WSP - You probably have the correct or at least most commonly used hearth bricks already. Part of the confusion is that the terminology isn't always consistently applied & it's sometimes difficult to discern which sources can be taken as authoritative. I've spoken to a lot of refractory & chemical engineers and most will suggest that dense firebricks of about 30 - 40% alumina are ideal for pizza hearths. This is the same recommendation
that is given in the Pompei oven plans. A few e.g. traditionaloven.com
recommend 18 - 28%, but this is the really the recommended ideal for bread ovens. The concern for bread is that the extended contact period with the hearth may burn the crust with higher alumina materials that transfer larger amounts of energy for a given time.
Descriptive labels as opposed to percentages can be misleading though. In Bread Builders
, Alan describes standard dense firebrick as 25 - 28% and also refers to it as low duty. What he is calls medium duty firebrick (unspecified, but somewhere between 28 - 60% alumina) is described as being advantageous for pizza but warns that higher duty firebricks are more prone to cracking & spalling. It's unclear if he is referring to firebrick in the 28 - 60% range or just the 60%+ firebricks. My refractories handbook
(Schacht) classifies firebrick as 25% (low duty) 29% (med) 37% (high) and 42%+ as super duty. And again gives us a general rule that higher alumina bricks are more prone to spalling from thermal shock. So depending on who you are citing these categories overlap or may label the same product as standard, low duty or medium duty. Note that the common castable refractories that have similar thermal properties to firebrick e.g. Mizzou
can have alumina contents in the 60% range, probably making them better suited for the dome walls than hearths. Suffice it to say that almost everyone recommends 30 - 40% alumina for pizza hearths & that is probably what you already have.
Now, could you do better? There appears to be general agreement that the refractory tile floors are better. How much better? My sense is that this advice represents smaller, rather than larger differences. The common tile arrangement is to have a circular floor divided into four 90° quadrants. So being only four pieces it's easier to install & level. You attenuate a theoretical concern that if the bricks/tiles don't have good contact that heat transfer may be uneven. And there are less grooves for a peel to catch on and less edges that might spall or have accelerated abrasive wear. It avoids having to trim bricks to fit within the dome walls. And of course, it costs more. No free lunch for us.
And while almost everyone seems to recommend or prefer refractory tile over firebrick, it's all anedoctal. Firebrick is used industrially, they have to tell us what the composition is. It's difficult to come by technical data such as alumina content, porosity, thermal conductivity, etc for products like Biscotto di Sorrento
. You can reasonably infer that it performs well and is durable by the historical use in high volume pizzerias. And it's implied that the skilled Neapolitan oven builders have by experience come to select floor and floor bed materials that create a thermal equilibrium for the floor. But none of this is quantitative. If you find any quantitative data or scholarly research, please pass it along to the rest of us.
For myself, I wouldn't replace a firebrick hearth unless it was mechanically failing or had chronically bad performance. But based on the available evidence, anedoctal & otherwise, I'd prefer to put a refractory tile floor into a new build. And for a commercial venture, I'd hire someone knowledgeable like Marco to erect an authentic Neapolitan oven.