CAMP STOVES AND FIREPLACES

FOUNDATIONS

Fireplaces which are constructed of loose boulders (pl. I, fig. 1) require no foundation. The lower stones should be set into the ground approximately one-half of their depth.

All stoves and fireplaces of masonry construction should set upon a concrete or a masonry foundation.

The foundation may be of two kinds:

(a) A reenforced concrete slab which does not extend below the frost depth (pls. II, IV, and VIII).

(b) A concrete or masonry foundation which extends below the frost depth (pls. XI and XII).

In locations where it is not practical to construct concrete foundations, the grate shown in plate III may be anchored with a "log dead-man" as shown in figure 6.

The concrete slab must be properly reenforced with wire mesh or bars, in order to prevent any rupture from frost action. The foundation which extends below the frost line need not be reenforced, and may be constructed of stone, brick, concrete, or cement block, or any similar material which is available in the locality.

In constructing the foundation, a pit of the proper dimensions is excavated. The reenforced concrete "floating pad" should rest upon the natural subsoil. If any fill is necessary on which to construct the reenforced concrete pad, it should be limited to a few inches (otherwise another location should be selected), and this fill should preferably consist of masonry, although it may be laid "dry" if thoroughly compacted.

For the foundation which extends below frost depth, the bottom of the pit is filled with a mixture of concrete into which "spalls" may be thrown. The material is thoroughly tamped and the concrete constructed upon it.

The concrete mixture should be as follows:

(a) Where screened aggregate is used, the mixture should be one part cement, two parts sand, and four parts of coarse aggregate, graded to a size of approximately 1 inch.

(b) Where unscreened aggregate is used, the mixture should be one part cement, and six parts of pre-graded gravel with a maximum size of gravel passing a 1-1/2 inch screen.

If the fireplace is generally low, and there is no excessive weight at one end, which might cause the structure to settle unequally, a reenforced concrete "floating pad" is sufficient for all normal requirements (pls. II and IV). The average height of the low fireplace including this proposed foundation is approximately 24 to 30 inches. The resulting weight per square foot approximates 480 pounds. Average clay soil is capable of supporting approximately 1 ton per square foot, or four times this load. Inasmuch as the average site chosen for a fireplace is on the firmer soils, the normal weight is far below that which the soil is capable of supporting and therefore, the question of foundations in the majority of these fireplaces, even where extreme temperatures are experienced, is one of providing a footing which is properly reenforced near the upper surface (pl. IV, fig. 4) to allow for the heaving and settling of the fireplace as a unit.

In most of the larger camp stoves with a chimney, where excessive weight occurs at the chimney end, the foundation wall should extend below the frost line (pl. XI).

FIREBOX

The size of the firebox has a direct bearing on fuel consumption. In areas where fuel is scarce and charcoal is used, its size should be kept to the minimum dimensions (height 6 to 7 inches, length 18 inches, width 12 to 14 inches). It is also desirable when charcoal is used as a fuel, to so design the firebox that there is a small opening in the bottom of the firebox through which the necessary draft may be created, to cause the necessary combustion in charcoal. The firebox in the camp stove (used for cooking only) requires less width than the firebox in the fireplace (used also as a warming feature). The cooking surface should be of sufficient area (average area approximates 2-1/2 square feet) to accommodate at least a frying pan and a coffee pot. The area may be increased, as hereafter explained, if more cooking surface is required.

The size of the firebox is to some extent determined by the amount of surface which is desired for cooking purposes. In the larger unit, the dimensions will approximate the following: Height 8 to 10 inches, length 20 to 30 inches, and width 12 to 18 inches. The height is normally from 8 to 10 inches, inasmuch as the best cooking fire comes from the glowing coals rather than from a high flaming fire.

In order to procure increased cooking and warming surface and at the same time preserve the minimum dimensions of the firebox, a type of design may be adopted as shown on plate XIII, figure 3. The open area between the firebox and the flue virtually becomes a part of the flue, although it is covered with a solid plate, the surface of which is sufficiently hot for cooking.

The open end of the firebox should face the prevailing wind. The shape of the firebox is normally rectangular. Sides splayed to the front are of some advantage in the case of a warming fire; but they add to the difficulty of procuring and installing the grates, plates, and lining.

