Gap under post-tension slab?
- Thread starter hal1
- Start date
wssix99
Well-known member
Did a building inspector tell you that???
COSMOS
Well-known member
Last edited:
wssix99
Well-known member
... ^ it's not always like that anymore.
Even if you believe that 99 out of 100 inspectors are happy to lend a hand and stand up for prospective owners outside of a scheduled inspection, the risk of running into that one can have a devastating impact.
If the OP reaches under the slab and finds that the void actually goes back more than a few inches or that there is a family of Diamondbacks living in there now, (maybe a stick would be a good idea...) then their original salesman probably has the most leverage over the situation. (To them - the customer is always right and they will want everything to go smoothly to close so they can get their commission.)
Even if you believe that 99 out of 100 inspectors are happy to lend a hand and stand up for prospective owners outside of a scheduled inspection, the risk of running into that one can have a devastating impact.
If the OP reaches under the slab and finds that the void actually goes back more than a few inches or that there is a family of Diamondbacks living in there now, (maybe a stick would be a good idea...) then their original salesman probably has the most leverage over the situation. (To them - the customer is always right and they will want everything to go smoothly to close so they can get their commission.)
Last edited:
DPG
Well-known member
OP - The problem is minor. The PT slab is not going anywhere and it is doubtful that it will be a structural problem. It is just not a big area. Go and politely ask the super to fill the void with concrete the next time that they have a pour scheduled. He already knows that you are aware of it and he will want the problem (you) to go away. He is also probably dreading having you watch over every step of your new home construction since you are already over analyzing / blowing this out of proportion.
I don't think the slab is going to sink or shift, my only concern is that this corner could crack due to not having anything under it to support it. I don't know construction so maybe this is something that just doesn't happen. I do know that I don't think there should be a gap under the porch-but maybe I'm wrong on that too.
The only thing I may be blowing out of proportion (to them) is that I want them to do exactly what you have mentioned. I'd be thrilled if they'd fill the void with concrete. The superintendent said they will fill it with dirt! - And now I don't even think they did that
So I went back today. It looks like they doing some preliminary smoothing of the yard, and simply covered up the hole. I don't think the super got around to doing anything . When I push a piece of rebar into that space, it goes in smoothly with no resistance. Similarly, when I press my foot at that spot it sinks down and seems to just be pushing dirt in to that gap - once again, no resistance.
EDIT: To clarify, it doesn't seem they covered the gap to hide anything, it just looks like the whole yard was smoothed over by the guys doing their work getting ready for the next step
Last edited:
1949 caddyman
Well-known member
We have expansive soil in Arizona. It can move when wet. It can crack footer type foundations. The fix for this as I understand it is the post tension slab. The ones I have seen are 6" thick & then the cables are pulled hydraulicly to strengthen the slab. I don't think it matters if there is a void as that is the true of thing the post tension is made for. IMO.
https://en.m.wikipedia.org/wiki/Expansive_clay
https://en.m.wikipedia.org/wiki/Expansive_clay
FordTruckWench
Well-known member
Scrape out a small hole. Stick a camera (i.e. smart phone) in the hole and take a picture of the gap. The phone can fit where your head can't. This also gives you a record of the problem.
This is what they're telling me, that the integrity of the slab is intact. And yes, that is the answer I was fishing here for. But as you can see, I'm getting opinions on both sides here.
COSMOS
Well-known member
The expansive soils question, keep reading on that one lots of opinions about it in the Geo-tech industry here in the valley. Been in on my share of them between the Geo-tech engineers, the dirt guys, structural engineers and the concrete finishers......
Last edited:
Zeke
Well-known member
Inspectors are neutral and objective. If it meets code but the workmanship is not very good, it passes. IOW, if all the nailing and attachments are in a framed wall, but it's not absolutely straight, it passes framing inspection.
What constitutes 'straight' in one man's eyes vs. another is the subjective part. Inspectors don't get involved with that. They are not there to protect the owner from the 'unscrupulous contractor'. They could give a **** less about the owner. In fact, they are working with the contractor to ensure code compliance, that's all. And they will be working with that contractor again and again. It becomes a relationship after time.
Not so with owners unless they are inspecting an owner/builder project. There again, they are there to see about the 'builder' part. The fact that the owner is doing the project himself has nothing to do with it. Actually, inspectors may be a bit more leery of O/B projects.
What constitutes 'straight' in one man's eyes vs. another is the subjective part. Inspectors don't get involved with that. They are not there to protect the owner from the 'unscrupulous contractor'. They could give a **** less about the owner. In fact, they are working with the contractor to ensure code compliance, that's all. And they will be working with that contractor again and again. It becomes a relationship after time.
Not so with owners unless they are inspecting an owner/builder project. There again, they are there to see about the 'builder' part. The fact that the owner is doing the project himself has nothing to do with it. Actually, inspectors may be a bit more leery of O/B projects.
