I have a marginally legitimate question again. 
 
 Our local historical society's HQ is in a 1740s farm house with a  sawn 
cedar shake roof, which as I remember is about 23 years old (I used to be  on 
the board, but haven't been in decades).  I am told by a friend now on  the 
board that they are thinking about power washing the roof to get  rid of 
whatever growies are growing in it, which makes me uneasy.
 
 What is the current state of the art Histo Presto thinking on  maintenance 
of such a roof, and am I correct in worrying that pressure washing  will 
drive moisture further into the shakes?  Are there chemicals they  should use 
or avoid in power washing?
 
Thanks,
Ralph (9 days prostate-free)

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