Bread-Baking Stone

As my bread tends to break open at the bottom, I asked some people for advice and the thought, I'd have better results with a "Baking-Stone". You can get them in Germany for a lot of money... and here you can get similar stones... they sell them as "Pizza-Stones".
This stones guarantee, that the heat stays solid, when the bread gets "shoot" in, so the dough gets firm before it can break open. The Pizza-Stones, so I got told, are to thin. They won't hold the heat very long... They are also too small for my two loafes that I mostly bake. The "Sauerteig-Forum" said, Fire-Bricks and Granite are the best choice: between 2 and 3 cm thick and as big as you need for your oven.
Well... I went into a tile shop and got a granite-tile. It is only 1 cm thick and 305x305mm square. BUT: it did the job:

Its only the natural stone, nothing added.
I baked yesterday with it and it worked just fine:
You put it on the lowest rack for enough "underheat". When the oven has the temperature you want, the stone STARTS to heat up for THAT temperature, so you need to keep it for at least another 30 minutes longer at... in my case... 250°C. BUT: you can turn the oven off 10 or 15 minutes before your baking time is finished: the heat of the stone will finish it.
If you have a thicker granite, you have to heat it up for a whole hour, but also can turn the oven off after 20 minutes or so. At least thats what they say. Best is always to try for yourself.
I got told, it is ok to spray cold water on the stone, when you shoot the bread in (which I did), but you shouldnt take it out and put it into cold water or expose it to other fast temperature changes. Than it might crack. Just let it cool down IN the oven, with the oven.