The theory is that a thicker stone holds heat better, which is why many bakers seek out the thickest baking stones they can find. I was pretty happy with the way the pizza baked on my single layer of quarry tiles, but wondered if a double layer would be better.
Again, I preheated the oven for an hour. At the 45-minute mark, the tiles were at 525 degrees and at one hour, it was at 549 degrees. Slightly lower than when I tested the single layer at the same interval.
It took me just a little while to figure out the answer to both of those questions.
The difference wasn't the thickness of the double layer - it was the oven going through its heat cycles. So whatever slight difference there was in baking could be attributed to the oven.
Since I had nearly identical results baking on the double layer as when I baked on the single layer of tiles, there's no benefit that I can see in stacking the tiles, and a whole lot of downside, including the need to arrange 12 tiles instead of six.
To mitigate my annoyance with stacking tiles, I bought a 3/4 sheet pan to hold them. That worked to allow me to take them out all at once, but they still shifted around enough so that if I was placing the tile-filled pan in the oven, I needed to adjust the tiles once the pan was in place.
The benefit to using the pan was that it caught drips and spills that fell between the tiles. But the real downside was the ghastly scraping noise it made whenever I put the pan in or took it out. If I ever go back to using quarry tiles, I'll opt to use six tiles and arrange them directly on the rack.
But how will these tiles far compared to stones products that are made for pizza? Don't worry, we're getting there.