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letter 38492

Reactions between Aluminum and Lime

A discussion started in 2005 & continuing through 2017


Q. I have a question, when our aluminum tank coverings for upright storage tanks were exposed to Lime from a cement plant they all turned black. What is the reaction here and what if anything can we do to protect the tank coverings?
Do we need to replace the aluminum with some other covering? Can we coat the aluminum with something?
This is the first time we've run into this problem and have several hundred thousand dollars in material at stake.
Any comments would be greatly appreciated.

Gord Ferguson
insulation - Toronto, Ontario, Canada

simultaneous (2005)

A. Lime absorbs moisture from the air, creating hydrated lime [linked by editor to product info at Amazon] with a pH of 12.4, which caustic etches the aluminum. This is the same reaction as with fresh concrete. The dark color is from hydroxides of alloying elements in the aluminum, impurities in the lime and air pollution.

I suggest pressure washing the aluminum, then applying a glossy coating for easier washing and to help shed dust. A polyurethane paint or varnish over an aluminum-compatible primer should work. A water-soluble wax would be less expensive but require more frequent re-application.

Possibly, the cement plant will assist with costs & limiting dust emissions. Lime dust isn't much of an environmental hazard, but can be a serious health hazard. OSHA has an 8-hour worker exposure limit of 5 mg per cubic meter for CaO dust. I would expect a similar limit in Canada.

Ken Vlach
- Goleta, California
contributor of the year honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.

A. It sounds like the aluminum was etched and smut formed. Lime will form an alkaline solution, and a sufficiently alkaline solution will etch the aluminum surface. Significant etching leads to smut.

While you could paint or treat the aluminum, I'd work on preventing the lime from making its way onto your tanks in the first place.

Christian M. Restifo
- Pittsburgh, Pennsylvania

A. I assume that your tanks are aluminum, if so the lime is causing them to react. This could mean that the tanks are oxidizing or undergoing a similar reaction on the surface.
If you are truly worried over protecting these tanks I would suggest looking into getting the tanks cleaned and have a epoxy primer and a urethane paint applied after they are cleaned.

Marc Banks
Blacksmith - Shiloh, North Carolina

A. In your case the biggest problem is that the corrosion has already started. There are several good vapor corrosion inhibitor (VCI) coatings that will stand up to the lime dust and stop the corrosion process. The VCI coatings can usually be applied right over the current damage because they will 'soak' through the corrosion and passivate the metal from further damage. The VCI coating can be overcoated, if desired.

Grady Knight
- Colville, Washington


Q. I have lacrosse goals made of aluminized metal in the form of 1-1/2" pipes. In order to make them stronger and keep them from bending and breaking, I wanted to fill the bottom portions of the pipes with cement. Will the lime from the cement eat and destroy the metal or just turn the inside of the pipes black?

Joseph Gephart
- West Palm Beach, Florida

A. Hi, Joseph. Although the word 'aluminized' may have a more general meaning to some people, to many readers here it has the very specific meaning that the pipes are steel that has been hot dipped in molten aluminum to produce a sacrificial coating. So, assuming these are steel pipes, I don't think the attack of the concrete on their aluminum coating should be a significant problem for a non-critical application like a goal post. But it is frowned upon and certainly would be no good for a nuclear power plant :-)

If the pipes are made of aluminum, I wouldn't do it. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

January 19, 2009

Q. What is the chemical formulae for the reaction of Lime (with a pH greater than 12) with aluminium in aluminium alloy.

There will be alloying elements in the alloy which includes, Iron, Copper, Tin etc.

The greatest reaction should be the aluminium with the calcium hydroxide.

Thank you, pjm

Peter Moore
- Sydney, NSW, Australia

March 9, 2009

A. I know that when aluminum reacts with lye, the product is sodium aluminate, so that when calcium hydroxide reacts with aluminum, I'd expect calcium aluminate. Hydrogen is the by-product.

I plan to deliberately apply calcium hydroxide as limewash to the AAC house I want to build. Aluminum flashing, windows, etc. are RIGHT OUT...

Markian Gooley
- Hawthorne, Florida


Sodium aluminate

Calcium aluminates

A. Hi. Calcium is very active and certainly will not be produced as a free-standing metal from a reaction of this sort, so Mark's reply above sounds correct to me. Please see the Wikipedia articles on sodium aluminate & calcium aluminate to learn that aluminates are generated in many different forms; and the temperature and degree of hydration probably lead to very complicated reactions, but it can probably be written as approximately:
2Al + 2Ca(OH)2 + 6H2O (l) ----> 2CaAl(OH)5 + 3H2^ -- in other words, aluminates and hydroxides of various forms plus hydrogen gas.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

August 24, 2014

A. If you did already know, Al is an amphoteric (soluble/reactive in both Bases or in Acids) element, as is Zn.

*Bases do act like a "catalyst" in "Aqueous/moist environments" on the amphoterics like Aluminum.

