More info, pls.

Are you setting up (excavation, forming, etc.) or is sub? How deep are footers? New sub or history?

 

I am doing all the demo (saw cuts, breaking it up, disposal)

digging, forming, rebar, compacting, eventually the new slab itself are all on the sub. Footers are 18" below grade level, 6" thick and 14" wide. The stem wall is 6" wide (2x6 + sheathing) and 6" above grade.

Have worked with this sub a lot past year, does really good slabs, driveways, stamped at good prices for me but have feeling this might be out of his comfort zone

doesn't think it would work out to form adjacent to the slab since it's too uneven, doesn't think it'll be square/straight enough working with the slab there. I don't have enough earned confidence to push back, need better opinions.

 

The 2' strip will not blend.

Your idea will work, using Tapcons to hold down 2x4 strip to hold the bottom of the form, but for it to look good, your saw cut will have to be very accurate.

As an aside, I drill a 1/4" hole like I would for a Tapcon, but then I use a short piece of tie wire and a duplex 16D. Much quicker on the install and removal both, and a lot cheaper than Tapcons.

When he says "rod over the top", is he wanting to do a monolithic slab/footing, and then build the stem wall on top? I do not advise that method, as you now have a cold joint right at or below grade level, and you will forever have water intrusion issues.

 

I like that nail idea, going to try that.

No, the stem wall and footing would be monolithic, slab poured after.

may end up self performing the footing and wall portion of this. Not too concerned about the aesthetics at the top of the stem wall since there will be stucco overhanging it by 1/2” on the outside and drywall on the inside thankfully

 

You could run a bentonite sheet along the wall to blind side waterproof that wall.

 

No water issues in phoenix valley generally but that was a cool rabbit hole to learn about. Thanks for suggesting

 

Agree with all of Seven Delta's points.

A little harder to dig the footer if the concrete is cut on the wall line, but will look much better.

Some people like to just hog everything out of the way and then patch back in, but with a little care, you can make a neat job of it.

 

Why are we trying to save the existing concrete slab?

What harm would be to have a 2’ strip of new concrete against the old?

Based on your drawing, you have to hand dig the spread footer under the existing slab?

Is the client pushing all this? Sounds like you could end up being responsible if something you didn’t propose goes south?

 

The existing is huge, probably close to 1000sqft of the backyard. Hard to delineate an end point if I werent to demo all of it.

Yeah, the underdig portion would have to be done by hand. The ahj is not persnickety fwiw.

Proposal is mine, I dont like the idea of an ugly 1-~2’ blend strip.

Talked it through with some referred subs and both were initially wanting to overcut at-least a foot but also willing to form up at the exact footprint when I suggested it. they obviously just dont want the extra hassle of getting the stem wall level when the slab around is on a slope.

At this point am leaning towards doing the footing and stem wall in house and having my repeat sub do the slab

 

Instead of a blend strip, make it a feature strip. Stamp and stain, exposed aggregate, or something else to make it purposely different.

 

Snap a chalk line on the inside of the outside form board, and set a few grade nails in the side. 👍

 

How about remove the entire existing slab? I’m not sure I see the point in going through all the work to cut the slab only so you can leave part of it there. It’s hard to come up with a solid solution without being there. But your concrete guy doesn’t sound as dumb as you make him out to be. Sounds like he doesn’t want to take any chances which is a good idea with concrete. I would meet up with him again and go over any of the concerns you still have.

 

I wish, but in this case it doesn't make sense. the slab adjacent to the shop runs under an outdoor kitchen that was built on top of the slab. there are unmarked utilities running to it (unpermitted job) no idea how deep. and on one side of the shop, not 3 ft away is a 6ft block wall that is built on top of the slab (yeah I know). I don't want to risk damaging either one. the whole slab area is close to 1K sqft but all that stuff is right next the area w/ the shop and no convenient control joints to delineate it