The Wire Mesh story revisited

I previously told the story of how Ronnie dropped off nice clean shiny looking wire mesh on Monday July 11, but then started to install very rusty looking wire mesh just before the concrete pour on Wednesday July 13, but I immediately called and convinced him to use the cleaner mesh (for which I had already prepaid $330 including installation, two weeks beforehand) by agreeing to pay yet another $100, which he later told me not to worry about when I ultimately wrote him a check for $100 for the upgrade of concrete to 4000 PSI (which should only have costed <$20).  The whole affair looked like bait-and-switch, extortion, etc.

Now it turns out that rusty wire mesh is actually pretty commonly used in concrete work, and might have actually been the "correct" kind of mesh, whereas the shiny mesh was actually galvanized fencing material which could be claimed to be an incorrect choice, or perhaps a better choice, depending on who you talk to.

Of course, if the galvanized fencing were an incorrect material, Ronnie should have never dropped it off in the first place, and simply explained the fact that it was incorrect, whereas the rusty stuff was the correct material.  He did say that the rusty stuff was "exactly what you get at Home Depot" (but see below), but he never said the shiny stuff was wrong.

Anyway, I did indeed see very rusty looking wire mesh sold for concrete reinforcement not at Home Depot but at Lowes on Austin Hwy:

Meanwhile, at the Home Depot near Evers Pkwy, I saw much less rusty looking mesh sold for the same purpose, but it was dark colored.

The shiny material is actually galvanized wire mesh, commonly used in fencing.

 So now I actually might wonder whether putting the shiny stuff in the concrete was a bad thing.  However, my best research suggests that it was probably not a bad thing for several reasons, and probably a good thing overall.

First it has to be remembered that the wire mesh was merely a supplement to already over-engineered rebar system.  The rebar system keeps the slab structurally sound, while the mesh simply serves to minimize superficial cracking.  So even if the galvanized mesh is not as strong as the uncoated stuff, it doesn't matter much.  The galvanized mesh is also "welded wire mesh", just like the rusty stuff.  I don't know if the gauge of the galvanized material was larger or smaller, it looked about the same, but even if it were slightly smaller gauge, it wouldn't matter much.  Sometimes in small patio slabs or walkways people even use galvanized chicken wire as the main reinforcement!

Now as suggested by the casual use of galvanized chicken wire in some cases, the galvanized coating is not known to be harmful to concrete.  But sometimes the claim is made that a chemical reaction between the coating and the cement over time releases hydrogen, which can embrittle the steel.  So, over time, the steel in the mesh might become less strong.  Once again, this is not a huge issue because in my application the mesh is not providing the primary reinforcement, only a secondary reinforcement to minimize visible cracking.

But this very embrittlement hypothesis is greatly disputed by the Galvanized Metal Industry.  They say the released hydrogen dissipates through the concrete and doesn't affect the metal at all.  In fact, they claim that galvanized metal would generally be better than "black steel"  for all concrete reinforcement purposes because of its anticorrosive properties, and is especially useful in preventing corrosion in chloride rich environments.

http://www.galvanizeit.org/aga/about-hot-dip-galvanizing/how-long-does-hdg-last/in-concrete

It appears that corrosion of rebar is a major factor in the deterioration of reinforced concrete structures over time.



This is especially an issue for chloride rich environments, such as near the ocean.  In most environments, the calcium hydroxide of cement itself (having pH of 12.5) pretty well inhibits concrete corrosion, though that can effect can be negated by intrusion of salts or other chemicals.

So by insisting on the cleaner looking galvanized mesh, it looks like I made a good choice, even if it is not the industry standard.  It is superior to the industry standard.