Dear Brian:
“
The installer cannot explain this and thinks the granite is defective.
”
Oh boy, now the granite is defective!!! That's a good one, alright!
Without actually seeing your stall, m only logical conclusion is that water, somehow, from somewhere, finds its way behind your slabs. Of course, the application of an impregnator (which is never good idea with stones installed in a wet environment), made so that the drying is much more laborious and may also have contributed to create those mysterious darker spots.
Check thoroughly all grout and caulk lines for possible entry by the water. Address any possible problem, let your stall dry thoroughly (hoping that also the darker stains will disappear) and then start using it again.
May I ask you now to please read and e-sign our Statement of Purpose at:
http://www.marblecleaning.org/purpose.htm?
Ciao and good luck,
Maurizio Bertoli
Article ID: 967
Created On: Sun, Dec 30, 2007 at 8:59 PM
Last Updated On: Sun, Dec 30, 2007 at 12:00 AM
Authored by: Maurizio Bertoli [mail@mbstone.com]
Online URL: https://marblecleaning.org/knowledgebase/article.php?id=967