US2531990A - Method of molding concrete building units - Google Patents

Description

Nov. 28, 1950 E. J. RAPPQLl METHOD OF MOLDING CONCRETE BUILDING UNITS Filed Nov. 18, 1947 RH. u 0 +P NP A VR J 10 Patented Nov. 28, 1950 UNITED STATES PATENT OFFICE METHOD OF MOLDING CONCRETE BUILDING UNITS Edmund J. Rappoli, Medford, Mass.

Application November 18, 1947, Serial No. 786,705

1 Claim. 1

My invention relates to a method of making concrete building units, and more particularly large heavy concrete slabs or sections of buildings with smooth, finished surfaces which do not require plastering or surfacing.

The present high cost of building construction is well known, and has prevailed for several years, notwithstanding eiforts by architects and engineers to simplify construction and to make substitutions, and notwithstanding their tolerating lower quality material and workmanship.

It has long been desirable to use concrete in-- stead of masonry wherever possible, as the cost of masonry has been particularly high. Also, building codes favor the use of concrete for its superiority in strength, durability, versatility, reinforceability and fireproof qualities over brick, tile, or ordinary building blocks. The Boston building code, which is typical of others, allows compression working stresses of 500 to 1125 lbs. per square inch for concrete; 100 to 300 lbs. per square inch for grade A brick; 75 to 225 lbs. for grade B brick; 100 to 150 lbs. for concrete blocks; and 80 to 100 lbs. for structural clay tile. Yet notwithstanding the obvious advantages and the long standing demand, attempts to use conrete instead of brick work or other masonry have not been widely successful. Small concrete houses have been precast, or formed almost entirely by special machines, but the size of most buildings, and especially public buildings, precludes such methods on any considerable scale. It has been found that expensive pouring and forming methods and machines ofiset the advantages of using concrete. Furthermore, concrete walls require plastering on both sides for interior walls, and furring, lath and plaster against the inner side of exterior walls in order to provide a suitable finish. Thus, while concrete walls are stronger and originally less expensive than masonry, the difficulty of making them and the cost of finishing them has prevented their widespread acceptance.

The primary object of my invention is to make it possible to use concrete successfully without the many difficulties heretofore attendant on its use in buildings. Other objects are to make building sections of smooth, clean-surfaced concrete which does not require finishing, and to provide a better and stronger construction material.

I have found that wall sections or slabs can be made which weigh several tons, sometimes as much as fifteen tons, and having smooth, finished surfaces which eliminate the need for plastering, furring, lathing, etc. In carrying out the process of my invention, I precast the concrete in horizontal molds. A mold or form base is laid, and its walls are built to the height required for the thickness desired for a building section. The form is filled with concrete which is vibrated, levelled and trowelled smooth. Ehe material is then allowed to dry, usually until white. After the concrete has set for about a day, the top surface is coated with lacquer. In less than one hour the lacquer dries to a tough, hard film which is firmly adherent to the concrete to which the liquid is applied, is strongly cohesive, and has a very smooth hard top surface which will bear another layer of concrete. The edge form is then built up, and a second layer of concrete is poured. This layer, though wet and heavy, will not injure, displace, dent or adhere to the hard film beneath. When the second layer is likewise partly dried, another film of lacquer is formed on it. After drying for about four days, concrete sections are hard enough to handle and hoist into place. They could not at this stage withstand the strain of separation without cracking or blistering, however, except for the very hard and smooth film which is permanently adherent to the lower and yet non-adherent 'to the upper slab. The separated slabs, because of the nature of the film, are smooth on both sides, and one side has a permanently adhering finish.

In order to save space, time and materials, the edge forms or molds will usually be built up until they contain six or more castings depending on the number of slabs needed and their thickness. After the last formed slab has become hard enough to use, the slabs are stripped from the pile or stack by cranes and hoisted into place in the building being erected. Each slab will usual- 1y be a complete wall or a large section of a wall, and one dimension will usually be equal to the wall height between two floors. Such building sections will often be as much as twelve to fifteen feet wide and twenty or twenty-two feet long and if intended for a bearing partition and about eight inches thick, they will weigh as much as fifteen tons.

The invention can be better understood from the following description in conjunction with the accompanying drawing, in which:

Fig. l is a view in elevation showing a form or mold partly cut away and containing several precast concrete slabs, and

Fig. 2 is an isometric view of a precast concrete section.

