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Old 09-25-2017, 01:44 PM   #23
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

Join Date: Jul 2004
Location: Nashua, NH
Posts: 12,589
To be fair, I don't do this much, but I talk to lots of people, so take this with a grain of salt. I'd use the same trowel, then flatten the notches, then set the tile. Essentially, it should keep the tile at the same level as the surrounding ones IF you've set them properly. When setting a tile, two things are critical...getting as close to 100% coverage as possible, and keeping the spacing and plain so they are all even with minimal to no lippage. With smaller mosaics, you probably want to use something like a grout float to press them into place, otherwise, if you do it by hand, with all of the smaller pieces, things tend to get wavy. If the glass is at all translucent, if you have good lighting, you'll be able to see when you've embedded them well.

Notching the mortar produces an even coat, which allows you to keep things properly aligned once bedded. To achieve 100% coverage (or as close as you can get), you will have spread all of those notches out even so the depth is consistent...with a small mosaic, especially glass, it tends to work best if you flatten them first. When setting a larger tile, you wiggle it back and forth across those notches, flattening them in the process and spreading the thinset into a single, even layer. It's impossible to tell when doing this to a solid tile (well, you can peel it back up to check coverage once in awhile and that is a good practice), but you can't tell directly by seeing through the tile. You can with a glass tile. If the tile was clear, it would be very obvious if there was an air bubble, or void somewhere underneath.

It is critical to only spread your notches one way, otherwise, you won't leave a path for air to escape when collapsing the mortar ridges during the setting process which promotes voids.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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