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re: Post Tension Slab
Posted on 3/7/15 at 9:56 pm to stout
Posted on 3/7/15 at 9:56 pm to stout
USDA says sandy loam soil in my area. Sounds as if a normal slab will work since that is what is typically installed but the dirt work is critical. Is there a certain time you need to wait after the dirt work is done before pouring slab?
1
Posted on 3/7/15 at 9:56 pm to ags01
quote:
Penetrate them 5' in the rock and you're golden
They are adding onto an overpass here and I wish I knew how many and how tall the pylons are they have been putting in. Literally whole trees and hundreds of them a few feet apart. It's an interesting process to me.
This post was edited on 3/7/15 at 10:06 pm
Posted on 3/7/15 at 10:00 pm to ags01
quote:
Posted by ags01
It's intersting that what we here in Texas call gumbo soil is clay that may have a PI as high as 60. That shite is worthless here. I guess in Louisiana where a clay subgrade might stay consistently saturated, the effect of its expansive qualities would be diminished.
Yep, the atterberg limits for soil in the New Orleans would normally raise serious expansive soil flags, but it can never really dry out.
There is some expansive soil in areas on the Northshore.
Posted on 3/7/15 at 10:05 pm to daviddsims
quote:
Is there a certain time you need to wait after the dirt work is done before pouring slab?
I usually start a day or two later but I trust my dirt guy. You can let it sit and settle some but the bad thing is that if you get in a rainy season you can have a lot of run-off. The dirt you dig out of your footings will probably make up for it though and if not just get some sand to get your grade.
Also, I am not sure how long a compaction test will be good for if you let it sit for a while after the pad prep work. Maybe someone else would know that but you would also need to see if letting it sit would reduce his liability somehow.
Posted on 3/7/15 at 10:12 pm to stout
It's a fine line, compaction and optimum moisture. If allowed to sit too long, moisture would fall below optimum and it is hard to regain without ripping and starting all over.
Posted on 3/7/15 at 10:19 pm to ags01
Yep and people have always been told to let it sit to get rain to compact more. I have seen whole parts of pads cave in while footings were being dug because it had too much moisture from sitting and lost its compaction.
If the people doing the prep work do it correctly and build it up layer by layer, you should be fine to start right away. Again, I have seen people move around huge chunks of dirt instead of building it up. You aren't going to get good compaction doing that.
If the people doing the prep work do it correctly and build it up layer by layer, you should be fine to start right away. Again, I have seen people move around huge chunks of dirt instead of building it up. You aren't going to get good compaction doing that.
Posted on 3/7/15 at 10:22 pm to daviddsims
we have some major problems with foundation problems due to expansive soils here in my area and I just can't understand why post tension slabs are not used more frequently...
as the others say, the main thing is to be sure your dirtpad is thick enough and has the right compatction...also, require that the pad extend out 6-10 feet past the edge of your slab...you want your house to be on a little plateau of good and properly packed dirt, imo...
fwiw, if I were building a house, I would both ensure that the dirt was more than adequate and also consider post tension slab....this constant worry about foundation problems is just not my thing...
as the others say, the main thing is to be sure your dirtpad is thick enough and has the right compatction...also, require that the pad extend out 6-10 feet past the edge of your slab...you want your house to be on a little plateau of good and properly packed dirt, imo...
fwiw, if I were building a house, I would both ensure that the dirt was more than adequate and also consider post tension slab....this constant worry about foundation problems is just not my thing...
Posted on 3/7/15 at 10:29 pm to daviddsims
Clay, compaction test, PT.
A good dirt man is key. Putting PT without proper prep work is still asking for trouble.
A real compaction test doesn't cost that much, but a lot folks skip that step.
A good dirt man is key. Putting PT without proper prep work is still asking for trouble.
A real compaction test doesn't cost that much, but a lot folks skip that step.
Posted on 3/7/15 at 10:32 pm to Spankum
PT slabs aren't a silver bullet for expansive soils. It could be bad enough that you need to remove/replace soil or build on void forms.
Posted on 3/7/15 at 10:39 pm to ags01
quote:
Clay is an extremely expansive material and tears slabs apart in Texas. This is precisely why post tension is used. Clay is hauled out and replaced with a low PI material such as sand or crusher fines.
houses arent built on lean clays?
Posted on 3/7/15 at 10:44 pm to ags01
quote:
It's intersting that what we here in Texas call gumbo soil is clay that may have a PI as high as 60.
it gets higher than that
quote:
I guess in Louisiana where a clay subgrade might stay consistently saturated, the effect of its expansive qualities would be diminished.
unless you are south of I10, the topsoil will be dried and dessicated
Posted on 3/7/15 at 11:28 pm to daviddsims
House snobs on here talk down on DSLD, but they are doing post tension in all of their slabs in SE LA. Maybe they are ahead of the game
Posted on 3/7/15 at 11:38 pm to TigerTatorTots
DSLD continues to move upmarket.
