Farm Building Construction

New Zealand Journal of Agriculture, Volume 95, Issue 3, 16 September 1957, Page 251

Farm Building Construction

By

H. W. T. EGGERS,

Engineer, Department of Agriculture, Wellington

THE preceding five articles in this series described foundations, framing, roofing ■ materials, sheathing, flooring, joinery, and internal finish. This article, which concludes the series, deals with new methods of building which though unconventional can help to reduce costs.

TIMBER has come to be accepted as the most versatile material for small buildings, probably because of the past abundance of suitable types. Though its versatility ■■ is not disputed, its suitability as a building material cannot be classed with that of other materials. Timber by its nature is subject to decay and the ravages of insects and fungus and has the disadvantage of non-permanence even with maintenance. Alternative materials such as metal and cement have the advantage of permanence without maintenance if they are correctly used. For example, galvanised corrugated iron has a limited life even with maintenance by painting. .The same material, however, factory treated with a bitumen asbestos compound will give what can be considered permanent service. Even materials which can be . considered : permanent are subject to deterioration, but if they are correctly treated and applied, deterioration can be prevented, thereby making them as. permanent as is < required. Buildings, which represent a capital outlay and an asset, should be constructed (unless designed as temporary) with materials which will give the greatest permanence with least maintenance, as once they are erected these materials will give years of useful, cost-free service. The alternatives to timber, whether brick, stone, concrete, or metal, all

give a satisfactory degree of permanence. Construction Methods At present what is known as frame building construction. is the universal method of constructing buildings with materials other than brick, stone, concrete, or stabilised earth. With' time this method has developed a definite pattern and is the method that has been described in this series. It can be described as providing a framework to support a weatherproof sheathing consisting of roof, walls, doors, and windows, the framework plus the sheathing constituting the building. Frames for buildings of this type in the past have been constructed almost universally from timber,, with the use in larger structures of perhaps a small quantity of steel for ties. With the enormous demands made on timber suitable for framing supplies of the . accepted types are dwindling rapidly and attention has been given to the use of other materials. ■ As. the technique of usage of any material must be decided . by the physical characteristics of the material, the use of materials such as steel, prestressed concrete, foamed or lightweight concrete, etc., in building construction must involve new techniques and different construction methods.

As the sheathing materials used in timber frame construction may be termed “unit” materials, in which the fabric is built up from sheets or tiles or other small units easily handled, so other materials which in themselves may be applied as a complete fabric can also take the form of unit materials. An example of this is concrete, which can be used with reinforcing for the building of a continuous structure or in the form of concrete blocks, which are a unit material. . ■ As some unit materials like bricks or blocks cannot be effectively bonded together to produce in themselves a rigid structure, some method of reinforcing must be applied to produce the required rigidity. Unit . materials are particularly suited to frame construction because they need not be depended on for structural rigidity, rigidity being supplied by the frame to which they are attached. As the uses to which materials alternative to timber can be put in building construction depend on their physical characteristics, the sphere of utility or method of utilisation is varied by the range of those characteristics. Some alternative unit materials may not have the crushing strength or the rigidity to make them suitable structural units, and therefore loadbearing characteristics and rigidity must be supplied by other . means, which may be a frame, reinforcing, or a combination of both. An example of this is pumice or breeze concrete blocks, which have not the necessary crushing strength*to make them suitable for support walls but which can still be used as a fabric for such 1 walls by the provision of reinforced-concrete piers and tie bands to provide the required load-carrying capacity and rigidity. . Between the two limits of true frame and continuous construction

