Concrete on top of concrete?

[nielloeb]

A tree root lifted part of the sidewalk leading to my door three inches. I cut the root so it won=92t grow and am going to pour a concrete ramp on top of the existing sidewalk so no one trips anymore.

Is there anything wrong with the following?

Use Concrete Mix to go from three inches to two inches. Use Sand/ Topping Mix to go from two inches to 3/8 inch.

Make it 36 inches long =96 approximately one inch drop per foot -- which means 15 inches long to go down to two inches and 21 more inches to go down to 3/8 inch.

Build forms on either side of the existing sidewalk, going from three inches to 3/8 inch, with a piece going across to stop it at two inches.

Clean and wet the existing sidewalk.

It=92s not necessary to paint on Concrete Bonding Adhesive to the existing sidewalk, as this is just a little job for a sidewalk that gets little traffic.

Mix the concrete mix a little thick because it has to maintain the angle of the ramp. Pour it into the form. Use a screed =96 i.e. a 2x4 to level it and push it down, getting rid of air bubbles. Use a trowel to make sure it=92s level and there are no low places to gather water.

Let it dry long enough so you can safely remove the cross piece at the two inch mark without the new concrete falling.

Mix the Sand/Topping Mix a little thick because it has to maintain the angle of the ramp. Pour it into the form from the new concrete at two inches to the end at 3/8 inch. Use a screed =96 i.e. a 2x4 to level it and push it down, getting rid of air bubbles. Use a trowel to make sure it=92s level and there are no low places to gather water.

It=92s not necessary to paint on Acrylic Concrete Cure and Sealer to the new concrete, as this is just a little job for a sidewalk that gets little traffic.

It=92s not necessary to wet down the whole thing a few times a day for a couple of days because the temperature will be 50 to 78 degrees and the sidewalk is in the shade.

[Nestor Kelebay]

[e-mail]:

I would use a concrete bonding agent wherever you want new concrete to stick to old concrete.

I would staple 6 mil vapour barrier over the new concrete as it cures to prevent moisture evaporation from the surface of the concrete so that it cures harder. That will replace the acrylic curing agent and the wetting down every few hours for several days.

------------------------------------- ..in solidarity with the movement for change in Iran.

[aemeijers]

Random ramps are still a trip hazard, and a 3/8"-edge overlap will flake off, especially if you live in ice and snow country. Tear out the lifted square, cut the root out, put down well-tamped gravel and pour a new square. It really won't be much more work than what you are proposing, and the odds of a good result are much higher. If you ever plan to sell, a walkway repaired like you propose would be a red flag to inspectors, and a turnoff to most buyers.

[RicodJour]

Unless the prospective buyers are tweens and into skateboarding. ;)

To the OP: Any other type of repair is an exercise in futility, and a waste of time, effort and money. If you know that you're cutting corners and looking for validation, try alt.repairs.hacks.

R

[hrhofmann]

I would lift the old slab, cut the root oiut, and then reepair the base and place the slab back down. If youleave the root, iot will rot and eventually sink back down. If you can wait for 4-5 years for the root to rot, then things will be level again, it's much easier to remove the root, relevel the base and put the slab back down or maybe our a whole new slab.

[Steve B]

I am with you on this. I have had only ONE concrete repair that stood up. I had a bottom landing on my cabin that was coming off due to freeze/thaw cycles, and water on top. The concrete was going away, eating its way downward, and leaving exposed aggregate. I went and got a 40% box of PourStone, and mixed some up. Troweled it on top. Just wanted it to last one year until proper steps were made, and that old wrecked out. Plans and economy changed, and the step is still there three winters later. PourStone looks new. Every other time I have feathered out concrete, it started cracking off at about the 2" thickness line, and waaaaaaaaaaaaay before

3/8". You could feel it cracking under your feet on the really thin stuff. Get a quickie saw, cut the bad out, and do it right the first time. If you do it on the taper as you propose, water gets in there and freezes and thaws, it starts cracking on you, you are only going have to do it again.

Do it once, do it right.

Steve

Heart surgery pending? Read up and prepare. Learn how to care for a friend.

[nielloeb]

Thanks for the replies. Keem them coming. It's nice to have a USENET group that is not only a community, but that hasn't been taken over by spam. I forgot a step: brush with something like a broom to give it the same rough texture as the rest of the sidewalk and more grip. The Sand/Topping Mix is specifically made to go down to 3/8 inch without chipping; especially so, in that I don't live in a freeze/thaw zone. And 3/8 inch is acceptable under the Americans with Disabilities Act.

[RicodJour]

You received five negatives and one positive, so of course you ignore the negatives. Good on you!

R

[Jim Elbrecht]

And just in case the 6th 'No!' is the charm, I'll repeat what the others have said. Don't waste your time trying to patch. Remove the root & re-pour that section.

I'll bet all of the folks who are saying 'don't patch' have either BTDT, or had to re-do someone else's 'easy way out'.

Why ask here if you're going to ignore all the experience represented here?

Jim

[RicodJour]

Allow me to modify your acronym, Jim. BTDTHTRIOADIARTT Been there done that had to do rip it out and do it again right this time.

It's threads like this that make me wish that an OP would post back later. I really love saying I told you so.

R

[Una]

They're saying don't do this because so thin a slice of cement is going to cure weak and thus will be likely to crumble.