Their houses compare very favorably with some of "dog and pickup" guys that build 7-8 houses per year. A lot of the smaller guys need to up their game, quality-wise. They build a 400K house they same way they used to build a 200K house.
Just my opinion.
Their houses compare very favorably with some of "dog and pickup" guys that build 7-8 houses per year. A lot of the smaller guys need to up their game, quality-wise. They build a 400K house they same way they used to build a 200K house.
Just my opinion.
Posted on 3/8/15 at 12:41 am to daviddsims
Considering the workmanship of some PT companies can be as poor as other trades in the residential market I would spend the same money on upgrading rebar thickness (eg #4 typ to #5), footing thickness, and concrete psi, and possibly small shaft piles at major load bearing points.
Posted on 3/8/15 at 3:41 am to TigerTatorTots
quote:
House snobs on here talk down on DSLD, but they are doing post tension in all of their slabs in SE LA. Maybe they are ahead of the game
I just watched a developer (DSLD) build up a subdivision 8 feet in elevation without a single compaction device onsite for 3 years. I watched them pour a slab late in the day we got down to the low 20's that night.
They are putting in PT slabs to try and get through the 10 year warranty period and as a marketing tool. I guess if the slab stays together as the entire home sinks and tilts over the next 20 years that is a good thing?
I wouldn't call that quality construction but some may.
When you buy a house from a tract developer you are getting the lowest common denominator in materials, labor, supervision (or lack thereof), and design.
For most, these won't be permanent homes. But I pity the poor bastard who ends up with the note 20 years from now and has a POS that needs tens of thousands in repairs due to shoddy construction materials and methods.
Posted on 3/8/15 at 7:07 am to AndyCBR
quote:
Considering the workmanship of some PT companies can be as poor as other trades in the residential market I would spend the same money on upgrading rebar thickness (eg #4 typ to #5), footing thickness, and concrete psi, and possibly small shaft piles at major load bearing points.
This right here, but also, increase the slab thickness.
Posted on 3/8/15 at 7:37 am to daviddsims
Just go with rebar but pay extra to put polypropylene fiber in your concrete. You could even pay for structural fiber if you are that worried.
Posted on 3/8/15 at 8:41 am to Grouper Picatta
As others have said, if you go PTS:
1. Hire an engineer to do a site specific engineered PTS design taking into account the underlying soils condition discovered through a site specific soils test. Do not let the builder or foundation designer design their plan based on some generic USDA agricultural map or how other homes were designed down the street in the same neighborhood.
Here is some additional advice that was given to me for building a home in La.:
2. Be cautious with landscaping near the house and watering system in the event you have expansive clays.
3. Be careful building immediately after trees have been cut removed from or adjacent to property as that may affect the soil equilibrium
4. Make sure all contractors and sub consultants who design or work on your house are licensed and insured.
1. Hire an engineer to do a site specific engineered PTS design taking into account the underlying soils condition discovered through a site specific soils test. Do not let the builder or foundation designer design their plan based on some generic USDA agricultural map or how other homes were designed down the street in the same neighborhood.
Here is some additional advice that was given to me for building a home in La.:
2. Be cautious with landscaping near the house and watering system in the event you have expansive clays.
3. Be careful building immediately after trees have been cut removed from or adjacent to property as that may affect the soil equilibrium
4. Make sure all contractors and sub consultants who design or work on your house are licensed and insured.
Posted on 3/8/15 at 8:42 am to AndyCBR
That's another concern here, not many companies that do PT so the likelihood of a poor job is pretty high.
Posted on 3/8/15 at 8:45 am to daviddsims
I work for an Architect and we stopped providing foundation plans with our house plans a couple years ago due to the homeowners not wanting to take the proper measures when dealing with their dirt and slab. If it's not "pretty" they don't care to spend money I guess. On both our plan notes and contract it specifically states engineers soil reports and compaction tests must be provided before we supply a foundation plan. 95% of the time they opt out and do PT. PT slabs I believe are running about $1.00 sqft extra. To me that's a small price to pay to have extra piece of mind.
If you use a PT company, they have an engineers stamped set of drawings that they go off of, or should if they are worth a shite. If failure does occur, that gives you more protection in case you have to file a lawsuit. I've personally seen this twice now in the last couple years and it's worked out in the homeowners favor.
Just my .02. Good luck.
If you use a PT company, they have an engineers stamped set of drawings that they go off of, or should if they are worth a shite. If failure does occur, that gives you more protection in case you have to file a lawsuit. I've personally seen this twice now in the last couple years and it's worked out in the homeowners favor.
Just my .02. Good luck.
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