1

If you have seen railings anchored into concrete, you may have noticed how they tend to rust at the junction between the railing, the concrete and the air. Here is a photo of a pretty typical example:

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How can this be avoided when building a new railing?

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Honestly, I don't think you can. The problem is railings such as this rust from the inside out. The outside gets primed and painted while the inside never gets any kind of treatment.

Aside from using solid "tubing", which is unrealistic, the only other thing I can think of is to "try" to treat the inside of the tubing in areas where water can seep up in to the tubing, such as an anchor point.

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There are no magic tricks but I do have a couple of suggestions:

  1. Make sure the steel is hotdip galvanized to a coating thickness of 100µm zinc or greater. You can use paint as well but compared to a proper galvanization a regular paint is more decorative than protective.
  2. Ensure there is no electrical contact between railing and the rebars in the concrete. Otherwise the coating of the railing will act as a galvanization of both the railing and the rebars and disappear much quicker.
  3. Don't use any steel of thickness below 6mm (I prefer using 10mm when designing railings). It will not absorb enough zinc when galvanized, and any loss of thickness when it does begin to rust will result in proportionally larger loss of structural capacity.
  4. Expect to do significant repairs to the coating at least every 15 to 25 years as no coating will last longer than that in a corrosive environment. Use a paint with a high zinc content for repairs, not just regular paint.
  5. Use anchors of stainless steel — at least grade A4 — to fasten the railing into the concrete. The parts inside the concrete are protected by the high pH-value of concrete but near the surface they are very much exposed and it is impossible to apply anything more than a thin coating on threaded rods of regular steel without rendering the thread useless.
  6. Don't use any de-icing salts near the railing. De-icing salts are kryptonite for both concrete and steel.
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The metal rusts where it's in contact with the concrete because concrete nearly always has free moisture residing in it. That's also where the railing's coating tends to get chipped. Shoes, shovels, bikes, and whatever else bangs into it down low, and sidewalk salt makes it all worse.

You can be sure to have a high-quality coating on the metal parts, and you can protect them from impact damage. You can't stop the ravages of time, though. 10 to 20 years is a reasonable life expectancy for iron. Go with something else if you need more time.

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