1855. 



NEW ENGLAND FARMER. 



527 



then, is to know what is the smallest amount of' sand, stone broken into small fragments, broken 

 cementing matter admissible in its preparation. | bricks, gravel, shells, and the like. The coarser in- 

 The cheapest, and only allowable combination, (5 //ie gredients arc added to the mortar of sand and 

 filling of the void spaces of the sand. To ascertain ceHie??<7Hg" matter, vnth a view of giving hardness 

 the void s|)aces, ^// a vessel of known capacity, and incorapressihility, and of lessening cost — and 

 with dry silicious sand, and after shaking it com- this cost is reduced to the utmost bv the use of 



pactly, add water until it ajjpears on the surface, the 

 quantity of water is the measure of void spaces of 

 the sand. The rate recommended by Lieut. Wright 

 for proportions, is, to twelve measures of coarse 

 dense sand, five of the cementing ingredients in 

 paste somewhat firmer than pro])erly tempered 

 mortar. To five measures of middling sand, two of 

 the cement ; to three measures of fne sand, one 

 measure of the cement. A cask of stone lime 

 weifjhinir 240 lbs., net, will pi-oduce 8 cubic feet of 



stiff" paste, and will admit of sixteen bushels damp >be the minimum of mortar, and would rarely pro 



loose sand ; and the lime paste should become cold 

 before the sand is added. 



From the extended quotations and remarks on 

 the adhesive mixture for gravel or concrete build- 

 ings, it is ap])arent that the true principles of mor- 

 tar-making should be api)lied to those, of all other 

 buildings. 



Bricks are porous, and the carbonic acid of the 

 atmosphere, small as it is, being only one part in 

 one hundred, will in time reach the mortar to a 

 considerable dej)th from the surface. The unavoid- 

 able interstices in the concrete, admit also the at- 

 mosphere, and besides, the walls may be ventilated 

 from bottom to top at intervals of a few feet by 

 moveable tubes, round or square, to draw up as 

 the Avork advances. The ventilators serve to harden 

 the mortar at these points, and rapidly strengthen 

 the wall. 



Of the buildings erected in this vicinity of con- 

 crete, the majority stand, and it is much to be 

 hoped they will stand to a remarkable old age. 

 Others have fallen, and of those fallen an examina- 

 tion shows that the stones and particles of gravel 

 were httle more than ivhitewashed, without an ap- 

 proximation of adhesive mixtures to bind the par- 

 ticles together. 



Of those concrete buildings which have flillen, one 

 at Lexington was built on a wet site. The base- 

 ment was some of the time under water, and upon 

 a foundation of lime concrete. The desigji was, one 

 story above the basement, and the thickness of the 

 wall one foot. But it was carried up two or three 

 stories. While the frost remained it stood, and 

 when it came out it fell. One at Lynn, 2t stories, was 

 placed on a stone foundation, supposed to Ije good ex- 

 cepting the lack of a thorough coating of hydraulic 

 cement above the underpinning, on which the con- 

 crete should be placed, to prevent the attraction of 

 dampness from the ground, — a precaution needful 

 to a brick or stone building as well as to one of 

 concrete. It was thought by the owner that the 

 foundation started, and with it the whole edifice 

 came to the ground, filling the air with a |>crfect 

 cloud of lime powder. It was built of gravel and 

 smooth cobble, without the coarser rubble stones, 

 and probaljl}- nearly destitute of such a ]ireparation 

 of mortar as is requisite to hold brick and stone and 

 gravel together. 



Lieut. Wright says "that the French beton and 

 English concrete are used for similar jjurposes. 

 Beton or concrete is nothing more than a mortar, 

 to which are added coarser materials than are found 

 in sand. The materials jirojier for use in the manu- 

 factui'e of concrete, are h}draulic lime or cement, 



fragments of various sizes, and sometimes by a cer- 

 toin proportion of gravel, in order to make the sum 

 of the voids as small as possible. Of the materials 

 employed at Fort Warren, brick fragments have 

 usually been preferred as affording the best results. 

 The proportion of cementing matter should always 

 be such as to form good mortar, with the sand alone ; 

 and the morbir, thus composed, must always be ad- 

 ded to the solid particles, in the least sufficient 

 quantity to fill up the voids. This, however, would 



duce a good result. An excess over this amount 

 has been always used in the com])osition of concrete 

 at the public works in Boston harbor. 



The concrete for the sea-wall at Lovell's Island 

 was prepared by mingling mortar of hydraulic 

 cement and sand, and a shingle or gravel of slaty 

 texture. This gravel consisted of all sizes, from the 

 bigness of a pea to stones of six inches in diameter, 

 so proportioned as to fill the void spaces. A batch 

 of mortar was composed as follows : 1 cask cement, 

 equal to 3| cubic feet stiff paste ; 10^ cubic feet damp 

 loose sand, equal to 8 cubic feet dense sand. One-half 

 of the sand was put into a box and spread out, then a 

 cask of cement, and over this was s])read the remain- 

 der of the sand. Water was then added, sufficient to 

 produce a somewhat pliant mixture, and then mixed 

 in the usual way. The result was 10:^ cubic feet 

 of quite stiff mortar. This batch was mixed with 



3 1 i cubic feet of gravel, the void spaces of which 

 were estimated at 20 to 25 per cent, of its volume. 

 The minimum of mort;ir would be between 7 and 8 

 cubic feet, but two more feet were allowed to com- 

 pensate for imperfection in the manipulation. The 

 concrete was i)repared by spreading out the gravel 

 on a platform, in a layer from 8 to 12 inches thick, 

 the smaller pebbles on the bottom and the larger 

 on the top, afterwards spreading the mortar over it 

 as uniformly as ])Ossible. The materials were then 

 mixed by four men, two with shovels and two with 

 hoes, the former facing each . other, and always 

 working from the outside of the hcaj) to the centre, 

 then stepping back and recommencing in the same 

 way, and thus continuing the ojieration until the 

 whole mass was turned. Then men with hoes work- 

 ed, each, in conjunction with a shoveller, and were 

 required to rub well into the mortar each shovel full, 

 as it was turned and sj)rcad, or rather scattered on 

 the platform by a jerking motion. The heap was 

 turned over a second time, in the same manner, but 

 in an opposite direction, and tlie ingredients were 

 thus thoroughly incorjjoratcd, the surface of eveiy 

 pebble being well covered with mortar. 



Two turnings usually sufficed to make the mix- 

 ture complete, and the resulting mass of concrete 

 (33 { cubic feet) was then ready for transjmrtation 

 to the foundation. The concrete was taken to the 

 foundation, levelled and rammed. The rammer 

 was a cylinder of wood 8 inches in diameter and 8 

 inches high, and its base was faced with sheet iron, 

 and furnislied with a handle 3 to 4 feet in length. 



There was ]irei)ared a quantity of mortar, with 8 

 cubic feet of stiff Hme paste, 1 Vi stiff' cement paste, 

 and 42 cul)ic feet of damji and loose sand, equal to 



32 culiic feet of close sand. The products amount- 



