Yes I'm familiar with the floating wall technology... it is that basement thing I don't see much.

Let me get this straight, you guys really dig a hole under the house, on purpose?

Jim's right. We don't see basements in Texas. A few 1950 age homes in Dallas, but we have too much expansive clay soil here.

Those cracks look like typical settlement to me. That's evidence of previous and recent movement. Too significant to be considered "minor", particularly on a new build. Recommend Structural Engineer.

Originally Posted by Robert Slight

Jim's right. We don't see basements in Texas. A few 1950 age homes in Dallas, but we have too much expansive clay soil here.

Those cracks look like typical settlement to me. That's evidence of previous and recent movement. Too significant to be considered "minor", particularly on a new build. Recommend Structural Engineer.

Thank you for your advice. Spoke with the builder this morning who is getting the engineer out to inspect the slab for us. Would it be recommended to hire my own SE as well?

The builder mentioned that with the construction going on he hasn't been able to apply tension to the cables yet (post-tensioned slab). Is this typical to have the frame, exterior walls and roof finished before applying tension?

Also noticed this morning:

1. Crack in garage travels up from the dirt on one side, across the garage and down into the dirt on the other side.
2. Crack on back patio that has widened starts below the dirt on the side of the patio and actually travels to connect to a crack in the living room which then travels to the kitchen and down below the dirt on the front of the slab.
3. There is another one that starts below the dirt on the front, travels into the guest stand-up shower base, then across the guest bathroom and out into the hall, making its way towards the back of the house. This one has increased in length by about 50% in a day...

Like I said before, I know close to nothing about this stuff. I understand what a post-tensioned slab is, but not much more. How likely is it that applying tension at this point will bring these cracks together? Is it possible that applying the tension earlier could have prevented these cracks? My main concerns are the cracks are widening, the number is increasing, the distances are increasing and there are a few that go from below dirt on one side of the slab to below dirt on the other.

Yes, get your own engineer, one that is not beholding to the builder for his income.
There is too little information for us to go on here to give you any meaningful information beyond that.

The tension of the cables adds to the tensil strength of the slab and I would guess that tension should be applied before it is fully loaded but that would require number crunching beyond my expertise.

Cracking of any concrete is NORMAL but there is abnormal (excessive) cracking due to a multitude of factors, all of which should be investigated in order to provide an educated opinion of what is going on with this particular slab.

Also, get yourself an inspector to perform a pre-insulation/drywall phased inspection if you decide to go forward with the process.

Originally Posted by Jim Luttrall

Yes, get your own engineer, one that is not beholding to the builder for his income.
There is too little information for us to go on here to give you any meaningful information beyond that.

The tension of the cables adds to the tensil strength of the slab and I would guess that tension should be applied before it is fully loaded but that would require number crunching beyond my expertise.

Cracking of any concrete is NORMAL but there is abnormal (excessive) cracking due to a multitude of factors, all of which should be investigated in order to provide an educated opinion of what is going on with this particular slab.

Also, get yourself an inspector to perform a pre-insulation/drywall phased inspection if you decide to go forward with the process.

Thanks for the help! I understand it's tough just going by pictures on a forum, but thank you for taking the time to give your feedback.

Originally Posted by Eric Higginbotham

Thanks for the help! I understand it's tough just going by pictures on a forum, but thank you for taking the time to give your feedback.

Stressing of the tendons is supposed to happen within 10 days of the original pour.

This per the Post Tensioning Institute which developed and writes the guidelines for all P-T slabs.

Originally Posted by Nolan Kienitz

Stressing of the tendons is supposed to happen within 10 days of the original pour.

This per the Post Tensioning Institute which developed and writes the guidelines for all P-T slabs.

Yeah, I read that earlier today as well. We are sitting at 14 days since pour with a house nearly ready for drywall and no stressing yet. Not sure how that affects things, but seems like maybe a rush job to get this house up?

EDIT: Another question I have is how stressing the tendons now might affect the frame? If you were to total up the width of each crack that travels north-south on the slab, it would come around, if not more than, an inch of space. If stressing the tendons closed most of that up, how would that affect the structure of the frame, if at all?

If I saw the cracks in the first post, I would not be concerned. I actually would be surprised if I didn't see at least one crack like that. Those crack occur due to movement and shrinkage. I get concerned if the crack is showing vertical displacement or chunks are popping loose due to movement.

As to the cracks showing up in a slab that is only a few months old, it is not unusual for them to show up a few days or weeks. In fact most of the cracking will show as the main curing of the concrete occurs (which in in the first 54 days).

Ted, you need to keep in mind that you are accustomed to post tension slabs in Texas. I am familiar with them as I built several hundred homes in San Antonio. Post tension slabs are a whole different monster. They have positive reinforcement due to the tension on the cables. In this area, we just use rebar which is a metal rod that just lays there and binds to the concrete to help hold it together (assuming that it was properly installed in the first place). This allows considerably more cracking to occur than you typically see in post tension. In many cases they no longer use the wire mesh either, just the fiber reinforcement. The more stable soils here do not require the positive reinforcement from post tension.

As to compaction under the slab, I have never seen a slab that was truly compacted the way it should be. Typically the stem wall is constructed and the grading contractor back fills it. He often "compacts" the soil by running the bobcat over it. If they actually use a compactor and get the soil the way it should be everything is great...until the plumber gets there to run the drains and water lines. The soil is then raked back into the trenches and they get ready to pour the slab. All that compaction is lost.

One last item to address, the vibrator for the concrete. At one company I worked for we made the concrete contractor use them to consolidate the concrete around the post tension cables. They also tried to use them to pull the concrete down into the middle of the slab. Many of the contractors would run the vibrator far to long which actually made things worse. If not used properly, the vibrator will separate the aggregate from the cement and make it weaker. That is why many of the engineers I have worked with did not want them used on the slabs. There is too much of a good thing.