Author Topic: Footings 101  (Read 529 times)

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Offline retiredmarine

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Footings 101
« on: April 11, 2018, 01:17:09 AM »
The frost line in my area is 24", my question is if in the course of site preparation you remove 10" of soil does that mean your footing depth need only be 14" on the new pad?  I'd also like to hear any economical ideas for sealing the first 2-4 rows of block that will end up being back filled against - crawlspace, no basement.

Offline Don_P

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Re: Footings 101
« Reply #1 on: April 11, 2018, 02:41:58 AM »
The bottom of the footing needs to be at least 24" below final exterior grade. It sounds like the interior may be lower, run perforated drain around the outside of the footing on landscape fabric and cover with clean gravel then wrap the fabric over the top of the gravel before the soil backfill... a gravel sausage around the perf tube. The fabric helps keep soil out of the drain. Slope the drain to daylight. I also ran a drain out of the crawl, gravel and a thin slab 2-3" thick, much nicer and drier under there. A mortar parge coat and foundation tar below grade works well for damproofing. As you break out of grade a double parge coat will hide the mortar joints between blocks that you often see telegraph through when someone parges block, a scratch coat then a final coat. I prefer to damp sponge that final coat. Getting into taste on all that though.

Offline retiredmarine

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Re: Footings 101
« Reply #2 on: April 11, 2018, 05:31:06 AM »
Thanks Don!  Anyone have any experience or an opinion on formless footing pouring - using the footing trench its self act as the form?

Offline Don_P

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Re: Footings 101
« Reply #3 on: April 11, 2018, 02:03:21 PM »
Yup, very common here, we have soils that hold up well. Use a square point shovel to clean and square up the trench. It puts the foundation drain on top of rather than beside the footing but that has worked fine here. On a wetter site it is better to get the drain down at footing bottom elevation.

Offline retiredmarine

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Re: Footings 101
« Reply #4 on: April 13, 2018, 07:18:14 AM »
Thanks Don.  Where are you located at again?

Offline Don_P

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Re: Footings 101
« Reply #5 on: April 13, 2018, 02:26:59 PM »
I'm in southwestern VA, the Blue Ridge, yourself?

Offline retiredmarine

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Re: Footings 101
« Reply #6 on: April 16, 2018, 04:10:45 AM »
Looking to build in Southern Missouri near Rolla.  That is if I can get out of the DC area!!  So what's your thoughts on folks that install the vertical rebar by pounding them in to the ground to tie their footings in with their block wall.  I've seen comments about eventual rust and some that don't seem to care. thoughts?
« Last Edit: April 16, 2018, 04:35:44 AM by retiredmarine »

Offline MountainDon

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Re: Footings 101
« Reply #7 on: April 16, 2018, 05:40:42 AM »
As with anything, there are always people who don't care about possible consequences. When rebar is pounded into the ground and concrete poured around it, the rebar can rust and the rusting can extend up into the concrete. The corrosion byproducts, rust, reduces tensile strength and has greater volume, which can lead to cracking. A vicious circle is started with more corrosion, more cracks, loss of strength.

When rebar is encased by at least 2 inches of good dense concrete the rebar is protected. Good concrete has a pH of about 13. That causes the steel to form a protective passivating layer. The passivating layer actually does not stop corrosion but it slows corrosion to an insignificant rate. A rebar end exposed in the earth can corrode over 1000 times faster depending on soil type.

Reference one, and reference two
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline retiredmarine

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Re: Footings 101
« Reply #8 on: April 16, 2018, 06:25:14 AM »
I KNEW the side you were going to be on lol.  I think your right, it may be more convenient but why do something that you know will result in damage later.

 

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