between the model and case is full, by the glue coming out of it. The plaster case is next put into the position indicated by the line on the board, and fastened in this position by straps passing over it.

The glue should be of a good quality of white glue; it is heated in a double boiler until it is thin enough to pour. The space between the plaster case and the model is filled with the glue by slowly pouring it into the hole provided until it runs out of the air vent. It is then allowed to stand about 12 hours to congeal. The plaster case is removed, and the glue mould is taken from the model by springing its ends and sides slightly so as to allow the undercuts to slip out without injuring the model or the mould. The mould is kept in the plaster case so as to preserve its shape.

Before using the glue mould, its surface must be treated so as to make it waterproof; this is accomplished by washing it with a saturated solution of alum. Two or three coats are necessary, and each coat must be dry before the next is applied. In lieu of the foregoing, the surface can be varnished and oiled.

Sand Moulds.-Sand moulds are probably the cheapest moulds in which concrete can be cast, and at the same time they offer some advantages over all other methods of moulding. In a sand mould, it is of no account how great the undercut or how small the orifice through which the core has to be removed, for the sand after it has dried out can be crumpled into little grains and poured out of an orifice or scraped out of an undercut with great ease and without possibly injuring the ornament.

The process of making artificial stone by casting in moistened sand is described by W. P. Butler, the inventor, as follows:

"Opening Casting.-The first step in the process is to make a wooden pattern of the stone to be made. This pattern or model is made of the exact size of the stone desired, and it may be made in one or in several pieces. The size and style of the block usually determine the method to use in the casting of it. "The most common method of casting is that floor, or 'open-casting,' as it is commonly called. stones as well as small ones are cast in this way. embedded solidly upon the compound (which for call the sand), which is then packed solidly around it and built up until it is fully embedded in the same manner that a pattern is set

of casting on the Nearly all large The pattern is brevity we will

in the sand in a foundry. To remove the pattern from the sand it should be lightly tapped, so as to loosen it without noticeably enlarging the mould, from which it should then be withdrawn with the greatest care so as not to break down the edges.

"If, on examination, the surfaces of the mould are not perfectly smooth, or if any edge is broken down, or if any detail is imperfect or damaged, it may be 'touched up' or repaired with the moulder's tools which it is necessary to have.

"One perfect mould having been made, as many others as are desired can be made in like manner from the same pattern. A competent moulder can make from five to fifty moulds in a day, according to the difficulty or size of each. If the pattern has no projecting parts which would prevent its being withdrawn from the sand, it may best be made in one piece, but if there are projecting details or undercuts on the pattern, then it must be made in two or more pieces so as to make it possible to withdraw it from the sand without breaking down the mould This necessitates not only good workmanship on the part of the pattern-maker, but a thorough knowledge on his part of the necessities of the moulding process.

"The removal from the sand of a pattern of two or more pieces is done in the same manner as though there was but one piece, but it requires more time and care.

Compartment Casting.-If the block to be cast is for a cornice, belt-course, water-table, or any similar purpose where there is an ornamental or moulded face, with the other sides plain, a better and more rapid method of casting is to fasten two planks on edge, and parallel with each other, with partitions, fashioned between the planks at proper distances, forming a series of compartments in each of which is to be cast a stone. The length of the pattern or distance between the planks is made to equal the length of the block.

"The pattern in this case need be only the face of the block which is adjusted within the compartment at such a distance from the partition back of it as to give the proper width to the block. Then in the space in front of the pattern, solidly tamp the sand.

"Next loosen the pattern and draw it away from the sand, which retains the design of the face. This process is repeated in the

several compartments, and the moulds are then filled. By this method a minimum of time is required and blocks are formed much more rapidly than when moulded in a bed of material on the floor.

"Casting in Open-end Flasks.-This method will prove to be the best in many cases, especially where it is desired to pack the moulding compound vertically on the face of the pattern. In this process a box or collapsible 'flask' is open at the top and bottom. Within the flask and at the proper distance from the bottom is fastened the pattern or face-plate.

"Over and upon the top of the pattern tamp the sand and then fasten over this the cover to hold the sand in position while the flask is being turned over. Next loosen and remove the pattern, leaving the mould ready for the cast, wherein the face of the block alone is in the sand. When the cement is hardened the flask is

loosened and removed.

'Casting in Closed Flask.-Many pieces, such as balusters, balls, or similar turned forms, or forms which are symmetrical on all sides, must be cast in closed boxes or flasks.