there is a wide field of methods of construction all of which are suited to the particular materials being used. These methods may embody some principles of each type of construction in varying proportions according to requirements as shown .in the description of light-weight concrete construction later in this article. Steel Framing Materials The quest for alternative materials to timber has produced systems of building frame construction using steel either in industrial sections or as tubes. Industrial sections are fabricated into a type of truss which can be used as a universal member for either roof or walls. Steel tubes are used for columns, trusses, and purlins, being joined with special fittings in which grub screws are used for fastening. Firms offering steel-frame buildings can provide for hay barns,, implement sheds, grain stores, manure stores, garage workshops, and livestock shelters. The buildings can be supplied as a kit set, which includes all-steel members, timber members where used, all external sheathing, windows and doors, and all nails and bolts necessary for the farmer to construct the building himself. Alternatively steel work only can be supplied all ready for bolting together, the purchaser providing all woodwork and sheathing. Alternatively steel work for roof only can be supplied, the purchaser providing the remainder of the structure, or the structure can be erected by the suppliers complete if the farmer so desires. All firms offer their structures sectionalised so that initial structures can be extended by the addition of more bays. One firm offers a standard framework which . allows for future partial or complete covering in and fitting of doors, which enables the user to salvage or purchase his coverings piecemeal and fit as he so desires, thus reducing the initial outlay required for a partial or totally closed-in building. As all-steel-frame buildings are sectionalised, sizes must conform to a pattern decided by the manufacturers. One firm can supply a -wide building .with a 12ft. stud in multiples in length of 10ft. from 20ft. to 60ft. Another "can supply implement sheds 15ft., 16ft. 6in., 18ft. 4in., 20ft., 21ft. 10in., 23ft., 25ft., 27ft., and 30ft. long by .15ft. wide, all'sizes having an Bft., 9ft.;>loft., lift., or 12ft. stud. Hay barns are available 30ft., 45ft., and 60ft. long by 20ft. wide; 45ft., 60ft., and 75ft. long by 25ft. wide; 45ft., 60ft., and 75ft. long by 30ft. wide, all sizes having 12ft., 14ft., or 16ft. stud height. These hay barns can accommodate 900 to 4500 bales of hay according to their size.

The cost of these buildings naturally varies with the amount of materials and labour provided by the suppliers; for example, an implement shed open in the front, 45ft. by 20ft. with a 10ft. stud, is available as follows:

£ s. d. Basic price—1 bay of. 15ft. 105 0 0 + 2 bays of 15ft. at £49 98 0 0 203 0 0 Timber if supplied . . . . 42 10 0 Corrugated iron if supplied 126 0 0 Spouting, ridging, and down pipe .. .. .. .. 11 12 0 Total 383 2 0

or approximately Bs. 6d. per sq. ft. of floor area. Similarly a 40ft. by 20ft. shed with 12ft. stud can be obtained complete with sliding doors for £640, or the steel framework only can be purchased for £316 12s. This shed complete is approximately 16s. per square foot. For buildings with steel as a substitute for timber as a framing material the choice and cost will depend entirely on individual requirements and the amount of material bought as against materials salvaged. Steel trusses are also available for bridge construction for spans from Bft. to 20ft. with a width of 10ft. and track width of Bft. 6in. The decking for these bridges (which is not supplied) is 9in. by 4in. hardwood at lin. spacing. These bridges will carry a load of 12 tons and cost approximately £6 13s. 6d. per foot. Tubular steel with the fittings mentioned previously for junctions can be used for fences, gates, holding pens, bull yokes, or for any other application where a strong permanent structure is required. Wherever steel buildings are required choice should be made only after consideration of all equipment available, as some types may be more suited to individual requirements and purse than others. Pre-stressed Concrete Pre-stressed concrete is a new material for building construction and can replace timber for any beam members such as floor joists. It is essentially a factory product and is made by reinforcing uniform concrete with steel wires tensioned with special equipment. This places the concrete under compression and as its compressive strength is its greatest characteristic, less mass of concrete can be used to produce beams of equivalent strength to similar beams reinforced by normal methods. The total weight of reinforcing is also reduced. Pre-stressed concrete floor joists can be used in three ways to give composite floor construction.