In Fig. 1, the form M is provided with a concrete floor l and wooden side pieces 2. The base is coated with lacquer, and the lacquer allowed to dry to a hard film. A layer of concrete 3 is poured, levelled and trowelled, and allowed to dry until hard enough to support the weight of a superimposed layer. This will usually require about one day. The first layer 3 is then coated with lacquer. The liquid lacquer does not penetrate very far, but it is strongly adherent to the surface of the concrete. It dries ver quickly, usually in less than one hour, and forms a smooth, level, hard film 4. This ensures that a superimposed layer of concrete will not displace it, leaving thick and thin places, or cause it to be e};- truded or pressed out. When it is sufficiently hard, so that it will not stock to a superimposed casting, the second layer of concrete 5 is added, and allowed to set for a day, and then its top surface is coated with lacquer. Usually the procrise is repeated until the form or mold is built as high as is feasible under the circumstances. It is not unusual to have as many as six' or more layers, and as many as twenty-five sections can sometimes be molded in each stack or pile.

In carrying out the process, varnish and shellac may also be used, though they are not quite as good as lacquer. Experiments have shown that other materials", which do not form hard films which are strongly adherent to one surface, but not the other, cannot be employed. Paint should not be used, as it will peel. Oils should not be used, as the will damage and weaken the wet under surface of the succeeding layers of a stack,

and will also form honeycomb pockets. They would also form areas of adhesion between the two surfaces which, on separation of the layer, would cause a piece of one of them to be torn out and stick strongly to the other, thus spoiling" both layers or slabs. Powdered and granular material must not be used as they would r'oughen the surfaces, and sheet material like waxed paper, for example, would cause wrinkled and rippled surfaces. A very quick-drying liquid is required. It should preferably be viscous. It must adhere firmly to the top of the lower slab, and form a dense, moisture-impervious coat, which will neither stick to nor penetrate the lower surface of the superimposed slab. The coat must be strongly cohesive, so that it will not be displaced or pitted by the upper sections. It must be capable of standing the strain of vibrating or compacting the upper section, a practice used to form hard dense surfaces. It performs three services: it serves as a separator for the sections of the stack; it serves to form smooth surfaces on both sides of the slabs, and it forms a finish coat on one side of the slabs. Even in cases where it might be supposed that an adherent coating might be dispensed with, lacquer or the like still required for the smooth surface, without which the building section could not economieally be used. V

The advantages to be gainedby employing the invention will be obvious. When concrete is molded in vertical forms, the high head or hydrostatic pressure on the lower portion tends to spread the molds or compress the material of the molds, so that in no such molding of any size is the molded section absolutely uniform. Furthermore, the wall surfaces are not smooth, as there are ridges or gaps between the adjoining sections of the lining or facing Of the forms. The surfaces require plastering or furring. If a concrete wall must be furred, plastered or veneered, then the expense is so great that the advantage over the use of masonry is lost. But when the precast sections of my invention are used, the walls are uniform and smooth on both sides. Since furring, lathing, plastering, etc., are eliminated, precast concrete walls are less expensive than ordinary brick, tile, or building block walls. The invention makes it possible to use stack molding, which conserves space and materials, and often saves time. There are no pockets formed between the concrete layers, and no vacuumatic adhesion. The forms are easy to construct, and do not require skilled carpentry. It will be recognized by those skilled in the art that the precast building sections of the invention are not an inferior substitute for ordinary concrete or masonry walls, but are in fact better than masonry walls or concrete walls which are molded in place in the building. When the sections are secured in place, it is only necessar to paint them. A series of such sections, when only coated with paint, cannot be distinguished from a well-plastered wall. The precast walls save considerable space as they require only a fraction of the thickness of the customary masonry and plaster wall combination, and result in stronger and better buildings.

I claim:

The method of making concrete building units having smooth surfaces on both sides which includes the steps of making a horizontal form, filling the form with concrete, levelling and trowelling the concrete, allowing the concrete to harden sufliciently to bear the weight of a secend section, coating the top of the concrete with lacquer, allowing the lacquer to dry to a hard,

" cohesive film adherent to the top surface of the concrete and non-adherent to the adjacent lower surface of a said second section thereof, building up the sides of the form sufficiently to hold a second section of concrete, filling the upper portion of the form with concrete, allowing the second section of concrete to harden, repeating the steps of coating and molding until a stack is formed, and separating the sections of the stack.

EDMUND J. RAPPOLI.

REFERENQES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 753,491 Hoffman Mar. 1, 1904 1,600,514 Seailles Sept. 21, 1926 1,628,681 Newman May 17, 1927 1,657,566 Crozier Jan. 31, 1928 1,744,702 Leeder 1 Jan. 21, 1930 2,143,515 Hayden -11- Jan. 10, 193.9

Images