This was in an email sent to members of CMA (Contemporary Mosaic Art) website…
A message to all members of CMA
CMA Member News Reporter
Submitted by Tricia Huffman
May 14, 2011
Since this is the finishing touch to your hard work, I am expanding on the issue of grout issues from last report to address some questions that came to me as a result.
2. Concrete substrate had not fully cured or had a moisture vapor issue prior to adhering mosaic.
3. Water used in mixing or cleaning the grout was high in chlorine or had a high mineral content.( Pond water or home water softeners and city water that is heavily chlorinated or has a high mineral content can contribute to efflorescence.)
4 Temperatures were too cold while grout was curing.
5. Grout joints were wiped excessively during initial cleanup.
6. Standing water was left in empty grout joints prior to
7 Tile was especially dense and nonporous.
8 Grout was prematurely exposed to heavy amounts of water before it had a chance to cure.
Always consult manufacture instructions for your particular needs.