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Max1119 05-02-2008 07:11 AM

What type of metal to flash chimney and masonry wall?
I read somewhere that aluminum flashing is not good around masonry and chimneys because the alkali in the masonry corrodes the aluminum. Has anyone experienced this to be true ? If so, would painted aluminum alleviate this problem or is there another lower cost metal that works well for this purpose? (copper, etc. is not in the budget) Thanks in advance for your advice:)

Brik 05-02-2008 08:31 AM

Lead is often used. Not sure this is a modern practice as I have only worked with old lead flashing set into the masonry when the chimney was built. I think this is called counter flashing and is used with step flashing when roofing.

Ed the Roofer 05-02-2008 09:27 AM

That is supposedly true. I have read it in roofing and sheet metal and masonry manuals, but have never run into it in person. Maybe someone else has, but I have been roofing since 1978, so I would suppose that I would have run into it by this time.

Two of the villages around me even have that caveat listed in their building code guidelines.

If I do use Aluminum for my Counter-Flashings, I also use a seperator between the brick and sheet metal, such as Grace Ice and Water Shield. It is based on the customers budget and end resultant expectations. When I do use Aluminum, I use the .032 versus the thinner trim coil stock though.

The biggest problem, besides improper installation methods on chimney flashings that I see, is the usage of the tinner guage metals, which oil can and look all distorted, plus they do not have the rigidity of heavier stock to properly bend and insert where required to do so.

To this date, I have never seen any situation, Ever, where the masonry components have eaten through or degraded the Aluminum Flashings in any manner.

I have seen Galvanized flashings "Rust" completely through though.

I have also seen others use Aluminum Step Flashing Baby Tins with Copper Counter Flashings and the aluminum step flashings were eaten through as if eaten away by an acidic solution, which occurs due to the Galvanic Reaction.

But, just to be on the safe side, I always adhere the Grace Ice and Water shield around the entire brick masonry structure first, prior to mounting the sheet metal to the structure.


Brik 05-02-2008 11:04 AM

Thanks ed for clarifying - I have only done a handful of roofs. I did a tear-off/re-roof for a pastor in FL after Katrina came through. It was a straight forward job, one valley, ranch house, not a super steep pitch. Had a brick chimney for furnace I would surmise. Was on gable end so no cricket. It had lead counter flashing set into the mortar joints. We were able to peel it back, roof and step flash and push it back into place. The lead was in good condition so no need to replace it.
We used the grace in the valley and bottom edge as well as around the chimney as you suggested. In a warm climate I'm not sure as why the grace shield was specified but was on site and we installed it. I think the insurance company may have specified its use but I'm not certain about that.

Mike Swearingen 05-02-2008 09:58 PM

I'm not a pro roofer, but I had aluminum step-flashing with aluminum counter-flashing installed over it around a triple-flue chimney (two woodburning fireplaces) on our A-frame when it was built in 1977. The exposed counter-flashing was primed and painted, and we have never had any problem whatsoever.

the roofing god 05-02-2008 10:28 PM

flash the perimeter with ice shield 1st,like this;[1].jpg
then you`ll have no problems

Max1119 05-03-2008 05:58 AM

Thanks for the responses. Alot of really helpful info.:yes: I will use the ice/water shield and go ahead with the flashing. Thanks again

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