In laying up the stones for your chimney, remember that it makes no
difference how rough and uneven it is upon the outside. The more uneven
the outside is the more picturesque it will appear, but the smoother and
more even the inside is the less will it collect soot and the less will be
the danger of chimney fires. Lay your stones in mortar or cement. See that
each stone fits firmly in the bed and does not rock and that it breaks
joints with the other stone below it. By breaking joints I mean that the
crack between the two stones on the upper tier should fit over the middle
of the stone on the lower tier; this, with the aid of the cement, locks
the stones and prevents any accidental cracks which may open from
extending any further than the two stones between which it started. If,
however, you do not break joints, a crack might run from the top to the
bottom of the chimney causing it to fall apart. Above the fireplace make
four walls to your chimney, as you did with your stick chimney (Fig. 271),
and let the top of the chimney extend above the roof at least three feet;
this will not only help the draught but it will also lessen the danger of
fire.