"The pattern of the baluster is, in the case shown, made in two pieces which are embedded in the lower and upper halves of the flask. The patterns are then withdrawn and the two halves of the flask are carefully locked together. The cast is then made by pouring the liquid cement through the opening in the end of the flask. A great variety of the finest ornamental work is cast in this

manner.

"In all cases the cement and powdered stone, in the proportions of one of cement to three of stone dust, are mixed with water until of the consistency of thick gravy, and then carefully poured into the mould, using a pouring board or pipe to guide the stream and prevent its tearing up the sand. The mass is then allowed to set and harden for about a week before it is removed from the mould. This protection of the cement in the moistened mould prevents the cracking or checking of the surface. When the stone is fully dried out, the surface is brushed off with a wire brush to remove the surplus sand, and, if a tooled appearance is desired, the surface can be gone over with tools and then the block cannot be distinguished from one carved from the natural stone."

CHAPTER XV

CONCRETE PIPES, FENCE POSTS, ETC.*

Advantages of Concrete Pipes.-Moulds, Machines, and Manufacture of Reinforced Concrete Pipes.-Concrete Tile, Data, and Costs.-Advantages of Concrete Fence Posts.-Moulds, Machines, and Manufacture.-Reinforcement for Fence Posts. -Fastening Fence to Posts.-Quantity of Materials for Fence Posts.

CONCRETE PIPES*

A LARGE amount of concrete pipe is now being manufactured and used in this country. They possess many advantages over and are far superior to any other kind of pipe for many purposes.

Advantages of Concrete Pipe.-Concrete pipe can be manufactured practically anywhere. But little equipment is required and this can readily be obtained. Of the material necessary for manufacture, the sand and stone can always be found locally. The cement may have to be shipped some distance, but the cement constitutes but a small portion of the bulk. Thus, easily obtained materials, low freight charges, and low cost of equipment all make for a low-priced pipe. It costs less to make concrete pipe than to make clay pipe, and a better, truer, and stronger pipe is the result.

Properly made concrete pipe does not, under usual conditions, deteriorate with age, but instead grows stronger. The life of the pipe is therefore indefinite. This can be said of no other form of pipe. If made impervious it is immune from injury by acids, oils, alkali, and other disintegrating influences as explained in a previous chapter.

Concrete pipe, if properly made, is perfectly shaped and is truc at both ends. This uniformity greatly simplifies the laying of the pipe, as because of it all members will fit together easily and accurately.

* The best treatise on cement pipe will be found in “Cement Pipe and Tile,” by E. S. Hanson, editor of Cement Era, published by Cement Era Publishing Co., Chicago,

Ill.

Enlarged bells are not necessary for the proper jointing of concrete pipes. The pipe therefore may be of uniform diameter throughout, which greatly facilitates bedding and aligning.

Concrete pipe is not limited to the circle in shape, but may be varied to suit the conditions. Where the flow is variable the egg shape may be desired, and again where a greater area of bed is necessary a pipe with a flattened invert may be decided upon. Such shaped pipes may be as readily made in concrete as the more generally used circular ones.

Concrete pipe may be made of any strength desired by introducing suitable reinforcement. It may, therefore, be used for pipes under pressure.

Manufactured vs. Cast-in-Place Pipe.-When compared with a concrete pipe cast in place, the following advantages are claimed for a concrete pipe, made in short lengths in some convenient place, and then laid.

The pipe may be readily inspected both during and after manufacture.

Reinforcing metal may be accurately placed and kept in place until the concrete has been poured.

The forms may be used over and over again, thereby decreasing the cost of the pipe.

Being laid in short lengths, each length may be allowed to settle firmly on its bed before closing the joints. In large pipes the back fill may even be placed before cementing the joints. This minimizes the danger of the pipe straining or cracking due to unequal settlement. Also, under these conditions, when once closed there should be little or no tendency for the joints to reopen.

The disadvantage of a pipe laid in short sections is the number of joints. These joints are of necessity the weakest part of the pipe, and are therefore the controlling element. This inherent weakness is overcome to a certain extent by various special methods, as the use of metal ties between sections, or by lapping the reinforcement of one section over that of the next.

Moulds, Machines, and Manufacture -Various kinds of moulds and machines for the manufacture of concrete pipe have been designed and patented.

The simplest of these consists of an iron pallet, an outer hinged