** Hydroxide ions of bases, as a starter of reaction, do attack at the unstable passive oxide layers of Aluminum, and from the weakest oxide layer spot it starts dissolving in water through ion complex. At this pit hole, hydroxide ion of water attachs to the de-oxidized aluminum pit and forms a jelly-like, sticky, viscous insoluble Aluminum hydroxides/bohemite together with hexegonal calcium/sodium-katoite (depends on the base used)

***Here are reaction/molecular substitution phases together with their inter phases:

Ca + H2O >> CaO + H2 (CaO Unstable Reactive)(I)

CaO + 2H2O>> CaOOH(-) + H(+) (CaOOH Unstable Reactive) (II)

At this point reaction can go in 2 different ways:

a. Ca(2+) + OOH(+) + H(+) >> Ca(2+) + H-O-OH >> Ca(OH)2
b. CaO + OH(-) + H(+) >> CaO-H(+) + OH(-) >> Ca(OH)2

CaOOH(-) + H(+) + H2O >> CaOOH(-) + H3O(+) (III) >> Ca(OH)2 + H2O

Ca(OH)2 + Al(s) + 8H2O >> Ca3Al2((OH)4)3 + 6H2 (IV)
Note: Ca3Al2((OH)4))3 is called as KATOITE and is stable.
As you see here the Aluminum Hydroxide (Boehmite) diluted in water (Al(OH)4 ion) in basic conditions and then made hexagonal crystal complex with calcium ions which is Ca3Al2((OH)4)3: the Katoite

*Active Lime: Calcium Oxide (CaO)dust in non-moisture environment has no meaningful corrosive effect on aluminum. But under moisture conditions, even under atmospheric moisture, Active lime thermodynamically (exothermic reaction) dissolves in moisture (water) resulting with its base which is Calcium Hydroxide (Ca(OH)2) and this base reacts with passive outer oxide layer of Aluminum. As the Calcium Hydroxide opening/striping the oxide layers of Aluminum, Water attacks to the oxide layerless bold aluminum pits and forming jelly sticky white colored Aluminum Hydroxide precipitate.

Here we openly see Ca(OH)2 acts like a 'catalyst/catalysor' paving the way for H2O (moisture/water) to attach to stripped aluminum in Basic conditions.

**Normally this jelly-sticky precipitate of aluminum produced at the pit of oxide layer of aluminum acts like inhibiting the process that blocking contact/impact of both Ca(OH)2 and Water to the surface pits of aluminum. But this valid for the conditions that when Ca(OH)2 amount is too little.

As long as the basic terms of environment continue (that means big amounts of Ca(OH)2 and/or continuous addition of Ca(OH)2 to the system) insoluble aluminum Hydroxide precipitation will not settle down but will be dissolved in water ionically. Let us see how this happens:

Al(OH)3(aq) + Ca(OH)2(aq) >> Al(OH)4(-) + Ca(OH)(-) + H(+) + OH(-) (I)

Al(OH)4(-) + Ca(2+) + H2O + OH(-) >> CaAl(OH)4(+) + OH(-) + H2O (CALCIUM ALUMINATE ION)

let's get the balance:

it is 3 times Ca(2+) and 2 times (~twice)Al(OH)4(-) ion

3Ca(2+) + 3((Al(OH)4)): (6+) --- (6-)

>> Ca3.Al3(OH)12 >> Ca3(Al(OH)4)3 (unstable)


3Ca + 2Al(OH)4 + 8 H2O >> Ca3Al2((OH)4)3 + 6H2 >> Ca3Al2(OH)12 + 6H2



Ali Baris KAPLAN
Liquid Propellant Rocket Engine Designer - Istanbul, Marmara Region, Turkey

August 2014

thumbs up signHi cousin Kaplan. Thanks for the detailed and exacting answer!


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

November 17, 2015

Q. I have aluminum sliding glass doors sitting on concrete that leads to a step-down sunroom. The sunroom is not air tight and gets hot and humid in the summer. The aluminum bottom track is corroding and forming white beads of residue that seems to be acidic. I've been told this may be a chemical reaction of the lime in the concrete coupled with the moisture in the air seeping through to the aluminum track. It is getting to the point I can hardly slide the door. I want to replace the door but I'm afraid a new aluminum door and track with do the same thing over time. Putting a barrier might be an option, but the doors have to be screwed into the concrete allowing seepage anyway. Vinyl is an option but a replacement would be 6" wide and I only have 4" so the extra would protrude into the sunroom. Another option is wood French doors but I would lose space from opening the door. Has anyone encountered this and what would be a good solution?

Deborah Turner
- Clearwater, Florida USA

How to generate hydrogen gas for AAC Block production

May 20, 2016

Q. In production of AAC Blocks (light weight concrete blocks), aluminium is used for generation of Hydrogen gas. I want to know the details of the chemical reaction, conditions for generating proper gas, whether hydrated lime can be used in place of quick lime...

Jagannadha Rao Yeluri
Enterprenuer for AAC Block making line - Visakhapatnam , A.P. India

May 2016

thumbs up signHi Jagannadha. It seems that you're not asking for generalized science info about chemical reactions ... rather, you're asking a manufacturer of AAC blocks for detailed information on what you need to do to compete against them and take some of their business :-)

Here is your posting. I'm not expecting a lot of response -- but maybe people will surprise me :-)

Good luck,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

June 15, 2017

Q. I put ag lime next to my above ground pool will this cause it to rust?

John Barney
Carpenter - Crown point Indiana

June 2017

A. Hi. Lime will probably not hurt steel if that's what your pool is made of. If your pool framing is made of aluminum, it can't rust since only iron/steel can rust, and just having lime in the general area probably isn't a major issue. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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