Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/157

 Fes. 16, 1872. THE BUILDING NEWS. 141 cases hydraulic lime might be substituted. Should the place be very wet, keep out sand, and if cement be as it ought to be, energetic, it will set in a few hours. It is sometimes used half-watered above eground, but why, I never could learn. No doubt too much water is injurious in some cases, as whena vast body of concrete is used together, for the sur- plusage of water cannot well get out. However, the exact quantity here required is easily ascertain- able. The property of cement to swell greatly {is well known, so that great masses, half-watered, will need further hydration to perfect it. Now, will the masses not swell, and that irregularly, lifting irre- gularly what is on them, thus doinginjury? I giveno opinion. Of béton I shall not say much, except of prepar- ing the mortar, but first I shall note the following: The mortar ought to be so thin as to mix with the gravel, broken stones, or other materials, and to adhere to them. As to quantity of mortar, no rule can be given, as each different set of materials will require a different proportion. This is best settled by trial. The mortar must be carefully mixed in and wrought through the stones or whatever be used. It should be carefully laid in courses of no great thickness ; I think six inches or thereabouts is as much as can be thoroughly beat through ; certainly much more cannot, and it is best to be on the safe side. Each course or layer should be thoroughly rammed till the mortar squeezes out; but on no account must the ramming be continued till the mortar is set; and layer should follow layer quickly enough for the top always to adhere to the layer imme- diately below. Whoever may think that he can thoroughly beat through, say, a foot, Jet him try his hand on soft soil, and then cut through downwards and examine. Broken stones or brickbats are before gravel for béton, and I think for concrete too, but wherever used they must be rammed. With regard to mortar, it should be well wrought with spade, or other method to serve the same end—that is, to work the lime and sand thoroughly, consoli- date the mortar, and as a consequence, render it more tenacious. Raking mortar makes it light and porous, and works the grains of sand to lie in great confusion in the mortar. Nor will the rake com- pletely mix the lime and sand as it ought to do. The after-working with spade corrects this, at least in part. Any one who has not already done so, dry a piece of rake-finished mortar and a piece of thoroughly wrought mortar after a raking, break them and com- pare them under microscope, wher he will be sur- prised at the difference in texture, arrangement of sand, and distribution of lime which, if the micro- scope be good, he will see plainly more or less fully enveloping the sand grains. But I have said on this head all I mean to do, except to say that the examination of old béton walls would be more to the purpose than anything I can say, and that best always contain gravelly sand. Besides, I mean at some time to give my notes on the said old walls. As to the concrete blocks for backings, &c., I really have not much to say, except that the want of mixing has been the great fault throughout. The materials were never properly mixed, and, if mixed, thrown in so carelessly that the larger and smaller are completely separated, the larger being together nearly without cement. The mixing ought to be done exactly as I have stated for lime concrete, but with even more care, especially in putting into mould. Ram, but not when set, and fill as fast as possible, and if two mixing-boards be not enough, get more. The proportions may be taken roughly as follows:—6 of mixed gravel, 4 to 2 sand, and 1 cement, no single piece of gravel being larger than would turn in a 1tin. ring, and if pack- ing inside be partially resorted to even less. Packing, if well done, I should recommend, but in packing I should advise also to take heed of following :—Do not use the packing in large pieces, do not use small water-worn boulders, but anything else hard enough; never let two pieces of packing actually touch each other; bed well in concrete, and beat down while soft ; very little beating will do. Take care that packing is thoroughly imbedded in con- crete.’ These things minded, and not packed to heayily, the concrete will be as strong nearly as without packing, and much cheaper. Kezp packing from outside of block. As regards concrete blocks for river walls, I beg to note the following :—In those I have seen the old fault of mixing was invariable, causing them to be made good with cement patched on, and rendering them permeable by water, therefore destructible by frost and other causes, especially by boats, &c., grinding against them. The former can be easily remedied ; the grinding evil we shall consider next ana lastly. For concrete to face river or other similar walls I object to gravel being used in toto, and the same may be said of bearance blocks. The water-worn surfaces are too smooth to allow cement to adhere properly, thus causing the blocks to be weaker than they ought to be, and being of hard flint they do not wear as cement does; they, there- fore, soon get slightly prominent on outside, and in the end chucked out. To obviate these some material ought to be chosen that will just wear as the cement does, neither faster nor slower (for, like stone, the blocks will wear); at the same time it should have such grain and sur- face that the cement will adhere tenaciously. Hard burnt clay is the best I know of, for, when ecrystal- line, it answers the requirements given, and another —that is, it will not be affected by any agent likely to do so. The regular wearing I have seen tried, not in river walls, however, but yet where the cause for wearing was very great. Its power of resisting breakage as lintels is great, too, for IT have known a moderately hard stone break before concrete of the same dimensions, the same weights being put on till the stone broke, and then a little more added to break concrete. However, I do not put this as conclusive. Of mixing, &c., what applies to the former applies here every way, except that I would have the sand less and material rather smaller. In both cases the blocks should turn out of mould smooth as a casting. I may return to the subject.—I am, &c., C. A, WeDDLE. 