I want to thank everyone for their help. It seems that while there is only one right way to do this, there are other, not wrong ways also. It seems this come close to bringing this to an end
When I spoke to an SE on the phone, he said that yes, a post-tension slab is designed to span gaps that may eventually occur, but that the slab should at least start out on a solid base.
After sending him some pictures, here is the response I got from him, - Notice at the end, after his suggestion, he still seems to defer to the original designer, as he suggests "that the geotechnical and/or structural Engineer of Record involved with the original project design provide recommendations for that condition prior to you moving into the home."
"Hi Harlan,
Yes, that sounds like what you were describing over the phone. Based on the pictures I would expect the contractor to fill in that space below the slab (perhaps a concrete slurry), so as to provide full bearing below the foundation. However, I would like suggest that the geotechnical and/or structural Engineer of Record involved with the original project design provide recommendations for that condition prior to you moving into the home.
Thank you,
John Doe, SE
XXXXXX Engineering Consultants, LLC
XXXXX N. ##nd Street, Suite ***
Phoenix, Arizona 85xxx
When I spoke to an SE on the phone, he said that yes, a post-tension slab is designed to span gaps that may eventually occur, but that the slab should at least start out on a solid base.
After sending him some pictures, here is the response I got from him, - Notice at the end, after his suggestion, he still seems to defer to the original designer, as he suggests "that the geotechnical and/or structural Engineer of Record involved with the original project design provide recommendations for that condition prior to you moving into the home."
"Hi Harlan,
Yes, that sounds like what you were describing over the phone. Based on the pictures I would expect the contractor to fill in that space below the slab (perhaps a concrete slurry), so as to provide full bearing below the foundation. However, I would like suggest that the geotechnical and/or structural Engineer of Record involved with the original project design provide recommendations for that condition prior to you moving into the home.
Thank you,
John Doe, SE
XXXXXX Engineering Consultants, LLC
XXXXX N. ##nd Street, Suite ***
Phoenix, Arizona 85xxx
Last edited:
Zeke
Well-known member
My personal experience with engineers is that the first thing the do is cover their ***. Always over the top recommendations. YMMV.
ishiboo
Well-known member
IMO, this is not a big deal unless it's a much larger area than we are seeing. Post-tensioned slabs act more like a single unit than a regular slab, which requires support under it as it easily cracks in the "shear" with a void underneath. And it's from the spillage. Pack it with some gravel and it's done.
Not to say the prep work is irrelevant, but one of the points of the system is it's much better acting as one single piece to float on less-than-perfect sub grades.
Not to say the prep work is irrelevant, but one of the points of the system is it's much better acting as one single piece to float on less-than-perfect sub grades.
But is packing it with gravel really better than doing nothing? I can't see 'packing' with anything really offering an additional support. That notwithstanding, the other observations you're making about the post-tension slab is what the builder and some others are stating
Last edited:
cat06
Well-known member
your gonna think this is crazy, but fill it with closed cell foam
COSMOS
Well-known member
The void needs to filled with a one bag/slurry mix no way around it. Moisture/water from rain and landscape watering from will eventually collapse the void and sewer trench more over time if it is not done (figured I'd leave this for last the long term real issue).
Take a garden hose and soak the sewer trench with water for about 20 minutes come back the next day and then say the void does not need to be filled. hal1, did you ever pick up a piece of rebar and shove it into the ground near the sewer cleanouts and into the void like I had suggested.?
Take a garden hose and soak the sewer trench with water for about 20 minutes come back the next day and then say the void does not need to be filled. hal1, did you ever pick up a piece of rebar and shove it into the ground near the sewer cleanouts and into the void like I had suggested.?
Sorry, I missed that. Yes, the earth is solid everywhere, even just outside where that opening is just inches along the perimeter of the slab.
wssix99
Well-known member
This is not the case.
Risking causing even more panic here.... there are probably other voids under the house as we speak. That's what happens with expansive soils - they also contract. After the pour, there could have been movement in other areas.
^ This is what the post-tensioning is for. It holds the house/slab together as the whole thing heaves and as localized voids may form underneath.
How about this for a confidence builder? Just go stand on the area with a few people and jump up and down? If it cracks - then the contractor can cut the thing out and repour it now during construction. If not - it's only going to get stronger as the concrete cures and hardens over time.
COSMOS
Well-known member
The highlighted above comes from one most innovative companies here in the valley, somewhere around 30+ years is he wrong also.?
wssix99
Well-known member
That's such a ridiculous solution to this "problem," that I'm sure the processional who said that didn't understand the true context of what they were commenting on. I can't imagine that a professional would recommend "mudjacking" if they were to see the pictures in this thread.
As was pointed out earlier in the thread, engineers will always defer to the CYA game and it's really easy for them to suggest a $1000 solution to a $15. It's not their money!
I've had a number of situations like this building my own house. The path of least resistance here is probably to go to the local home store, get a 5 gallon bucket, a shovel, two bags of concrete, a few gallons of water, and a case of beer:
- Go over to the site after 5:00, dig up the dirt, mix up the concrete, and fill it one's self.
