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Corroding
Corroding  

Corroding2
Corroding2  
I have a strange situation going on in a residential environment. The issue relates to an unsolved and agressive aluminum corrosion situation.

I live in Florida and as such, most houses have hurricane shutters that are mounted over openings and there are mounting tracks that are made of aluminum. Also, the bottom tracks of sliding glass doors are made of aluminum.

I have serious and aggressive corrosion of the outside track of the slider (the one the screen slide on - not the tracks the doors slide on that are farther in). Also, the "F" tracks that the shutters bolt on to are corroding. The screen track is unpainted, but the shutter track is painted.

The corrosion has been going on for about 18 months. It was most noticeable when I got concrete pavers installed on the deck where the pool is (all the sliders are corroding).  This is a very standard installation in Florida.  The pool was also converted to salt water (very common in Florida) and no salt water gets on the aluminum.  The aluminum is powder coated except for the tracks of the sliders.  Also, there is an aluminum fence around the pool which touches the pavers and is not corroding.  Only the lower areas under the sliders.

What is intersting is that there are elevated tracks for shutters on the windows. But those are NOT corroding. Only the ones lower to the ground (sliders) are corroding.

This never happened before the pavers were installed. However, these pavers are very common in Florida and this installation is frequently done. Also, the aluminum fence around the pool is also touching the pavers and is not corroding. Only the areas next to the house.

I have had 7 contractors look at this and NO ONE has ever seen anything like it.  But everything about my house is standard which is the same as thousands of others in Florida.

Answer
Mitch,  I fear I am also at a loss as to the cause.

I've asked several others for input.  We all know that there are galvanic reactions between dissimilar metals.  Most of these manifest as pitting or erosion of one or the other materials.  Yours seems to be supporting  a crystalline like growth.

I did find some similar growth at this site:
http://en.wikipedia.org/wiki/Aluminium_oxide
They don't really discuss cause or prevention.

I know from experience that mortar and concrete will discolor and affect aluminum even if anodized.  One learns to respect these issues.  Here is an article about protecting aluminum and working with other materials:
http://www.cement.org/masonry/cc_al_frames.asp
I liked this line in particular:
"Two coats of bituminous paint or zinc chromate primer are often used in severe applications to provide separation of the aluminum from the cement-based products. A light coating of petroleum jelly painted onto the surface of the frame is another way to provide temporary protection to the finish during construction."

Another article discussed that the Ph problem is exacerbated with calcium chloride.  Perhaps the pavers had a heavy dose.

As to corrective measures, I think I would remove the pavers in contact with the aluminum.  Coat the underside of the aluminum with several coats of bituminous paint and use a tar paper type separation to prevent the pavers touching the aluminum.  Make sure that water does NOT stand or contact the area (I know, it rains every day there <grin>}.  Just make sure that it has good drainage and every opportunity to dry when wetted.

I'm sorry I don't have any better information.  County extension agent? Local code inspector?  More for their information, background, and possible other experience with anything similar.

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Dan Griffin

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I can answer almost all questions related to the total construction process. My expertise is in commercial construction, though I can field most any residential question. I have hands on experience in concrete, heavy equipment, masonry, all phases of carpentry, interior finishes, and I am fairly strong in mechanical and electrical.

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I have over 20 years experience as a commercial carpenter and commercial construction superintendent. I have another 20 years experience in facility management for a major school district.

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My favorite hobby for he past 12 years has been singing bass in a The OkChorale men's barbershop chorus and the Mature Moments quartet.

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I hold a Bachelor's degree in English and Math. I have completed many continuing education hours in the building trades. I hold a Master Carpenter card from the AGC, Associated General Contractors.

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