Pre-stressed joists and blocks: Light pre-stressed joists with infilling blocks of pre-cast hollow concrete or terracotta are bonded and covered with an infill of screed concrete. The joists require projecting stirrups to bond the infill and screed concrete to produce T beam action. No shuttering is required for this floor. Pre-stressed joists and in situ slab: Pre-stressed joists are placed at calculated spacing and a reinforced slab cast over them. The slab shuttering is supported by timber spreaders placed between the joists. Pre-stressed joists and slabs: Prestressed joists are placed and pre-cast (light-weight) slabs placed over them. The whole is tied together as a monolithic floor by stirrups or joists and a screed concrete covering. No shuttering is required. Light-weight Concrete Concrete used as a unit material for building construction either as blocks or slabs has a disadvantage in its weight. Solid unit members cannot be made in convenient sizes because of weight, and attention has therefore been given to producing a lighter material without sacrificing any necessary qualities of strength. Units such as blocks are produced with cavities, and natural, light-weight aggregates are used for making slabs and blocks. Concrete is produced less dense in structure and containing air cells by eliminating the fine aggregate (no fines concrete), by air entraining, or by foaming. Any alteration in these ways to the structure of normal concrete naturally alters its physical characteristics. The inclusion of air in the structure while reducing the crushing strength increases the thermal insulating properties of the material. Average normal concrete has a density of approximately 1501 b. per cub. ft. If this density is reduced to 701 b. by air entrainment, the heatinsulating properties are increased nearly four times. This treatment of concrete, though partially sacrificing some properties, is also providing other properties which are valuable for building construction, and it is on the degree in which some properties can be sacrificed to gain the advantage of others that the successful application of light-weight concrete as a unit material has up to the present depended. The theory of foaming or air entraining concrete is to permeate a dense material with minute bubbles of gas or air not only to reduce weight but to give better insulation properties. These processes must be controlled and are therefore particularly suited to factory production of unit materials.

Apart from the use of natural lightweight aggregates the first attempts to produce light-weight concrete artificially were directed along these lines. With the introduction of artificial light-weight aggregates such as perlite and vermiculite the theory has changed to virtually foaming the aggregate instead of the concrete. This change of technique produces an aggregate suitable for the making of light-weight concrete by normal methods as used by the farmer or anyone making concrete by semi-con-trolled methods. With air-entrained or foamed concrete a balance must be struck between required strength and insulation properties,. the . density and relative strength being varied by the degree of foaming or air entrainment given. Under these conditions water, foaming additive, cement, and sand ratios and mixing times are critical to produce a concrete of any particular density and must be closely controlled for each batch or mix to ensure no variation between mixes. Light-weight aggregates, being foamed in themselves, can be produced in densities regulated by the gases given off by chemical reaction during the calcining process. This differs with the raw materials used. Some minerals when treated become virtually a mass of tiny bubbles giving an extremely light aggregate; others have varying degrees of air impregnation which will produce concrete of corresponding densities. With the very light, highly bubbled aggregates concrete density can be controlled by mix proportions; for example, with one particular aggregate a mix of 1 part of aggregate with 1 part of cement produces concrete of a density of 841 b. per cub. ft., whereas a mix of 8 parts of aggregate with 1 part of cement produces concrete of 211 b. density. The density of concrete produced with aggregates having more of an air-entrained nature than bubble formation, though depending on the density of. the particular aggregate used, can be varied to some extent by grading the aggregate. Generally the larger is the aggregate the less dense the resultant concrete. Foamed Concrete As foamed concrete lends itself to factory production, unit building materials can be factory produced. If these are designed for simplicity of erection, they give a satisfactory building from permanent materials. A method of using foamed concrete units for building construction is shown in the illustrations in this article of -an implement and storage shed and a garage. The construction to top plate level is carried out in piers and panels. The strength and rigidity sacrificed in producing a light-weight panel are regained in the piers and reinforcedconcrete top band. Both piers and panels are pre-cast in foamed concrete

of. a density of 901 b. per cub. ft. Grooves are provided in the piers into which the stepped edge panels fit. Both piers and panels are reinforced, the pier reinforcing being bonded into the foundation "and top band reinforcing, thus producing a rigid structure. The foundation, piers, and top band provide the rigidity and support for the panels. Being factory produced this unit building material requires very little labour for erection- and can be produced quite cheaply. For example, the implement shed shown was erected complete with roof and guttering by 4 men in 8 days, 230 miles from the factory, at a total cost of 10s. per square foot, which compares more than favourably with the Bs. 6d. per square foot for the bare implement shed with steel frame mentioned earlier and which had a non-perman-ent sheathing in place of . this permanent material. Plastic Sealing Compounds The conventional practice of sealing joints in sheathing members such as glass to window frames, butts in weather boarding, etc., against the elements is to use a putty or bituminous preparation which hardens with time. Ordinary putty composed of whiting and oil becomes rock hard in time and quickly cracks with repeated expansion and contraction. . Even bitumen-based preparations harden out to become unserviceable. Socalled non-hardening putties also harden in time, but take considerably longer than ordinary putty. As nearly all structural joints are subject to working through several causes, any putty which sets hard is not a suitable medium with which to seal such joints. With the advent of

