A concrete slab 4 to 8 inches thick with the bottom 4 to 6 inches below the surface provides a sufficient foundation for medium-sized structures where frost is negligible and the soil is well drained and firm. If the soil is not well drained a 6- to 8-inch layer of stone, cinders, or sand should be provided under the slab and the surface of the immediate vicinity graded or otherwise protected from water. It is advisable to use ¼-inch or ½-inch reinforcing rods, 6 inches apart in both directions, one-third the distance from the top in slabs for all but the smallest fireplaces or where frost is not severe.
Figure 43.—A, Ground plan of a stone fireplace that can be built in different sizes to suit the landscape; B, vertical-section sketch; C, the completed fireplace. The stones for this fireplace were picked up at "the swimming hole." About 8 bushels were used over a backing of concrete; 16 bushels would have been needed if the concrete had not been used. Gravel and sand were dug from the excavation. The chimney is battered 4 inches in the 24-inch height.
Heavy and expensive structures, especially those having tall chimneys, should have foundations below the surface affected by frost or erosion and strong enough to prevent settlement or cracks. Such a foundation can be made of concrete, with a liberal use of large stones for economy, extending under the whole structure, or be continuous walls with a footing similar to those used for houses. The advice and help of builders may save money in the construction of foundations of large expensive fireplaces, especially where climatic conditions are severe and the bearing power of soil is not known.
Cooking should be done over glowing coals, as flames and smoke smudge the utensils or even the food. When the wood is nearly charred, most of the smoke has been driven off and the chimney is hot enough to draw the smoke up the flue. All fires should be banked before they are left, to avoid setting fires. Banking can be safely and effectively done by raking the coals and unconsumed fuel into a pile on the hearth and covering the pile with a few inches of earth. Water thrown on a hot fire may result in scalds from the steam and may crack the fireplace.
Barbecue ovens are rather expensive unless for community use. Outdoor fireplaces, without or with spits for roasting, are frequently called barbecues in some sections of the country. For occasional barbecuing parties, a hole in the ground will serve. Dig a hole several feet deep and several feet larger each way than the size of the carcass to be roasted; then place stones in the bottom to retain the heat. A trench 30 inches deep, 36 inches wide, and about 10 feet long will accommodate about 400 pounds of beef. A fire should be built sufficiently ahead of time, about 3 hours, to heat the stones and bottom and accumulate ashes for proper banking. Have someone with previous experience operate the pit, because improper wrapping of the meat and handling of the coals results in poor cooking.