In all stoves and fireplaces the firebox should be so constructed that there is a slight slope from the back of the hearth to the front of the hearth, in order that any water which accumulates on the hearth will immediately drain out of the firebox.

Because of the fact that the ordinary kind of stone available for camp stoves and fireplaces is not resistant to sudden extremes of heat and cold without undue damage, the best practice is to line the firebox with fire-clay brick in order to protect the stonework against direct exposure to these extremes. In some instances, a lining of 10-gage sheet iron, made to conform to the measurements of the proposed firebox, and with a grating attached, is used in place of fire-brick. These combined grates and sheet-iron sides can be manufactured at small cost, and where the cost of procuring fire brick is abnormal, this type of lining is a practical answer to the problem of protecting the stone-masonry sides against injury from direct exposure to the fire.

Sometimes it has seemed desirable to construct a precast firebox of reinforced concrete, so that the firebox may be set into a space surrounded by stone masonry walls which forms the shell of the camp stove. The theory being that if the firebox is damaged by heat it can be removed easily and replaced by another firebox. This procedure does not seem to be a logical procedure for the reason that a firebox of a much more permanent character can be constructed of fire-clay brick as a permanent part of a camp stove. Concrete thus exposed to intense heat will undoubtedly suffer definite damage in a very short time.

Ordinary brick is sometimes used for lining some of the simpler types of fireplaces which are not intensively used and which are not doused with water. This type of construction is not recommended. In localities where lava rock may be procured easily, the lava rock lining is equally as acceptable as fire-clay brick. Ordinary brick will shatter and disintegrate if subjected to extreme and sudden changes in temperature caused by water dousing.

Fire-clay brick (sometimes called fire brick) is made from fire clay by what is known as a dry pressing process. In this process, 4 or 5 percent of water by volume is added to the dry fire clay which, when thus moistened, seems hardly damp. The thoroughly mixed fire clay is then formed into bricks under a pressure estimated to approximate 4,000 to 5,000 pounds per square inch.

Fire clay, from which fire-clay brick is made is defined by the American Society for Testing Materials as a "sedimentary clay of low flux content, and consisting essentially of hydra-silicate of alumina." There are at least six or eight distinct kinds of fire clay, having different properties with respect to chemical composition.

The standard size of fire-clay brick is 9 by 4-1/2 by 2-1/2 inches. There are four classes of fire-clay brick, classified according to heat resistance. The class commonly known as third quality fire-clay brick, or correctly designated as moderate-heat-duty brick (according to the standard definition), is generally used for lining fireboxes and hearths in camp stoves and fireplaces. The softening point of this brick is approximately 2,905° F. and its maximum expansion is one-sixteenth inch per foot at a temperature of approximately 2,200°. Concrete will seldom withstand a temperature in excess of 1,000° F. and the normal temperature in the average camp stove or fireplace ranges from 800° to approximately 1,500°. The coefficient of expansion of fire-clay brick is about one-third or one-fourth of the coefficient of expansion of iron. In decimal figures, this coefficient is 0.000005 for each degree centigrade.

Fire-clay brick is usually laid on its natural bed, but sometimes it is laid on side. In laying fire-clay brick in camp stoves and fireplaces which are exposed to the weather, the fire-clay mortar should be a mixture of fire clay with approximately 20 to 25 percent of portland cement by bulk. This mortar is "buttered" lightly with a trowel on the surfaces of the brick and should make a joint approximately one-sixteenth inch in thickness. If the fire clay is spread too thickly, it will destroy the strength of the fire-clay brick lining. This joint should be just as thin as it is practicable to make it.

The reason for keeping fire-clay mortar very thin on the surface of the bricks is because the fire clay used in the joint between the bricks is not as resistant to heat as is the fire-clay brick itself. The joint would, therefore, have a tendency to shrink and cause damage if the joint were even as thick as one-fourth of an inch. This thin joint is sometimes procured by dipping the fire-clay brick in fire clay of a rich, creamy consistency and pushing the brick into place by rubbing the top brick back and forth on the lower brick.

Many instances are observed in which apparent defective construction has not produced satisfactory results in the construction of the fire-clay brick lining.

