DYI 1900’s concrete slab porch sag/crack
Hi –
This is a DIY problem that might turn into a contractor project.
I have a circa 1900 row house (unit 2). This is in central NJ so we have snow and freezing temps in the winter, and summers reach to 100f. Each house is two stories and a basement. We share a concrete porch with unit-1 as shown on the diagram. This concrete porch is a slab which is supported by the concrete foundations and a steel beam in the basement of each unit. Each unit has wooden framing that rests on the slab.
There was a crack in the slab (see diagram) and we had several contractors come out, inspect it and give estimates. Estimates ranged from $600 (we’ll patch it right up) to $15,000 (cut the slab, build a new form, ….). I didn’t trust the low estimates – I wanted a structural solution, not a cosmetic one. The high estimate sure seemed extreme to me, and I couldn’t afford it anyway.
I repaired the crack in the slab at point (D), which turned out to be totally separated, using an Abatron product. As it turned out there was also a crack in my foundation at point (E) which ran from the steel beam diagonally downwards to my door (underneath the slab). Closer inspection showed that it was totally seperated as well, and it was also repaired with the Abatran epoxy/cement. The repairs using the Abatron epoxy are quite solid and worked well (about $300).
The concrete slab is also supported by an outside wall (points C to D) of CMU blocks – this was built about 12 years ago when the original concrete wall collapsed. The mix between the top CMU course and the bottom of the slab had disintegrated, so I replaced it with new masonary mix and then coated the outside of the CMU’s with masonary coating (to provide protection from water, snow, and freeze/thaw problems).
So we moved everything off of the slab porch so we could coat it with waterproofer (to help prevent further problems), and I noticed that the slab didn’t appear level…
So I looked at several of the other units (there are 10 or so in total) and from observation have deduced the following:
(1) The slab is highest at point (A) and low at point (B).
(2) The slab should be resting on the shared concrete foundation – it isn’t.
(3) The slab has been “repaired” before, and it was jacked up at point (A), which is what raised the slab off of the foundation.
(4) Point (B) is low and is actually level with point (E).
(5) The slab is warped and cracking at point (E) due to the stresses.
So here’s what I was thinking
(1) Jack up the steel beam at point (B) so that the slab is level to point (A).
(2) Fill the void between the slab and the foundation wall with masonary cement, to help support the slab.
Will this work? Are then any serious drawbacks for a DIY’er? Should I call in a pro?
Thanks for any feedback or suggestions.
Edited 9/6/2005 10:21 am ET by franklapiana
Replies
Hard to figure without more pictures/information. Bur here is a guess. I'm guessing that the whole slab was poured at one time. In the old days most were poured/mixed by hand. That is why some of its crumbling (bad mix) and the corner crack was from a cold joint (pouring the corner later than the main pour).
To repair, divide the slab into 3 section. Each section will result in less cracks. The sections would be divided on the bearing walls.
How high is this slab above the ground? Is it just a few inches because the ground subsided below it? If so you might re-pour it. If there's room enough for a crawl space or more under it, consider a framed wood structure instead of a slab.
-- J.S.
The slab was sits on the basement foundation walls - there is a full basement in each unit.
The foundations were poured first, and then the slab. Then the 2-story row houses were built on top of the slab. Unfortunately, cutting the slab or re-pouring it isn't a choice here. The first floor beams are actually set into the slab, and then the balloon framing is on top of a curb on the edges of the slab.
Two houses share the slab, and the other unit is rented out, and the owner isn't interested in major structural repairs (just bought it last year).
To my eye the entire situation is unsafe. If the slab cracks or slips, both houses would be immediately condemned. Since all of the houses in the row are connected, then all of them would be condemned.