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Let's say I have a 5" piece of rebar in a rooftop that's exposed to the elements (ie.sun, rain, salt air, etc). After some time it will be covered in rust and pieces of rust can be scraped off.

Let's say I cover this piece of rusted piece of rebar with regular concrete. Will this stop the corrosion?

  • Any rust is your enemy, especially in a perpetually wet space like concrete. I don't trust it unless it's media-blasted down to SSPC-SP10 and immediately hit with epoxy primer, followed by something to protect the epoxy from the sun. If the concrete will follow soon, you can do it all in one shot with a product like Amercote. – Harper - Reinstate Monica Sep 1 '18 at 23:30
  • I dive a wreck off the Oregon coast it was a large concrete ship, the exposed rebar is rusting away in the salt water but there are very large sections that are intact the wreck has been down in 30' of water since the late 40's I don't think you will ever see enough rust to worry about in your lifetime if cleaned and painted. Note we regularly have storms with 40' waves that move the sections around so it gets a pounding every winter. – Ed Beal Sep 4 '18 at 18:43
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No.It will continue rusting and the volume of the corrosion products will crack the concrete. New unrusted rebar will rust ( in concrete) but at a lower rate than your "prerusted" sample. Best practice is to epoxy ( or otherwise coat ) new construction. Stainless rebar is occasionally used. Bridges are a very severe service for rebar corrosion ; rebar in locations where the concrete is never wet do not have corrosion problems.

  • What would happen if I cover this rusted piece of rebar with epoxy and then cover it with concrete? – rbhat Sep 3 '18 at 13:36
  • The problem is that this rebar is in a spot where it's uncomfortable to remove it or sand it down, but I can clean it up, paint it, and then pour concrete. – rbhat Sep 3 '18 at 13:37
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    Try a "conversion" coating ( phosphroic acid + ?) then epoxy type coating, it can't hurt. – blacksmith37 Sep 4 '18 at 18:44
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The problem with rust is once it starts, it will continue. It will even steal oxygen ions from the concrete to continue rusting. Sand blast away what you can. Apply a rust inhibitor. Then apply an epoxy coating. One year from now, if there is any sign of cracks , you will know if you were successful.

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