Rusting in the fermentation room. Explanations?

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Hello all,

Recently I have come across a problem that I cannot seem to understand. A fermentation room was built out of an insulated wall system provided by a company called BONDOR, started to rust at the corners of the joints between the walls and ceiling. The rivets started rusting as well but to my knowledge, it cannot be the rivets because they are aluminium... Also the screws and sliding door track bolts/washers supplied also started to rust. I phoned the company and was asking if their panels were able to sustain the heat and be used as a fermentation room. Of course they said yes, as I asked before I purchased them of course, but just to be sure, I asked and got it confirmed.

They claim that many others use their products to build such rooms with the same material. (Specifications can be found at [Broken] )

Anyway, they asked me what chemicals were present in the room and during the fermentation process. I told them exactly what was used. The room was used to make bread. Apart from that, additional steam was produced from a machine within the room. Now my question is, what is causing the rusting?

The composition of the bread is listed here:
Per 100KG of Flour, there'd be
1% Improver
1% Yeast
0.5% Gluton
0.5% Soya
1% Sugar
1% Salt
0.5% Milk Powder

With my basic understanding of chemistry, I can say fairly positively that those substances that make the bread do not corrode with the metal sheets of the wall panel system. And I'm sure the company was not lying to us as it is a huge company. So what is causing the corrosion?

Summary and Additional Info:
The rust eats at the corners between the wall and ceiling, behind an aluminium angle fixed with rivets. The room was hardly cleaned by the workers. Only the ceiling panel was corroded, side panels barely corroded with some patches appearing every now and then. Also at the centre of the ceiling panel, there is a sprinkler system that belongs to the plaza, something we cannot afford to touch. Rivets and bolts/screws provided, all rusted and the room would be left there after the bread was ready to be baked (and then used again to ferment the next batch of bread - this went well into around 20months) Additional substances may be present but the person who makes the bread says that's what makes the bread and no other chemicals were used. Can someone come up with logical statements of how the room started corroding?

(The old fermentation rooms were also not cleaned and they were used for around 10 years before corroding, why would this one corrode so fast ie. not even 2 years?)


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jim mcnamara

It depends on what metals are exposed behind the scenes and/or what metal coatings are in the areas that are having problems.

Anyway, one possibility is:
Fermentation produces carbon dioxide as a byproduct (the gas bubbles that make bread rise, for example). Carbon dioxide will react with water or water vapor to form carbonic acid, which will corrode some metal coatings. And will also increase oxidation (rusting) rates of some exposed alloys.

Galvanized sheet metal is coated with zinc.

For example, zinc coatings can react with carbonic acid to form zinc carbonate, which effectively removes the protective zinc coating, allowing steel underneath to oxidize. Oxidize means rust.

Plus, living in acidic conditions speeds up rusting of a lot of iron alloys.

If the problem areas are stainless steel, then the rust you are seeing is from cheaper secondary metals components that are part of the underlying frame. Stainless is resistant to rust.

Those are my guesses.
But what made the older fermentation rooms rust at say 10years rather than the newly built ones, which has started rusted not even 2 years upon construction? The baker, says nothing has changed. So I don't know why that older ones rusted at a later stage. If what you're suggesting is happening then wouldn't the same thing occur to the older ones?

By the way, thanks for the response, as I'm being pressured by 2 sides of the situation to get this problem sorted out. Perhaps what you've provided may help.


Staff Emeritus
Science Advisor
Reading the BONDOR brochure, I see a comment on page 6 in the table entitled "Properties", which mentions "(0.6 mm steel facing sheets)". Rust implies some galvanic corrosion of iron (Fe) in steel. Any moisture serves as an electrolyte, and if there is dissovled gases, particularly oxygen in the moisture (condensation) then rust is possible. Galvanic corrosion also requires the presence of an anode and cathode. Aluminum and iron (Fe), or Zn and Fe, will for a galvanic couple under the right conditions.

Now the question is - what kind of steel are those panels? Are they a structural steel, maybe a plain carbon steel, i.e. not stainless steel, or are they stainless steel, e.g. 304SS or 316SS? What other metals contact the steel?

Is chlorine bleach used to disinfect the area? Chlorine bleaches will undermine some stainless steels.

It is also possible to have what is known as filiform corrosion, which is a special type of crevice corrosion. If you have something that looks like filaments of rust, then its probably filiform corrosion.