For the best results, fire clay used to create a bond between fire-clay brick should be subjected to a temperature exceeding 1,600° to 1,800° F. in order to cause the chemical reaction required to make the joint permanent. It is doubtful if the heat produced through the normal use of any firebox is sufficient to cause the permanent chemical change necessary to produce the desired result.

The best results are procured in the construction of fireboxes for outdoor camp stoves and fireplaces when, to the fire clay, there is added by volume approximately 20 to 25 percent of portland cement or similar cement. The addition of this cement produces a "cold set", which the subsequent heat further fixes, with the result that this fire clay and cement joint creates a solid and permanent bond.

It is desirable, in any event, whether or not cement is added to the fire clay, to subject the lining of the fireplace to an intense fire for at least 4 or 5 hours. If fire clay is used without the addition of cement, this fire should be sufficiently intense and continued sufficiently long so that the inside surface of the brick shows evidences of starting to glow. Unless this procedure is adopted the joint will be damaged by rain and by freezing.

There are on the market air-setting, high-temperature cements which will create an excellent bond under a cold set. It is doubtful if high-temperature cements will be as permanent as the bond produced by a mixture of fire clay and portland cement or its equivalent, as above suggested.

The average mortar will not usually withstand any considerable amount of heat because of the content of lime which fluxes under heat and because of the content of sand which does not have refractory qualities to the extent required in these joints.

In filling the space between the back of the fire-clay brick lining and the face of the stone masonry shell or covering, the fire clay, properly moistened, should be mixed with pulverized calsined fire clay in the proportions of one part fire clay to two or three parts of the calsined fire clay. It is not recommended that this space be filled with pure fire clay for the reason that the natural fire clay will shrink to a considerable extent when subjected to intense heat. The fire clay should be mixed as above indicated with calsined clay because the calsined clay has been subjected to a considerable heat and will therefore not be subject to any considerable amount of shrinking.

The space between the fire-clay brick lining and the stone masonry backing must be completely grouted and thoroughly sealed at the top to prevent any water from entering. In some camp stoves where intense heat is developed, an air space between the fire-clay brick lining and the face of the stone masonry is provided. This method of construction is open to some question. Sometimes this air space is filled with powdered asbestos in order to further protect the stone masonry against intense heat.

It is also advisable to construct the hearth, or floor of the firebox, with fire-clay brick unless, as in the fireplace shown on plate VII, figure 6, the surface of the hearth is level with the surrounding ground, in which case it may be equally as well constructed of mineral earth or natural porous soil.

In the fireplace with closed back (pls. III, IV, V, etc.), the only real draft control is in the orientation with respect to the direction of the prevailing wind. A raised back somewhat improves the draft, and a movable solid plate may sometimes be used in connection with the raised back to further control the draft.

The chimney notch shown in plate VIII increases the draft by restricting the gases to a definite limited passage. The maximum control of draft is obtained where a chimney is used. The draft is further controlled by dampers in the doors at the front of the firebox and also by dampers in the chimney. The chimney may vary in height, as shown in plates X and XII.

The door on the front of the firebox may be of cast iron or sheet iron, in conformity with the materials used for the cooking top. Besides being hinged so that it can be fully opened there may be, as shown in plate XXII—A, figs. 3, 4, and 5, a small opening in the door to provide draft.

A draft control necessary to maintain the desired fire may be provided in one of three ways as follows:

A. By an ashpit under the firebox, on the front of which is a door which may be opened or closed to produce greater or less draft.

B. By an opening in the door as shown in plate XXII—A, figures 3, 4, and 5.

C. By a damper constructed in the chimney (pl. XXII, fig. 3), or by a damper constructed in the rear of the firebox at the point where the flue enters the chimney.

It is apparently necessary in some localities of extreme moisture conditions, and especially in high altitudes where much fog is prevalent, to procure a maximum draft by providing an ashpit under the firebox. The ashpit is not generally recommended nor usually essential in the average camp stove. It ought not to be constructed unless the requirements for maximum draft, to burn wood not thoroughly dry, make such an ashpit indispensable.

Under normal conditions, sufficient draft control may be had through the adjustment of the doors in the firebox. Sometimes the draft in the chimney is controlled by a pivoted iron plate on the top of the chimney. The value of this device is open to question. The built-in type of damper with the revolving metal shield (pl. XXII, fig. 3) is the most effective; but its operation is not fool-proof. No damper should be installed which does not leave a limited portion of the flue (approximately 35 percent of its area) free when the damper is practically closed.

