Brick flues for hothouses

2109. The sides of common flues are commonly built of bricks placed on edge, and the top covered by tiles, either of the full width of the flue outside measure, or one inch narrower, and the angles filled up with mortar, which Nicol prefers, as neater. Where a stone that will endure fire-heat without cracking is found to be not more expensive than tiles, it is generally reckoned preferable, as offering fewer joints for the escape of the smoke. Such stones are sometimes hollowed on the upper surface, in order to hold water for the benefit of plants in pots, or for steaming the house.