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Old 01-05-2012, 01:57 PM   #1
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slab thickness


I am trying to cut a hole in the houses slab for some drain pipe to be put in, right now I am no where near the footer and the slab is 9 inches thick it appears... is this normal? everything I read says a houses slab is usually 4" thick and the footers are thicker.. it appears they poured the footers, laid the block then brought the slab up to the almost top of the first course of block, because I can just see the top of it on the permitier of the slab...


making cutting a pain in the ......

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Old 01-05-2012, 02:10 PM   #2
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slab thickness


How do you know you aren't cutting over the top of an interior concrete beam?

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Old 01-05-2012, 02:41 PM   #3
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Might be just a thick spot---or you could be at the house I helped build where the contractor poured a 14" thick slab just to keep a job on schedule---
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Old 01-05-2012, 02:48 PM   #4
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How do you know you aren't cutting over the top of an interior concrete beam?
going by the plans for the house construction, there should be nothing under this section
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Old 01-05-2012, 02:50 PM   #5
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slab thickness


"Proposal Plans" or "As-Built Plans"?
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Old 01-05-2012, 02:52 PM   #6
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"Proposal Plans" or "As-Built Plans"?
these are the plans the builders used, so I'd assume built plans, I also have a copy of the set turned into the building department they are marked as "proposed" the others are slightly different but still nothing in the area i'm at
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Old 01-05-2012, 02:59 PM   #7
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slab thickness


Don't know but plans are not always totally reliable when it comes to where underground improvements are installed.

Assuming you are ultimately doing a trench...
Move down line and cut there and see what you find.
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Old 01-05-2012, 03:17 PM   #8
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slab thickness


Did your plans state the thickness of the slab? A 9 inch thick slab is unusual for residential, in my experience 4 inches is pretty common. You do not state where you are, there are parts of the country where thick, prestressed slabs are commonly built, you had best make sure you do not have one of those, cutting through a prestressing tendon would make for a very bad day for you.
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Old 01-05-2012, 03:25 PM   #9
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Did your plans state the thickness of the slab? A 9 inch thick slab is unusual for residential, in my experience 4 inches is pretty common. You do not state where you are, there are parts of the country where thick, prestressed slabs are commonly built, you had best make sure you do not have one of those, cutting through a prestressing tendon would make for a very bad day for you.
Good point!

It could also be a "post-tension" slab.
Any signs of that around the exterior of the slab?
Where are you and how old is this slab?
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Old 01-05-2012, 03:30 PM   #10
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Good point!

It could also be a "post-tension" slab.
Any signs of that around the exterior of the slab?
Where are you and how old is this slab?
I'm in western pennsylvania, the house was built in 1997

Cutting through this is extreamly hard, never saw concrete this hard to cut through..

got about 3 ft down the line now and its pretty much a consistant 8-9 ish inches...

where there is a shrink gap near the wall I can push a metal wire about 9 inches down until it hits the footers, and you can feel it hit... haven't hit any rebar or wire mesh, but it did have the plasic vapor barrier under it before the gravel
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Old 01-05-2012, 03:31 PM   #11
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slab thickness


Is it not possible to get a "sonar" device to find out the profile of your slab? I saw a concrete company "ping" a slab to determine that it was sound (no pun intended) and assumed it was some kind of sonar deal... or maybe just showmanship to make the owner think somebody did something.
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Old 01-05-2012, 03:52 PM   #12
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slab thickness


4" is the minimum thickness for a slab, they typically can vary within the 4"-5" range if the backfill was properly graded.. in your situation its possible the guys who did the foundation work didnt allow for the correct amount of 3/4 stone to backfill with so there is a large section which is thicker than the rest. could be do to a severaly out of level footing too so they had to create a level slab.. the footing being out of level isnt a big deal it just made things harder for the guys doing hte actual foundation wall, the slab finishers and the framers... as long as everything is structurally sound,, you only stress will be cutting out the extra thick concrete
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Old 01-05-2012, 04:44 PM   #13
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slab thickness


Is this in the basement of a home where they may have poured monalific footing/slab for lally columns?
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Old 01-05-2012, 06:01 PM   #14
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Is this in the basement of a home where they may have poured monalific footing/slab for lally columns?
monolithic footings? you mean like the entire slab is a footing? if thats what you mean, it does have independent footings going by the design specs, and the block on the outside walls go at least 1 course below the slab grade, you can see the top maybe 1/2" of the first course from inside the basement. its shown being built like this in the building plans

http://www.infoforbuilding.com/basementfoundation.gif

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Old 01-05-2012, 06:34 PM   #15
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slab thickness


Are you cutting close to a lally column?

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