TOP GRATE OR TOP PLATE

The top of the stove or fireplace may consist of a grate (simple bars or a fabricated grate) or a solid plate. In some instances, in place of a definite grate a heavy electric welded wire mesh is being used. This type of grate is less expensive than the iron plate. The solid plate provides better draft and a better control over the draft. Its use reduces the fire hazard and is sometimes necessary in certain locations where the fire hazard is great. In some States laws have been enacted making it compulsory to use on camp stoves a solid plate for the top of the stove and a door on the front of the firebox which at all times prevents any possibility for sparks to escape and cause a forest fire. In picnic fireplaces, except those used for warming purposes, the grate is generally adopted but in a few instances a solid plate is used. On camp stoves, where the camper desires to keep the pots and pans from smudging, a solid plate is generally used. In many instances, and where the use justifies the expense, a combination grate and plate top is used (pls. X and III—A).

In some fireplaces, a successful method of cooking is that of using a reflector plate of sheet iron or other metal, which can be stood at an angle of approximately 60° immediately in front of the opening of the fireplace, and supported by an arm which keeps the plate at the proper position in relation to the fire. This contrivance is often used in place of a grate or plate over the top of the fire, and it may be home-made or purchased from some supply houses with the necessary attachments to hold food which would otherwise be laid upon the grate or plate. This method of cooking avoids unnecessary burning of food and is almost as efficient as the method of cooking food over the top of the fire.

Where the combination plate and grate is used, the plate may be used over a part of the grate as shown on plate III—A, figures 1 and 3. Such an arrangement makes possible an area for warming and grilling, and also an area for frying and other cooking.

In instances where the plate is used to cover the entire grate, both the grate and the plate may be hinged as shown in plate X, figure 4, or both the plate and the grate may be attached by a chain to the sides of the fireplace (pl. VII).

The plate is, without a doubt, the ideal top for a camp stove where the stove is used for three meals during each day. In picnic areas, where the fireplace is used for cooking purposes, perhaps once during the day and possibly not every day, a grate or mesh is acceptable, although the extra work of cleaning blackened pots and pans is necessary. The fabricated grate or mesh (pl. VI) is much preferable to built-in bars shown in plate IV.

It is very important that the space between the bars in any grate be not too large, thus allowing small sections of meat to fall between the bars. The average acceptable space between bars is 1-3/4 inches. The use of separate bars, although not the most acceptable solution, is sometimes necessary where, either because of lack of funds or for other reasons a suitable fabricated grate or mesh cannot be procured.

The bars to be of proper strength should be approximately 1/2 to 3/4 inch square, or they may be circular, with a diameter of 3/4 to 1 inch.

The plate ought to be of sheet iron or cast iron. Ten-gage black iron or boilerplate offers a quick heating surface. Cast-iron plate, if too thick, usually heats too slowly. A normal thickness is three-eighths inch.

Considerable difficulty may be experienced because of the tendency of any top plate of sheet iron to warp and sag. This undesirable result is caused by the following conditions:

A. Using a plate of iron which is too thin.

B. Not using the necessary angle irons or other methods of reenforcing the top plate.

C. Making no provision for expansion at the points where the plate is attached to the masonry construction.

Removable cast-iron plates are not as practical as sheet-iron plates for the reason that the rough handling which is received by some of these movable tops will cause breakage. In all removable plates there should be one or more holes at some convenient location to facilitate handling. The cast-iron tops may sometimes be fitted with pot holes of various sizes, each of which is covered with a lid or sheet-iron plate, all of which must be securely anchored to prevent removal or loss. Such small movable parts are not entirely practical in the average campground and their use should be discouraged.

Steel plates should not be used because steel rusts easily when exposed to the weather, unless protected with paint and carefully maintained.

Flanges at the edges of the plates as shown in plate VIII, figure 1 and in plate XXII, figure 4 and extending entirely across the firebox will do much to prevent sagging. The problem of warping is one which comes from exposure to heat and is not due to any great extent to the inability of the plate to support itself. Proper reenforcing on the underside of the plate and correct attachment of the plate to the masonry sides of the stove or fireplace will overcome it.

