Go to the "stained glass and mosaics forum", all the information you'll need you will find there. Good luck! Ramona Here is a link that might be useful: stained glass forum

To me mottled grout is not acceptable if you're paying for the installation. I agree with lisadlu that you can get mottled grout from improper mixing of the grout. I believe you can also get mottled grout from excessive water usage during cleanup which can saturate some of the grout. One other possibility (I think I've read somewhere) is a problem with the grout itself. Do you know what grout was used (manufacturer, etc)? I would speak with your tile installer ASAP and not pay for the work until the issue is resolved.

there have been various questions about this and whether sealants actually poison the water for birds. in so far as needing it to make the piece water proof, thats not required since cementious products are naturally hydrophobic and grout is cementious. So no it won't rehydrate as long as it is properly cured before wetting. I hope that helps...

Your mortar mix recipe of Portland cement and sand is thinset, so it would work just fine. It's what Riana uses to make and grout all her mosaics. You're new so you may not know "Riana". Four of us forum members took her workshop last spring in Puerto Vallarta, Mexico. Her website is: Riana