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At my church, there is an old set of stairs made of concrete. They've begun to crumble on the top to the point where the treads are no longer flat and smooth.

I've not seen any material that has fallen off of the stairs so I can't tell you if it's flaking or crumbling off. (And I'm not sure if it makes a difference or if there is a difference.)

Is it possible to patch these concrete stairs or would the new concrete not bond well to the old? If so, can I just use some 2x10s and quickrete?

Up to this point, I've just ignored it since it would be far worse to have a giant chunk of concrete fall off (from a bad patch) than to leave it as is.

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Do you have a picture of the steps in question? –  The Evil Greebo Sep 15 '11 at 19:35
    
I wish I did. I can grab one on Sunday. ;) –  Richard Sep 15 '11 at 19:37
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4 Answers

up vote 6 down vote accepted

You can't just slap down new concrete. It will never bond. Some options:

1) They make bonding agents for this. Not sure how well they work.

2) vinyl patching compound. Probably your best bet for damages stairs. Not as good as new concrete, but might hold you over for a while.

3) Epoxy. probably the best for small repairs. I use it quite a bit for small cracks and pits.

Without seeing pictures, I'm guessing #2 is maybe what you want to try first.

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If bonding is a big issue, it sounds like it would be better to just replace the stairs entirely. Thanks! +1 for the options. –  Richard Sep 15 '11 at 19:41
    
replacement is the 'best' option in terms of quality of final product. But it's also the most laborious and expensive. ;) –  DA01 Sep 15 '11 at 19:51
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New concrete will bond to the old one, but only if the the surface is clean which is kind of problematic since concrete is porous and absorbs all possible dirt during its lifetime - it will be anything, including gum and machine oil. So concrete must must be first cleaned thoroughly for example by chipping off a layer of concrete - that is not trivial and lots of dirty work.

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I've never had to repair concrete, so I can't answer on the concrete bonding issue, however ...

Depending on how much material is missing (if it's just the corner, and maybe a little bit of the tread), you might be able to find a stair nosing that's large enough to cover the damage. You'd then instead grind down the concrete to set the nosing in, then drill & anchor it.

You can also find something called 'renovation treads', which cover more of the step, and go on top of the step, rather than being set into the concrete like a nosing. Depending on how uneven the steps are, you might be able to apply these without having to do concrete repairs.

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To bond new concrete to old concrete you need to use a concrete bonding agent. As long as the old concrete is well cleaned (pressure washed) and the bonding agent applied properly, new concrete should adhere fine.

The bigger concern, IMO, is getting a good tight seal. If there are exposed cracks between the new and old, water will penetrate and freeze and destroy your work - especially if the cracks are on the top surface where water can pool.

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Have you used concrete bonding agent before? Does it work well? Thanks for the answer. –  Richard Sep 15 '11 at 19:42
    
Once. (I haven't done a lot of concrete work, I just watch a LOT of Mike Holmes and remember what he says about it). Before: lh3.googleusercontent.com/-PfYT9SYYctI/TlRBI1bzL0I/AAAAAAAAAx0/… After: lh3.googleusercontent.com/-T6TWYITy_Do/TlWSmkaDs_I/AAAAAAAAAzo/… -- so far so good, but it's new work... so YMMV –  The Evil Greebo Sep 15 '11 at 19:44
    
Nice! Many thanks. –  Richard Sep 15 '11 at 19:48
    
I've used it before. The key was to get the old surface clean, apply the bonding agent, AND add some of the bonding agent to the concrete itself. If you live in a climate that has a freeze-/thaw cycle, I'd be sure to use a material that can be spread thinly and I'd coat the whole staircase so that you have a lower risk of water intrusion. –  Karl Katzke Sep 20 '11 at 17:56
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