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The concrete deck on my build-in-1937 house seems to be falling apart from the bottom. The deck itself is a 4.5 inch slab connected to the front of a brick house, and by two brick pillars in the corners. Someone added another cinderblock pillar in the middle of the falling apart area (pictured), and tried to patch the damage, but most of the patch has fallen away. (There's wiring indicating an AC compressor used to reside under the deck.) The falling apart area is deep enough in parts to expose whatever 1930s rebar looks like, which is flaking away. Pictured is the worst part, where it's more than an inch deep.

This looks like more than a simple patch I could cover with epoxy. Does anyone have any advice on how I should proceed? Can I recover this with new cement? I'm worried (without any actual evidence) that the edge of the deck may not be as stable as it looks from the top!

enter image description here

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  • At this age there can be multiple issues, first concrete continues to get harder over the decades and becomes extremely brittle, if one side of the deck support is settling it will break like glass, if there is some steel rebar the rebar will help support it even if cracking. I have not seen any patching that will stop the but sealing the top so no water can get in the cracks in the winter may extend the life, with the rebar and only being an inch deep crack sealing top and bottom may be the best bet , I leave this as a comment because I don’t know your local weather or soil conditions. – Ed Beal Feb 8 '20 at 21:47
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    Concrete fails easiest in tension and whatever you do from underneath will be in tension. The best solution is to redo the slab. – Solar Mike Feb 8 '20 at 21:49
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    that looks structurally unsound, probably the the cheapest way to fix it is to rip it out and build a new deck platform – Jasen Feb 8 '20 at 23:35
  • Agreed, any answer will not be good news or an easy fix.... – Jack Feb 9 '20 at 3:16
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Water penetrates the concrete and rusts the rebar which then expands and cracks the concrete. It's an age-old problem and considering the age of this slab, its lifetime is over.

From the looks of the photos, it's severely compromised and should be removed immediately.

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  • Thanks, I'm already pretty scared! – Davide Feb 9 '20 at 23:39
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Yep...the slab is failing and the brick wall looks like it’s failing in a couple areas too. Fortunately you’ve seen the decay and can take action by replacing the slab and fixing the wall.

You’ll need to fix the brick wall by removing the loose bricks, insuring the wall is adequately reinforced, and provide adequate reinforcing bars between the slab and wall. (I think the CMU wall could use some minor pointing too.)

In fact, I’d bet that slab was originally poured on backfill and was not a structural above ground slab, because: 1) the bottom of the slab is rough, like it was poured on dirt not formwork, 2) original wall was brick and CMU wall added later to reduce the span of the slab, 3) the area was probably dug out when the ac compressor (and CMU wall) was added...although heat pumps had been invented before your 1937 House was built, the split system heat pumps were not widely used, 4) the slab is only 4 1/2” thick. Technically a 4 1/2” structural slab could span that far nowadays, back then a 4 1/2” slab would have been a slab on grade.

You cannot “fix” the existing slab by patching the bottom. At a minimum, it would take a completely new reinforced slab.

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  • Thanks! Based on the neighborhood, all the houses have these giant unsupported concrete spans. Ours appears to be the only one with the CMU bit. Clearly the deck was already falling in on a previous owner. – Davide Feb 9 '20 at 23:40

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