plastics putties have been produced which will not harden with age. These putties skin on the outside and can be painted over, but retain a permanently soft core which . gives them flexibility. For this reason they are not suitable for sealing in places where the putty cannot be given some volume; for example, if used for stopping gaps or cracks up to Jin. wide, they will skin right through and become useless as a sealer. Where, however, they can be used in grooves say Jin. wide or as a fillet for sealing in corners such as glass in window frames, the skinning effect cannot penetrate right through and the soft, flexible core is retained. Plastic sealers of this nature which are specially designed to seal. moving joints permanently and satisfactorily are available in different types each particularly suited to certain applications. There are types for sealing cracks in concrete water tanks and joints in concrete slabs; there is a type which can be readily moulded into special jointing shapes for pipe flanges and other joints, and there is a type which can be used for all sealing purposes where ordinary putty can be used, provided it is given volume. This latter type is marketed in a form suitable for application by hand gun, which greatly simplifies its application, as fillets can be run or grooves sealed with an even disposition of material by simply operating the gun. Possession and use of one of these sealing guns constantly bring to light new uses for this material such as the sealing of joints in’ replacement guttering, which is' normally a difficult job, as the guttering is under the overhang of the roofing. These guns are not expensive and are an excellent means of applying the

sealing compound, being very easily handled. The sealer is available . in cellulose-wrapped cartridges which are placed in the gun for use. After use the cellulose wrapper is extracted from the gun, in which another cartridge can be placed. One big advantage in using a gun for the application of this sealing compound is that there is no loss of compound with intermittent use. The gun can be put away after use for an indefinite period with no deterioration of any compound left in it. When it is taken out and used again a small quantity of compound is wiped away from the nozzle and the gun is ready for immediate use. Waterproofing Compounds Building materials such as brick, stone, or concrete, being of granular construction, have hygroscopic characteristics and can absorb and retain moisture. It is this fact, together with atmospheric conditions and the presence of micro-organisms, which produces the ageing of construction materials. The atmosphere with its variation of temperature and pressure and variable pollutions according to geographical localities can lead to sulphurations (in towns) or chlorinations (near the sea) and erosion by wind and rain. Microorganisms by transforming insoluble

salts into soluble ones permit moisture to draw these salts to the exterior surfaces and their crystallisation leads to the formation of blooms, with consequent disintegration of the granular structure. If the entry of moisture to these materials by capillary action could be prevented, erosion and destruction by ageing would be considerably reduced. This can be accomplished by two methods. The first consists of disposing a continuous coat on the surface of the material to produce a mechanical dam. The efficiency of this method is subject to its resistance against wear and the permanence of the coating material used. The second method consists of treating the surface of the material to suppress the mutually attractive actions of the material and water. The granular structure of these materials entrains a volume of air which is subject to expansion and contraction with changes of temperature, causing respiration of the material. The sealing of the surface with a mechanical dam also seals in the entrained air and prevents respiration. This can cause a pressure differential between the entrained air and the outside atmosphere,, resulting in the lifting of the surface membrane. Treatment of the surface of the material to suppress capillary action

of moisture does not seal the surface in such a manner as to prevent respiration. The material can still breathe and retain an internal and external equilibrium. Synthetic resins are . available in solution which when applied to these materials by brush or spray coat the granular structure with a thin waterproofing coating which makes the grains shed water but does not make the surface impermeable. This coating is carried to a depth of a few millimetres, depending on the density of the material. It does not change the colour of the surface, is invisible to the naked eye, and can be detected only by the action of water on the treated surfaces. The solutions are procurable in two types, one with a spirit base which is suitable for all normal dense materials and one with a water base which is suitable for less dense materials such as concrete made from light-weight aggregates. If a spirit-base solution were used on materials with relatively high absorbent properties, deep penetration would occur, with consequent dispersal of the water-repellent film. For this reason a water-based solution should be used on absorbent surfaces.