Tom,
Very interesting! Do you have any data on the TYPE of brick? I can understand that some brick will more readily absorb water than others, depending on the type of clay used, and the firing process. Some clays are very expansive. The firing process should stop that characteristic, but, may not.
Also from where (locale) were these bricks sourced?

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags