I forwarded your query to our conservator and she had the following to say:

"Why are they excavating without access to some sort of conservation
advice?  After all as we all know, excavation without conservation is
vandalism.  The normal process would be to x-ray the ball of nails to see
if there is any sound metal.

The cement mixer technique will damage sound metal (if there is any left)
and won't remove or stabilise the corrosion.  Chlorides may be an issue
too.  The corrosion layers can be analysed to give an accurate picture of
the conditions on the site ie how often the floods came through.

If the nails are important enough to be cleaned then they deserve
conservation to ensure their future survival.  In the US the American
Institute for Conservation has lists of private conservators all over the
country.  Their web site is http://aic.stanford.edu/   The US National
Parks Service will also have useful advice in their conserv-o-grams at
http://www.cr.nps.gov/museum/publications/conserveogram/cons_toc.html and
the conservation staff there can probably help too."

Hope this helps

Leah



Dr Leah McKenzie
Manager, Heritage Approvals and Assistance
Heritage Victoria
22/80 Collins Street
Melbourne VIC 3000