Remember, we have the oven built of red brick, there was a crack. When you are kindling from it stretched a thin trickle of bluish smoke. My grandfather made a special putty and filled her crack, the oven immediately stopped to smoke. Putty, as explained by the grandfather, not only resists high temperatures, but with its increase in proportion to increases its strength, acquiring the hardness of stone, and it does not crack.
I was taught to make the putty. You need to take the same amount of finely crumbled red clay and pure pine tar, add a little salt, mix it all up, then pour water and turn the mixture into a kind of test. Cracks, svyazannym this “test”, sealed tightly. Such a property of the putty makes it indispensable where the sealant is “dealing” with high temperature.