July 11, 2019 at 5:04 pm #726707
so, the raised concrete slab got poured wrong (no footer) so the dirt/gravel base underneath is loose and exposed once the forms came off. I know this was done wrong, but now my question is what to do, considering erosion is going to slowly compromise the base.
Should I work as much as possible to frame a pressure treated wood wall around the bottom?
If I build mounds around it will that help (I doubt it as I would assume the material under the slab would slowly dribble out as erosion on the mound happened….
Thoughts? Any other ideas to help fix my mistake?
here are some pics
Attachments:July 11, 2019 at 5:26 pm #726710DoobieModerator
I’m by no means the concrete expert here, but here’s an idea – aside from breaking it up and starting new.
You know how they have those guys that can raise a sunken slab by drilling some holes in the slab top and pressure filling and rising the slab up? Well maybe you don’t, but still, using something along those lines, excavate the perimeter crap that would be ready to creep out in due time as you rightly predict, frame the base all around, then get that injection type concrete to shore up the edge all around just as it should have been done in the first place.
Of course afterwards, the boarding is removed once it sets. You’re idea of just shoring up with boarding won’t last. PT in dirt contact buried, even ground contact rated PT, won’t last. It’ll rot and just be an arduous recurring job every few years to deal with.
There may be a DIY way of doing this, but I think you’d need a pro in that type of concrete remedial work.
Aside from that, is there any way to build up the surrounding area to mitigate the future errosion? I suspect it’s not feasible hence your query. Diģging further down all around the outer perimeter and putting in a good 10 to 12 inch sub-base of either A gravel or my newly preferred choice of steel slag and laying paver stones all around the affected areas might also solve this. MIGHT. Hard to really rubber stamp that idea seeing two pics on the internet and not up close and seeing the full picture of everything surrounding. Good luck…no idea if that’s really feasible. but it’s an idea to help create a perimeter crown edge which is what should have been created in the first place.
Did you do this job yourself – no shame is saying so, concrete is way more complicated than most people even seasoned tradesmen but occasioanl concrete dabblers realize. All those YT videos and how-to books try to make concrete work look easy. It’s just not that easy to do it right.July 11, 2019 at 7:20 pm #726719
I do like your idea, it’s more expensive, the the DIY is what got me into this mess in the first place. THANKS!July 11, 2019 at 8:23 pm #firstname.lastname@example.orgProOwatonna, MN - Minnesota
If the slab has not moved yet, I would just pack soil around the slab to within 4″ of the top to keep the sub-base below the slab in place. Absence of the thickened edge to retain the base below the slab, something has to be done to keep the granular fill below the slab in place.
I have seen similar situation on a driveway when a rain comes before fill is placed against the edge of the slab and the sand below washes out. Packing soil against the slab will take care of the problem and we have never had issues with that.July 11, 2019 at 8:42 pm #726726
Kurt, thanks for that idea. I had a few “buddies” suggest that, but my buddies and I got us into this mess 🙂
I’m thinking QUIKRETE-Hydraulic-Water-Stop-50-lb-Cement to fill in the current voids and then to make a makeshift face (downturn) and then landscaping the heck out of it to shed water away to keep it from washout.July 12, 2019 at 7:32 am #email@example.comProOwatonna, MN - Minnesota
I think the water-stop may be overkill as it expands as it dries unlike normal mortar that shrinks as it dries. I would just use a non shrink grout, not an expanding grout to fix up the edges and then landscape.
At this time making the downturn unless it extends at least 6″ to 8″ back from the edge of the slab is almost a waste of time. Anything thin and unreinforced, will just break away.
You could dig around the slab and do a modified underpin if you are really worried, but I would say landscaping is the best option at this time. A 1 or 2 foot tall retaining wall a couple feet away from the slab, may do wonders to fix your situationJuly 12, 2019 at 8:45 pm #726798Seven-Delta-FortyOneProThe Emerald Triangle, Northern California
What is this slab for?
I can’t tell from the pictures.
My advice will be different based on if it’s a patio, or a slab-on-grade foundation.
Goin' Down In Flames........September 3, 2019 at 10:19 am #730918MiamicuseProFort Lauderdale, Florida
There is no footer around the base at all?
How was the soil base compacted?
What kind of dead and live loads will be on the slab + roof? A car lift?September 3, 2019 at 12:20 pm #730920Seven-Delta-FortyOneProThe Emerald Triangle, Northern California
Don’t know if he’ll be back.
He got some good advice on some other forums he posted this at as well.
If I remember correctly, it’s a slab for a pole barn 😮 with out footings. 😮
We advised him to saw cut the perimeter, and pour a footing…
Pour a footing outside the slab, and make the building bigger.
Goin' Down In Flames........September 3, 2019 at 8:07 pm #730938smallerstickProNorth Bay, ON
I’m by no means the concrete expert here,
BE the change you want to see.
Even if you can’t Be The Pro… Be The Poster you’d want to read.September 4, 2019 at 4:17 am #730962LesliePerryPro
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