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Flaking concrete surface? Answered

Thanks for this class! I am a potter but have often thought I would like to try concrete for larger projects.
I have a question about a retaining wall and steps I had built last year. The surface of the steps flaked off badly after a long snowy winter, exposing the aggregate. Now a corner of the retaining wall has chipped off. Besides the cosmetic issues, I am concerned about the interior strength of the retaining wall. It does have rebar in it.
Also can the surface of the steps be repaired or would a "patch" just flake off?
I have been told that the concrete wasn't sealed and that the surface wasn't worked enough so that the aggregate wasn't pushed down far enough.

3 Replies

mikeasaurusBest Answer (author)2017-07-04

From what you describe it sounds like the during curing the surface didn't have enough moisture and weakened. The result can be flaking/chipping. This is especially bad news as exposing the reinforcement can lead to corrosion and structural failure (I'm not an engineer and can't comment on the seriousness of your specific case).

You can add a patch over the concrete, but in my experience patches don't always bond to the base and can lead to problems later down the line. Depending on your case, you may want to have a professional take a peek and see what their expert eyeball reveals.

If it's not a critical or important structural element, you could get away with a simple patch job and examine again in a few years to determine if more drastic measures are needed. The important part is to protect the reinforcement tp prevent corrosion.

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MarkS717 (author)mikeasaurus2017-10-15

The flaking may have been caused by salt if you used some for de-icing. Same thing happened to me and luckily over several winters has not got any worse - no more salt. Re repairs, go to the technical department of a major company who makes tile cement, specialist cements etc. Over here its Saint Gobain amongst others. They will point you in the direction of a good repair product. Just work in ideal conditions i.e. not hot or freezing and THOROUGHLY clean the steps before and soak them over a long period so they are damp (not wet) and you get a slow set. Cover if you can with a thin sheet of plastic -like you use for decorating dust sheets. Good luck

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Another suggestion for why it is flaking ...you may have had a bad mix of gravel that had some clay in the mix. This will also cause flaking.

I have also added plain white carpenter's glue to the mix, and painted the surface to be repaired with the glue also. For the wall area you could also add lime which makes the concrete into more of a "Mortar Mix" This then trowels on creating a smooth surface.

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