Lawrence F. London, Jr. lflondon at mindspring.com
Wed Dec 12 14:09:48 EST 2001

On Wed, 12 Dec 2001 15:30:01 +0800, Bob Howard
<rmhoward at omninet.net.au> wrote:

>Michael Dean wrote:

>> Can somebody explain to me why --"Never use lead head nails as fasteners on such a roof; alternatives: stainless steel screws, also galvanized screws and nails with neoprene washers"

>Corrosion is the short answer -  Lead and zinc have different electrical potential and when water acts as a conductor between them an electric potential is set up and one will corrode
>the other. 

Galvanized roofing and leadhead nails have been used together for over
half a century without corrosion problems and roofs that leak. As far
as I know there is no electrochemical reaction between the two that
would adversely affect a tin roof. 

>This is a general problem with most metals. It is generally unwise for different metals to be in contact especially where there is a risk of water being involved. (Tho' I'm
>not sure about why stainless steel is OK on galvanized roofs %-)

These screws are separated from the roofing with a neoprene washer
which seals the nail hole and the SS won't rust anyway and (I assume)
should not react with the electroplating on the steel roofing.

L.F.London ICQ#27930345 lflondon at mindspring.com
http://www.ibiblio.org/ecolandtech  london at ibiblio.org

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