A desirable method for attaching any plate to the solid masonry is to provide proper reenforcing members on the underside of the plate, the end of which will fit into a metal socket similar to that shown in plate XXI, figure 5, thus allowing for the necessary expansion and preventing any damage to the stone masonry at this point. Where bars are used, the ends of the bars should fit into pipe sleeves of somewhat large diameter and with ample clearance allowed in order to provide for the expansion (pl. IV, fig. 4). Provision may be made as shown in plate XXI, figure 5B, for the removal and replacement of bars which are broken or bent through careless use of the fireplace. Where bars are used in place of a fabricated grate, it is sometimes desirable to carry the bars in sockets entirely through the stone masonry wall, as shown in plate XXI, figure 5C. In cases where this method of construction is adopted, some provision should be made for locking the bars so that they cannot be easily removed. This is accomplished as shown in plate XXI, figure 5, section A—A. Attaching bars and grates solidly to masonry will break the stone. If a fixed grate is used, the grate may be so constructed that the corners will have bars which fit into metal sleeves as above described. As a matter of fact, the top plate and any bars should never be attached in a fixed manner to the top of the stone masonry. Suitable provision should be made to take care of expansion. Where the grate is removable it can rest on a base formed by the top layer of fire-clay brick as shown in plate VII.

The question of whether to use a removable or a fixed top has not been satisfactorily solved as a result of experience to date. The removable top increases the convenience of building fires and removing ashes. The fixed top on the other hand, is an additional safeguard against vandalism and otherwise careless use of these facilities.

Where a solid plate is used, especially in fireplaces, it is desirable that this plate be removable or hinged so that the fireplace may be used as an open warming fire during the evenings and on cool days at times when the fireplace is not in use for actual cooking purposes.

If the top is removable, it should be securely attached with a chain, anchored to the masonry, or to a post driven in the ground to a sufficient depth to prevent any removal of this feature.

Where a hinge is used for attaching the plate or grate to the top of the stove or fireplace, the type of construction as shown in plates VI and X is most acceptable. If the top grate or plate is to be hinged, this detail of construction should be solid, and of such a type that damage cannot be easily caused by careless handling. See detail of hinge in plate XXI, figures 2, 3, and 4.

As shown in plate IV, it is sometimes necessary to sink the grate or plate slightly below the level of the side "shoulders" in order to provide for the proper anchoring of the hinges or the bars. The elevation of the side walls may also give some small protection, especially to the fire when the grate is used.

In many camp stoves and in fireplaces with a solid top, an abnormal amount of heat is lost because it passes up the chimney. This condition can be corrected to a large extent by the construction of a proper damper in the chimney and by the construction of a shallow firebox with a larger heating surface, as shown in plate XIII. In some areas where the proper provision is not made to prevent an abnormal amount of heat from passing up the chimney, many efficient campers set some of the pots and other cooking utensils on the top of the chimney in order to take advantage of the heat at that point.

In most camp stoves and fireplaces the limited space on the top of the cooking surface is not sufficient to set all of the pots and pans in which food is being cooked or being kept warm. Additional space may be provided as shown in plates VI, VII, and VIII, with very little additional cost.

STONEWORK

There are many kinds of stone available in different parts of the country from which to construct camp stoves and fireplaces. This stone ranges from the "nigger heads" and boulders of the New England region to the lava rock of the Northwest and the Tufa rock of the extreme South.

The detailed design and construction of any stove or fireplace, of which various types are shown in the following plates, will vary with the kind of local stone which can be procured. The same design, built of volcanic rock, will take on a different texture and appearance from the one constructed of stratified sandstone or of boulders. The carrying out of each design in the materials available and in the most appropriate form must, to considerable extent, be left to the judgment of the local superintendent.

All stonework should be constructed as closely as practicable in accordance with the detailed drawings. A special effort should be made to procure an informal texture with stones laid on their natural bed in order to carry the horizontal effect (pls. XXIV and XXV). There may be rare instances in which the surrounding natural conditions require that the stone be laid to produce a vertical texture.

All stone before being laid should be free from any dirt or foreign matter and, unless the supply of stone is extremely limited, it is much better to select individual stones of the size and shape which will produce the required texture of stonework than to endeavor to use the large and the small stones as they are found.