- If any one "official" comes buy and acts difficult - give them the case of beer to go away. (If no-one comes - keep the case as a personal bonus.)
^ Yes, this is a little bit of time and effort, but it will be much less time and effort than trying to chase down other people and/or pay professionals to take care of this.
COSMOS
Well-known member
That's such a ridiculous solution to this "problem," that I'm sure the processional who said that didn't understand the true context of what they were commenting on. I can't imagine that a professional would recommend "mudjacking" if they were to see the pictures in this thread.
As was pointed out earlier in the thread, engineers will always defer to the CYA game and it's really easy for them to suggest a $1000 solution to a $15. It's not their money!
I've had a number of situations like this building my own house. The path of least resistance here is probably to go to the local home store, get a 5 gallon bucket, a shovel, two bags of concrete, a few gallons of water, and a case of beer:
- Go over to the site after 5:00, dig up the dirt, mix up the concrete, and fill it one's self.
- If any one "official" comes buy and acts difficult - give them the case of beer to go away. (If no-one comes - keep the case as a personal bonus.)
^ Yes, this is a little bit of time and effort, but it will be much less time and effort than trying to chase down other people and/or pay professionals to take care of this.
Duh, skip the one above did ya...
Last edited:
Okay, so there's pretty much a consensus on the right way to do things. But what I don't understand is this... how does packing cement underneath the porch section of the slab provide any weight bearing support. In other words, how do you fill a gap where at the end there's actually upward pressure on the slab above it?, would there ever really be any direct support of the slab above it?
It's because of the lawyers.
wssix99
Well-known member
The idea is to get solid, uncompressible material between the concrete and the "solid" undisturbed earth.
That undisturbed/excavated earth provides the support for your entire house. (In the middle of your house, you have some compacted gravel fill that transfers loads to the earth below.) That being said, the ground in your area isn't the best support, which is why you have a post-tensioned slab.
For the area that you want to fill, it's very difficult to compact dirt in that space well. It's less difficult to compact gravel in that space. Cement is great, because you don't need to compact it - it will form a solid mass as long as you rod it to get rid of the air pockets.
Is your concern that the earth below is relatively "soft?"
Pettydev
Member
You shouldn't worry about this. A few things to note:
1) this is a post tension slab. I worked for a large builder in Arizona in the past where two post tension slabs were poured with an incorrect setback from the lot lines and had to be removed. It took a 20 ton track hoe two weeks to break the slabs apart and load in a dump truck. They even broke a 4cy bucket off of the machine in the process. Literally, every time they picked up a corner of the slab in an attempt to break a piece off, the entire slab held together in one monolithic piece. That's how a post tensioned slab is supposed to work, and I've seen first hand that they do.
2) This is your porch. Most builders actually leave this pour until last when they pour the driveway and walkways. In your case, and mainly due to the nature of your floor plan, Taylor Morrison decided to integrate it into the slab pour. The point is, you have a way over-reinforced patio.
*for what it is worth, I have a construction degree and grew up in Phoenix. Worked for big builders in Phoenix. I literally focused on residential construction in AZ. I mention this only to reassure you that my opinion (for what it's worth) is you have nothing to worry about in regards to your slab.
1) this is a post tension slab. I worked for a large builder in Arizona in the past where two post tension slabs were poured with an incorrect setback from the lot lines and had to be removed. It took a 20 ton track hoe two weeks to break the slabs apart and load in a dump truck. They even broke a 4cy bucket off of the machine in the process. Literally, every time they picked up a corner of the slab in an attempt to break a piece off, the entire slab held together in one monolithic piece. That's how a post tensioned slab is supposed to work, and I've seen first hand that they do.
2) This is your porch. Most builders actually leave this pour until last when they pour the driveway and walkways. In your case, and mainly due to the nature of your floor plan, Taylor Morrison decided to integrate it into the slab pour. The point is, you have a way over-reinforced patio.
*for what it is worth, I have a construction degree and grew up in Phoenix. Worked for big builders in Phoenix. I literally focused on residential construction in AZ. I mention this only to reassure you that my opinion (for what it's worth) is you have nothing to worry about in regards to your slab.
Bruce4310TX
Well-known member
Post tension are a Joke.....builders use it because it saves the cost of re-bar and the labor to install it. Here in Texas the land of millions of failed post-tension slabs you can make a nice living jacking up broken PT-Slabs. That slab will crack and if it cracks there the cables will not be able to hold it without support under it. The void must be filled. Re-bar slabs with the proper footing is the only way to do it. Remember all concrete cracks only re-bar holds it together, fix it now or run from it. Or pay dearly down the road.
COSMOS
Well-known member
It's obvious in this video why this post tension slab failed, at least to me it is...
Last edited:
wssix99
Well-known member
God help us. Zombie concrete threads are waking from the dead all over the place.