"DAMP WALLS," OR "STONE v. WOOD."

New Zealand Herald, Volume XII, Issue 4399, 18 December 1875, Page 1 (Supplement)

"DAMP WALLS," OR "STONE v. WOOD."

To the Editor of the Herald. Sib, —With your permission, I will state some facts -which may help to explain the cause of " Damp Walls," so far only, when the cause ia evidently in the materials used in them. A circumstance came under my notice in England, in which the use of salt in the glazing of bricks which had some chalk in their composition, or more correctly, the chalk was ground in the wash-mill with the clay, till it'was thin as water. I believe the chemical combination formed by the action of the salt in glazing would cause the brick to efflorest—it even came through the plaster ; that cause was clearly in the brick, and not in the mortar. Walls facing the sea at Southampton are many of them faced with slate, because the continuous damp sea air laden with saline matters penetrates through the soft brick from end to end. The cause of this was the bad quality of the brick used ; —a good London brick would have effectually preserved the plaster inside from being affected. Building materials of any description, which have been subjected to the action of salt water cannot be deprecated too much. Their use in dwelling buildings must; be sternly prohibited; —there is no necessity now for their use. We have in pozzolana, which is as Vitruaries describes, "A sort of cindery earth burnt by fire, inclosed in the mountains, which suddenly knits together, in water, and makes a building very strong." Only roach (or unslaked) lime should be used, and the lime always slaked -with/Ve.sA water. The lime should always be tested. One bashel of oyster shell lime, strike measure, well burnt, will plimp, plump, or swell to one and three-quarter bushels, strike measure, which passed through sieve of 144 moashes to the square inch, only about one pint of refuse or unburnt shell as a residue should be the result. Stone lime should yield no more residue. Only tempered mortar should be used. Where it is merely to be hand-tempered no more useless or unfit instrument could be derised than the round or hollow shovel; it is the best known tool to make the true "untempered mortar" with. With machinery for tempering mortar we should have as good as any in the world. I believe that the cindery sand obtaiuable in our mountains is precisely the pozzolana of the Romans. Sir William Martin informed me many years ago that, when he was travelling in Italy, he was informed that in the caves explored were found perforated copper sieves evidently used for sifting the pozzolana. The very best pozzolana I have always got off the Rtmuera Boads, especially from the road leading to the Orakei Bridge. The Maoris contrasted for making the road, and got the rough scoria from a small mountain near the road. With regard to what is lime, I hold the opinion that lime is the same thing all the world over, —simply shell. So well was the meaning or value of the word tempering, as required to make good mortar, understood that it was a usual thing to say to a learner, " You wdll spoil it if you temper it too much," meaning it was impossible to temper it too much. I would therefore recommend to those who have the opportunity of knowing by testing what is the best or correct time required by a tempering machine, and by experiment, learn when it has had sufficient manipulation, and if it can be too intimately mixed. As a finish to this, I strongly advise that the words 'near enough" and their meaning be not allowed in any cood building.—l am, &c., J. B. Strange.