In a freeze-thaw area I would be hesitant to do anything wet-laid unless it is in a covered and protected area. Any moisture that gets in the “grout” lines or under the bluestone in the mortar will expand when it freezes and risks damage to the mortar “grout lines”, the mortar bond under the bluestone, and/or the bluestone (cracking, spalling). If the area is covered and not likely to have much snow or moisture on it during these cycles it may be fine. In my zone4 there are examples of wet-laid that lasts for a long time, but also many that don’t do well on wet horizontal surfaces. That being said, if you like the look or bluestone I would ask if they could also install that on a compacted base, screed sand or gravel, and sand or polymeric sand in between the joints. This would be more like a paver-type installation, has a little flexability to deal with freeze cycles without popping mortar, and would have a similar look to wet laid bluestone.
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Undermount cooler with removable lid
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