Differences in metals (steel composition and impurities, e.g. sulfur, phosphorus, . . .), atmosphere, coating type, galvanic couplings could contribute to differences in corrosion.
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I think the sheets are galvanised steel and no, not stainless steal.

I'm really not sure what is used to disinfect the area, but hell... I don't think they really even clean it. It's pretty dirty. Would that also contribute to rusting?

I don't think there are other metals making contact with the panels itself. Apart from the angles used to cover the corners of the structure. It is powder coated aluminium angles which are riveted using aluminium mill rivets.

I'm sort of really leaning on the fact of atmospheric differences which are causing the corrosion. I'm still unsure... The suggested reasons are all very valid to this point.

Mister X (As I shall call him from now on - owner of the store) was happy with a really simple explanation and I guess he's kind of accepted this situation as an unlucky encounter rather than from dodgy material and craftsmanship.

As a final note, I really think this place is great. Apart from being a little slow on responses, I get a pretty technical and nice reply. I love you guys.


Forgot to thank you both.
Thank you, Astronuc and jim mcnamara.

I forgot to ask, are there any suggestions as to get rid/stop the rust? Maybe take down the existing 3cmx3cm aluminium angles and perhaps scrape off the residue, spray it, silicon seal the back of the aluminium angle that covers the rust and rivet it back on. We could drill out all the old rivets and replace them with powdered coated aluminium rivets.





Staff Emeritus
Science Advisor
What are the temperature and humidity like in and outside the room.

I suspect this is a matter of condensation perhaps, and the air which condenses probably has a lot of dissovled oxygen, and maybe CO2, which might affect pH.

Dirt could be a factor, and so could any microbes. Dirt can set up a 'crevice' effect, so crevice corrsion could be a factor. Microbes can cause microbial influence corrosion (MIC).

Dirt or crevices can contribute to concentration gradients in the electrolyte which can establish variations in soluble oxygen which drives the corrosion mechanism.

The recommendation on filiform corrosion is to reduce humidity, i.e. dry air. But is that practical in a fermentation room? Otherwise find a way to seal the surface of the steel panels.

BTW, to what are the Al channels fastened? Presumably another metal?

With regard to galvanized or coated steel, if the surface is scratched to the steel, then there could be a corrosion problem around the scratch. Also, the surface might be coated, but the ends of the steel sheet may not be coated or the coating maybe less effective (unless the steel was dipped after cutting to size).

Levi, When you mention "perhaps scrape off the residue", are you referring to the rust? If so, that might simply expose more surface. Certainly clean away the rust, and in past, I have used something called 'Naval jelly' with phosphoric acid, which dissolved the rust and cleaned the surface in preparation for applying a rust inhibiting coating. 7 Tech Sheets/naval_jelly.htm [Broken]
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I was informed that the operation termperatures are around 50C and I've only seen what the oven looks like after the fermenting of the bread. It's practically just all steam and after it cools down, the steam become water droplets that fall back onto the floor or escape through small holes that may be present in the room (?)

And like I said before, it was really dirty so I've recommended them to clean regularly after we try to stop the rust.

I'm not sure if using filiform corrosion and reducing the humidity would be beneficial to the bread, so I don't think that's a viable option. By sealing the surface of the steel panels do you mean applying another coating of something that doesn't rust as easily in this situation over the rust patches?

The Al channels or angles as I call them, are fastened to the actual panel itself on to the top and side panel, to hold the room together and to cover the cuttings.

The panel isn't scratched (it's pretty hard to scratch it anyway) but it might be the ends of the panels where we cut it which is being exposed. That shouldn't be a problem either anyway as I've sealed the channels with silicon. Shouldn't this in practise, prevent the steam from seeping into and behind the channels?

I mean rust when I said scraping off the residue. Is this naval jelly available anywhere? I'll read up on the links you provided and maybe do further research into this. It definitely will help.

Thank you, Astronuc.



Staff Emeritus
Science Advisor
If one cannot reduce the humidity and temperature, which is apparently inherent in the process, then the best solution is to separate (isolate) the Al channels from the steel, i.e. break the galvanic circuit.

I believe Naval jelly is available world wide. It appears that Loctite products are available in Australia.
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Science Advisor
Homework Helper
Astronuc said:
If one cannot reduce the humidity and temperature, which is apparently inherent in the process, then the best solution is to separate (isolate) the Al channels from the steel, i.e. break the galvanic circuit.
Or replace the AL channels with powder coated galvanized steel(like the panels) and use stainless or powder coated steel rivets and/or screws.

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