Stones which are cut or broken are usually divided into two classes: (a) Stratified; (b) Unstratified.

The examples of stratified stone are sandstones, limestones, and shales. Igneous rock, granite, and lava are in the unstratified group.

Stratified stone (pl. XXV, fig. 5) is easier to lay than the unstratified stone (pl. XXIV, fig. 5), which requires a more careful selection to produce desired effect in actual construction.

Stone texture is an elusive element in design because so much depends on the skill of the workmen. A camp stove or fireplace must be practical in use, and it must be of appropriate design in mass and texture. The texture of the stone masonry is so frequently not well designed (pl. XXIV, and pl. XXV, figs. 2, 4, and 6), that its importance in the completed structure should not be minimized. Many of these features look like stone piles with no stability or like monoliths of mortar and stone with no surface texture.

Joints in stonework should be neat and approximately 1/2 to 3/4 inch wide. The color of the mortar used in the joints should blend with the natural color of the stone. In well-constructed stone masonry, the mortar is not conspicuous. In any event, the mortar should not be colored unless it is necessary to avoid unusually light color which contrasts unnecessarily with the color of the stonework. These joints should be raked fairly deep in order to eliminate so far as possible the effect of too much mortar, and to produce the effect of a natural dry stone wall.

CHIMNEYS

The chimney does not add to the attractiveness of any fireplace or camp stove. In fact, it is a rather unattractive feature which increases the massiveness, and for this reason it should be avoided whenever practical. A low chimney is sometimes not entirely effective, and, on the other hand, if sufficiently high to function satisfactorily the chimney may dominate the unit. The chimney, when used, may range from the simple funnel (pl. XXVI, figs. 9, 10, and 11) on the "ice box" and "oil drum" types of camp stoves to a definite masonry construction, as shown in plates XI and XII. It is confined usually to the camp stove. A low chimney may sometimes be constructed on a fireplace of the types shown in plates X and XI. This feature is most essential where the fire hazard is very great.

The height of the chimney should be kept to a minimum and may vary from 2 feet above ground, as shown in plate X, to 6 or 7 feet, as shown in plate XIII.

When the fire hazard is much above normal, the chimney should be provided with a damper control, and sometimes with a spark arrester (pl. XXII, fig. 3, and pl. XIII, fig. 3).

If the spark arrester is not used, there is great danger that the live sparks may be carried into highly inflammable timber. The spark arrester is a small mesh of woven wire screen in a frame, held in place at the top of the flue by means of prongs or clamps. It should be installed in such a way that its condition may be easily inspected and its replacement made simple.

The throat of the fireplace is that portion leading from the firebox to the chimney flue. In the regular indoor fireplace (pl. XXIII) the opening of the throat is about equal to the area of the flue and is the full width of the fireplace. In the camp stove fireplace (pl. XII), here discussed, the full width may not always be obtainable, but the proper area should be maintained, and so far as possible the width of the throat should be greater than its height (pl. XIII, fig. 3).

The chimney flue should in every instance be lined with a fire-clay brick or with some other regular lining. The height of the chimney, the size of the firebox, and the ashpit, as well as exposure, and type of vegetation surrounding the camp unit are important factors in the control of the draft. In general the area of the horizontal section of a round or a square flue from a single firebox should be not less than one-tenth of the transverse vertical section of the combined firebox and ashpit. An arbitrary minimum area for the flue might be 4 inches square. A rectangular flue should somewhat exceed the minimum area above stated. In camp stoves with open fronts on the firebox, the flue area should be further increased as indicated by drawings. A flue which is too large in relation to the firebox, tends to create a sluggish fire. In determining the size of flue for camp stoves other than for specific ones illustrated in this bulletin, use these illustrations as a guide.

In the multiple-unit type of camp stove, with a single square flue, properly lined, division by galvanized metal partitions into the proper number of smaller flues of proper sizes and each serving its own firebox, is essential (pl. XIII, fig. 4). This arrangement will prevent cold air from being drawn in from any unused firebox, thereby lessening the draft from the burning fire. The metal partitions will ultimately rust out and must be replaced. The installation of any damper in the chimney should be in accordance with drawings shown in plate XXII, figure 3.