37, Hyde-street, Winchester. UNPROFESSIONAL CONDUCT. Srr,—I can well understand the feelings which have induced ‘Occhifer” and ““W. Seckham Witherington” to address you (see pp. 100 and 122) for the purpose of exposing the unprofessional treatment of which they complain. I can also un- derstand that such exposures may prove of indirect benefit to the profession at large by preventing re- petitions of such treatment. May not, however, the remedy prove worse than the disease, for is not the honour of an honourable profession placed in jeopardy by having its dirty linen thus dragged for- ward and washed in public? The readers of the Burtprine News are no longer only architects and builders, and the world at large not being in the habit of discriminating very closely, will be apt to accredit to the many what are really only the imper- fections of a few. If the “Institute” is ever to become of practical benefit to the profession, let it step forward now and show it by appointing a committee before whom architects may lay the tale of their professional grievances. The utmost, probably, that such acom- mittee could do, would be to express an opinion, or perhaps utter a remonstrance, but surely this would have quite as deterrent an effect upon unprofessional practices as writing letters to the newspapers, be more likely to secure compensation to the injured party, and save, at any rate, the credit of an honour- able profession from the constant exposure of mal- practices on the part of a few of its less scrupulous members.—I am, &c., ScRUTATOR. FOUNDATIONS. Srr,—You have published several letters on build- ings founded on clay that have sunk and cracked ; would you allow me to call attention to a few omis- sions which, I think, require supplying before a correct answer can be given ? 1. In what part of the country are the cracked houses? (I suspect, bordering on the Fens.) 2. What sort of clay is it ? 3. What thickness is the clay bed? and 4, What is the underlying stratum ? I strongly suspect that the clay lies on a quick- sand, or some other loose substance, that holds and is capable of holding a large quantity of water, and I should not be surprised to learn that by a drain or drains the substratum has been tapped, and water drained and draining off, which would just do as described to buildings. Of course, this is a mere surmise. I have known in my time many places where hardish clay has prevailed, but I do not re- collect ever seeing buildings crack on it except in mining countries. It would appear that for some hundred years, at least, the ground has been firm, as witness the example of church tower given ; so that the irregular subsidence of the ground is recent—hence my sur- mise. If anything like this be the case the crack- ing will be incurable. The deep trenches for founda- tions, I think, are a mistake, as they thin the clay and of course weaken it. I always consider that if a good foundation can be got at 1}ft. down, it is a waste of both time and materials to go 24hft. If foundations of not very heavy buildings in hardness, concrete is a waste too, I consider. It is for spreading the downward pressure regularly over, which, with uniform moderately hard foundations, will be done without ; but if the effect of concrete still be wanted in shallow cutting put foundations which spread well, and bottom of walls in sand and cement (2 to 1), and fill in with grout, as for walling of sand and cement. If any wide openings, invert from pier to pier if re- quired. This will be found cheaper and better than most concrete, though, after all, from a foot to eighteen inches is thick enough for concrete for any ordinary building, if really good. Drain land well first.—I am, &e., C. A. WEDDLE. Hyde-street, Winchester, Feb. 12. be regular Str,—The account of a difficulty successfully overcome in the course of practice interests most of your readers, and may be of practical use to some who may find themselves in a like position. During last year I had to erect a boathouse, with club-room, offices, &c., partly over the same. The site chosen had formerly been the bed of the river, and not long ago was an ozier holt. An iron rod could be pushed down with perfect ease to a depth of 12ft. from the then surface before it met with any resistance ; it was simply mud deposit. The usual level of the stream was about 4ft. below the land; and after we had taken off about a foot of the top soil, we dug the trenches for the concrete down to the level of the stream till the water just stood in the trench and showed us our required depth all over the site, which was about 65ft. 6in. by 55ft. 6in. After some hesitation, I made up my mind to have the trenches exactly as wide as one- third of the wall height which was to stand over them; andas the 9in. walls were mostly 24ft. high, the concrete was 8{t. wide and 3ft. thick all over the site; and where the wall lowered itself as a lean-to there the concrete tapered to the back trench, which was only 3ft. wide, as the wall was 9ft. high. The first foot in depth of the concrete, all over the site, was mixed with ground lias lime, the rest with local lime. The building was finished two or three months since, and I am happy to say stands ad- mirably. I watched it during its progress, and since completion, and I cannot detect any motion whatever of the slightest description, and the building may be said to float in safety; and as‘the concrete bottom is level with the river, no drought or flood can affect the site; and the vis inertie of the whole mass is also in its favour for future stability. When the trenches were got out I stood ona piece of stone 6ia. by 4in., roughly, say 24in. in area, and after a little time, when I took my weight off and moved the stone, there was a very slight impression in the mud—it was elastic. When I made a calculation of the weight on a given foot of the trench caused by the conerete and the brickwork it was curiously near, not quite so much in proportion as my own weight on the piece ef stone mentioned above, so we know what the mud has to bear, and it does bear it.— Tam, &e., Cambridge. H. G. ELBorne. PLUMBING. S1r,—In reply to “ Plumber” I beg to remind him of an old adage, ‘‘ Never judge a book by its cover.” Even supposing, as he imagines, I sprung from some little corner or sublunary sphere, and admitting your correspondent to be carrying on an extensive business in some large and flourishing part of the globe, I beg to inform him, even in my own county Tcould show him lead work executed in the sixteenth century that would probably foil many a plumber nowadays to excel. I was, however, fortunate enough many years ago to have the supervision of extensive works in London, in the Midland Counties, and some 14,000 miles away, so that your corres- pondent may dispense with the notion’ that I write merely to find fault. I did so because in all my travels I never heard the terms he used ; neither have I read it in Laxton, Gwilt, Dictionary, or Glossary. I at the same time concur with ‘“‘ Plumber” the best way of doing work is the surest, and I repeat that solder should be avoided as far as possible in all external lead work; that flats, gutters, and valleys should not be nailed, for the simple reason of meeting the expansion and contraction of the metal; and in all cases it should be dispensed with as a covering. First, in the case of fire it is highly dangerous ; secondly, because it is liable to be stolen; and thirdly, because it generally requires repairs. And “Plumber” knows as well as I do that with the present supply of every fireproof material and modern advantages, hips, valley ridges, flats, eaves, and down-pipes are in abundance, so that, unless in very extraordi-