permaculture

[Bob Howard <rmhoward@omninet.net.au>]

Michael Dean wrote:

> Howzit,
>
> 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"
>
> Cheers Mike.
>

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. 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 %-)

Bob