I too would lift off the square, cut out the already severed root, and reset the square.

Una

[Steve B]

How big a square we talking about here? That stuff is pretty heavy, even the small ones. Unless you have a bunch of strong sons, a lift, or something to do it with, doing it that way is not going to be easy. And then, how are you going to get the square to lay level without settling, and giving you a trip hazard? One way might be to dig out, pour some fresh cement in, and lay the square on top, and tamp down, but it would have to be figured perfectly for it to come out flush, and like I said, it would take some manpower or mechanical means. By that time, one could mix up some concrete and be done. I can do four 80# sacks of premix in my machine at one time, and take less than ten minutes to reload and pour another four sacks.

Steve

Heart surgery pending? Read up and prepare. Learn how to care for a friend.

[Una]

Pouring a replacement slab involves first removing the perfectly good original slab, which is just about as much work as moving it out and back in again. Then you still have to buy the cement mix ingredients and mix them in something, and pour, and clean up afterward, and wait while the slab cures...

Resetting a sidewalk slab of concrete is just like setting a flagstone. It is no big deal.

Tools: long prybar, and some rollers. For rollers use an old steel pipe or a young straight tree trunk or old pole cut to short lengths. Pry up the slab, slip rollers under, pry the other end of the slab to roll it along on top of the rollers. In this manner I moved all by myself a slab 3'x3' by 4-6" without breaking a sweat or making a mess. Your slab should have been set in a bed of coarse sand; if it was set in dirt, remove a few inches of dirt and replace with sand.

If this sounds the least bit daunting, hire a handyman to do it all. It's a minor job, about 1 hour, 2 if the bed needs to be replaced.

Una

[Edward Reid]

I'll second that. It may not look like much, but when you're not looking for it, it's a problem.

I used to travel to Los Angeles frequently. In the Delta terminal at LAX, about half way back, there's a long ramp, maybe 100' long, that drops down to go under something (I don't know what) and back up. The slope is about what you're talking about here, even less.

Of course the ramp itself isn't a problem. But about half way down, on both sides. there's a section about 3' long that's level instead of following the slope. The appearance doesn't change -- the floor is laid so that it all blends. And every time I walked down one of those ramps, I would stumble when I reached that level spot, even though the change in slope was tiny.

So if you insist on the repair as you laid it out, at least add a colorant to the concrete so that it's a radically different color. It IS a bump that people can trip on, so make it obvious.

Edward

[jw]

Here's another tip. When I break out old concrete, I use the broken stuff as part of the new. Get the chunks down to about 8 inches or less. Lay them in the hole where the new concrete will go, leaving at least 2 inches between the pieces. Put them deep enough so the new stuff is at least an inch thick on top. Wet them before pouring. They will become part of the slab. I do the same with rocks. It always holds up well, and was a trick used by farmers for many years since rocks are/were always abundant on farms. You save lots of money this way and get a good slab. But there's more. If you use pre-mixed bagged concrete, add a little more portland cement to make a harder mix. After wetting the rocks/old concrete, sprinkle a little raw portland on them before pouring. Make it adhere better. One of those hand operated lawn seeders will spread the powder, or just hand sprinkle it. (wash hands after, portland is hard on the skin).

[Steve B]

mmmmmmmmmm

To me, when you have all that exposed and dug up, I don't see where one can "save a lot of money" by using old concrete debris. Yes, it will fill a certain volume, and that is less bags of concrete that one would not need. But the surface adhesion of the new concrete to the old blocks would be questionable, and later on ............. maybe cracking of some type of failure.

When I spend that much time and work to dig something up, I don't like to skimp on the fix, and risk the chance of doing it all over again.

YM(and probably does)V

Steve

Heart surgery pending? Read up and prepare. Learn how to care for a friend.

[jw]

Like I said, it's always worked fine for me, and farmers have done it for many years. (I am a farmer). I have never had a failure, in fact it seems to crack less than new concrete. And, actually it saves very much concrete, like 50% or so. The object is to dump the chunks in the hole and level them so they are not too high. Wetten them and the gravel underneath. I tend to walk and jump on the larger pieces to embed them against the gravel. Works every time.

[RicodJour]

I bust up concrete all of the time and reuse it as large scale aggregate and I've never had a problem. The post you were responding to was a bit misleading, though. To bust up sidewalk concrete into 8" pieces and reuse it in a new sidewalk pour would seem to create a concrete mosaic surface. Maybe that's not what he meant, but that's how I'm reading it. He might mean to excavate down some more, and bury the busted up concrete that way, but they you're dealing with more excavation and have to relocate the dirt.

I bust up the concrete so it's in smaller pieces for a slab, no bigger than half of the depth of the new concrete, place it in the bottom of the form and pour the concrete on top. I do it more for "reuse, recycle" reasons than anything else - I have to dispose of less and it's not a compromise. But you're not getting rid of a section of slab by reusing it in the same size replacement, maybe a third, and for one small section it might not be worth the effort for some people.

R

[Steve B]

Like I said, YMM(and probably does)V.

[Existential Angst]

Allow me to modify your acronym, Jim. BTDTHTRIOADIARTT Been there done that had to do rip it out and do it again right this time.

It's threads like this that make me wish that an OP would post back later. I really love saying I told you so. ==================================================

Indeed. You make it repeatedly clear that you are a spiteful judgmental semi-litirit dickwaving pre-maturely aging wretch.