How quickly will rebar rust through?

Hey all,

I'm building a backyard brick oven based on plans from the book "The Bread Builders." Overall the plans seem reasonable, but one detail has me scratching my head. After pouring a concrete slab and building a block foundation, it calls for a 3.5" thick hearth slab with rebar extending outward 4" on each side (spaced 1' on center). The extended rebar sits on top of the top row of blocks (with cores filled in).

I'm wondering how long it will take for the rebar to rust through to the point where it is no longer strong enough to support the weight of the oven cantilevered out onto the block wall. The rebar will be protected from the elements by a brick enclosure, but I'm still left wondering how many years it will be before I find the oven has crashed down to the bottom slab.

Anyone have thoughts? I can provide more detail on the design if needed.

Jeff

 

I have seen it exposed in never finished coastal (as in on the beach) structures that were at least 20 years old then, and the remains of iron vessels actually in the tide that were 50 years old.

 

Thanks. I think I'm going to go with the design as written. This will give me the flexibility to move the oven if I ever need to.

 

You can also pose your question here:

Forno Bravo Forum: The Wood-Fired Oven Community - The Pizza Oven Installation and Cooking Community

Lots of brick oven projects during the building process are put on hold during winter months or for other reasons.

I am planning to build a pompeii pizza oven next to my current concrete patio project I'm working on...

 

Iron will only rust until the rust stops the infiltration of oxygen, then it will stop. When they built the Omni (Atlanta basketball complex) they did not finish the exterior steel, but let it rust. After a year or so, it had a great patina to it, and it rusted no further because the air was blocked from the iron.

 

That is a special type of iron. Iron oxide, unlike other types of oxidation like aluminum oxide, does not prevent continued rusting in mild steel. It does slow it down a lot, though.

 

I agree, but I don't think rebar is mild steel, would you think? Could be, just a thought.

 

Common rebar, grade 40 and 60 are mild steel.

 

Rebar will rust through. The time required is very dependent on the environment (temperature, humidity, pollutants, salt, etc.).

The best way to avoid the problem is to coat the ends that will be exposed with zinc. You can do your own hot dip with a piece of pipe (capped at one end), a torch and some zinc. Hit the rebar with a wire brush before dipping it.

Second best is to keep the exposed ends painted.

Hope this is of some use.

Cheers,
Don

 

Thanks to all who have replied. So far construction is going well. I'll be sure to put some paint on the rebar ends before I wrap the oven in the enclosure. And photos will come along sometime in the future, too.

 

I worked 8 years of heavy construction and I can tell you that when I did government work for the state where we made road barriers, that all the rebar had to be painted before it was put in the cement.

Cement has a tendency to cause the metal to corrode -anywhere - where it is exposed. As long as it is not exposed, it will last a very long time. There is cement below my house that was poured back around 1890 that was piers for the tipple for a coal company that closed in 1941 and the cement still looks as good as the day they poured it.

Then again there is bridges we built back in the 80's that had calcium chloride and salt put on them and they fell apart.

Anytime the rebar stuck out past the cement - we had to coat it - because the rust would travel back inside of the cement if left untreated.

I would suspect that if you used 3/4 inch rebar that it would last 40 years at the most in a oven.

We had a fireplace up at our camp and went through several sets of grates. One set my uncle bought was made out of 3/4 octagonal steel and the embers from the logs melted the steel.

If I was to make a fireplace or a wood stove to bake bread, it would be lined with firebrick and not rely on rebar to hold anything up.

This bakery is a very old and very famous bakery in Dubois Pa that started out called Zappia's bread. My Uncles nephew bought the place a few years ago and reopened it. It still has the original homemade oven.

Calliari's Bakery - Home Page

 

http://www.zwire.com/site/index.cfm?...d=572984&rfi=8

I believe that the oven is either coal fired or wood fired.

 

Painting exposed rebar is OK (but a product like Ospho is better), but embedded rebar should NOT be painted.