I'll offer my humble opinion.
1. Working in full sun w/make the adhesive/grout dry out too quickly. If you can build yourself some kind of shade over your project, it would be best. If that's not possible, spritz it often w/a little water to keep it from drying too quickly.
2. WHEN I am not so anxious to get to work on clay, I use Quickcrete brand of masonry/concrete sealer - it's a water-based sealer. Weldbond is good for inside sealing, not outside cuz it re-hydrates.
3. Thinset is best.
4. MAPEI brand has mortar (UltraFlex 2) and grout (Keracolor). For outside projects, I use the mortar for both adhesive AND grout. It's a terrific adhesive. I have also used the MAPEI sanded grout for outside projects successfully. Hope this helps.

Crystal, I have not completed a project outside in the sun but plan to soon. I have a new concrete bench and when it is cured, I'll work on it in place - too heavy to move inside. But it will be a relatively small project. This will be my first project to use thinset.

I have made several terra cotta birdbaths. I do these inside. I start by sealing them with diluted Weldbond. Then I paint the base with acrylic paint just to provide a white base for glass; you won't need to do this if you use plates. After I glue my glass on and grout, then I seal the entire dish with H&C concrete sealer. On my terra cotta dishes I have used E6000 and Weldbond for adhesives, but think E6000 or the thinset is best since these are usually put outside. I have had very good luck with E6000 on items for outside.

I would worry if you are doing this outside that the Weldbond would rehydrate if it rained before complete. so maybe sealing it with the concrete or terra cotta sealer would be best.

I'll be anxious to hear what others advise you too since I am new to thinset. Have you read the advise I got on my query: Outside Tiles and Thinset Questions?

*Sigh...
I know those of you who have been doing this awhile probably get tired of the same questions and I don't mean to be anal but I still get a little confused on the outside stuff. Some of you say "thinset" - is that the same thing as the Mapei Ultra Flex II AND if you use the Mapei, do you still have to seal it with a masonry sealer?

The info on another post about not using plates that were porous on the exposed edges sure got my attention, I used some plates like that on one of my stepping stones. :(

Lilym, I was advised by the concrete statuary manager to seal my mosaics with a concrete sealer. He said they seal everything they paint, stain, and mosaic.

Lilym, Does it freeze hard in zone 8 where you are? If you are concerned just take the stone inside during cold snaps. I use porous plates on my stones but I am in zone 10 so the yard art only needs to come in off and on during hurricane season tho the stones stay out as they aren't prone to blowing away.

p

We don't have prolonged freezing so much but it does freeze hard sometimes. We have 2 hardware stores and Walmart here but none have a sealer. The one I went to today only has Thompson water seal.

Small town living has some advantages but there are definitely some disadvantages, like finding stuff you need!!! Lowes and Home Depot are about 30 minutes away, can I get a sealer at one of those places?

I am making another stepping stone for a gift and have another to sell but I don't want them to come apart come winter.

What brand sealer do you use and where do you get it?

I use H & C concrete sealer purchased at Home Depot. I think any of the paint stores - Sherwin and Williams, Benjamin Moore carry it too or something similar.

Thanks, at any of the places I have looked so far the salesman looks at me like I had 2 heads. I'll check HD and Lowes the next trip out of town.

bump - good info

OH, yes, good info! Especially with good outside
weather coming!