Pour thin slab over existing sidewalk?

[HerHusband]

I have a 3'x8' concrete sidewalk connecting our house and garage. It is 4+ inches thick, reinforced with rebar, and it's in great shape. However, I need to raise the walkway up to improve drainage slopes.

If I poured a 2" slab on top of the existing sidewalk, would it hold up without cracking?

It would be the same size as the existing slab, so I'm not worried about different settling at the joints or anything. I'm also planning to pour new slabs on either side so it won't be able to shift side to side. I wouldn't worry if the new slab was thicker, but I've never poured a slab that thin before.

Thanks,

Anthony Watson

[Pico Rico]

I don't know, but what is the existing slope and what is your desired slope?

[gfretwell]

2" is thick enough to be pretty stable. I would acid wash the existing slab and paint it with a bonding agent to help the bond and transfer any expansion joints you have to the lift. You could dump the left over bonding agent into the new concrete to make it tougher.

[rbowman]

From my experience, no, but then the area commonly had sub-zero (F) temperatures in the winter. That was years ago and the bonding agents may have improved though.

[micky]

Will you be pouring the adjacent slabs at the same time you pour these 2 inches?

[HerHusband]

The existing slope is fine (I don't recall the exact pitch at the moment), but it was installed years ago before we had our driveway drain. Now the low end of the walk is too low to slope into the drain properly.

We have a paver patio on both sides of the walkway that has settled unevenly over the years. I'm wanting to replace the pavers with a concrete slab and reuse the pavers in the back yard.

Since I'm redoing the patio anyway, it is a perfect time to get all the slopes right so everything drains nicely.

Thanks,

Anthony Watson

[HerHusband]

That's what I figured, I was just hoping for the lazy solution. :)

My 3'x8' slab isn't that big, but it's 4"-6" thick and reinforced with rebar. Unfortunately, I built it to last forever so it will take a bit more work to tear out.

Better to do it right and not take shortcuts. I will tear out the existing slab and pour a new one. I can always use the debris as fill in other areas I need to build up.

Thanks for the feedback!

Anthony Watson

[Ashton Crusher]

What about this... Pour the new stuff on each side but block off the area over the old. Then put in thin brick pavers, if they make em thin enough, on sand bed. Drill some drainage holes in the old slab so the pavers can drain out excess rain water.

[HerHusband]

No, I like to pour every other slab first, then come back and pour the remaining slabs later. It's just easier for me to handle that way in the confined area between the house and garage.

That's the method I used on the opposite side of the garage and it worked great.

The pro's would probably do it all in one pour. I'm not a pro. :)

Thanks,

Anthony Watson

[micky]

I ask because if even one square on each side were poured at the same time, it would hold the 2" addition in more tightly.

One might even be able to run rebar though the 2" part to the 6" part.

Not that I've done this. My only experience with rebar was putting it down for an interstate highway, and I haven't been back to see how well everything lasted.

[Mayayana]

| >> If I poured a 2" slab on top of the existing sidewalk, would it hold | >> up without cracking? | | > From my experience, no, but then the area commonly had sub-zero (F) | > temperatures in the winter. That was years ago and the bonding agents | > may have improved though. | | That's what I figured, I was just hoping for the lazy solution. :) | Caveat: I don't have extensive experience with concrete. But I've used on-top patching with sandmix and bonding liquid. I also live in a cold region. If the sidewalk is stable I wouldn't expect a problem. But I wouldn't use concrete mix that thin.

[philoÂÂ]

Hire someone to mudjack it up

[Art Todesco]

I had 2 rectangles of sidewalk, in my previous house, that were tipped because the original builder didn't allow the under fill enough time to compact. As it got worse through many years, I hired a company that used a concrete pump to push cement into holes drilled in the slab. I guess this is mudjacking? The results were unbelievable ... only remnants afterwards were a few 2" holes nicely patched with cement.

[philoÂÂ]

Due to tree roots, I almost lost my entire porch. After the tree was removed and as much of the roots as possible, I was facing a total porch rebuild due to a badly tilted (old style) cement block pillar.

I hired a "mud jack" outfit that pumped in cement underground and got it dead even. That was a few years ago and it's stayed perfectly in place.

[trader_4]

If it were me, I'd just go with the 2" on top. As long as the concrete that is there is stable, I think

2" thick on top would be OK. And it's sure a PIA to break up 4" thick concrete with rebar. And then what do you do with it?

[HerHusband]

I am still debating whether to take the easy approach. :)

The 3'x8' slab that is there is very solid. It rests on the footings of the house and garage and is reinforced with two half inch rebars. It's not moving anywhere, so it would make a very solid base. It would certainly be a better base than compacted dirt or gravel.

My only concern is whether 2" thick concrete would hold up.

When we built the garage back in 2001, I poured a small 2'x3' step in front of the garage entry door. After we built the house in 2003/2004, I had to break up the old step so I could pour the current 3'x8' walk between the two buildings. You're right, it was real pain to break up that step, and it was a lot smaller than the current walk. Still, it's doable if I decide to go that route.

I have plenty of places I could bury the old concrete chunks if I tear it out. So at least that's not an issue.

Thanks,

Anthony Watson

[TimR]

Concrete gets stronger for the first 50 years, other things being equal. I've seen some old concrete that was not so easy to break up.

[micky]

They mentioned that at the Panama Canal. They said if a ship hit the lock walls, it was the ship that broke.

[Arthur Conan Doyle]

Without special measures, Boulder Dam would have taken 125 years just to get to ambient temperature. Actual curing never stops, although it slows down considerably.

[clare]

Back in 1965-66 I had the job of breaking out concrete stabling in the barn. The sledge hammer weighed about as much as I did at the beginning of the summer. The box stalls were the worst, but breaking out the stable floors to put in the stable cleaner was not easy either. The concrete was over 50 years old and had been mixed pretty strong when it was put in.