Bourne Archive:
Brees: Lime mortar
http://boar.org.uk/aaiwxw3BreesLime.htm Latest edit 7 Mar
2010
The Bourne Archive
The Architectural and Engineering Glossary of S.C. Brees (1852)
Extracts Concerning Lime Mortar.
pp. 252-4
LIME, a valuable
substance much used in building, and for other purposes, being the most
essential ingredient in all cements; it forms one of the primitive earths,
although never found native or in a state of purity, but it is always combined
with acids which exist in prodigious quantities in it; marble, limestone and
chalk, are all carbonates of lime, and gypsum is sulphate of lime. Lime may be
prepared from any carbonate of lime, as limestone or chalk, calcined or well
burnt in kilns for some time to a white heat, by which the carbonic acid and
acid contained in those substances are expelled, and the earth left in a
fragile mass with very little coherence, having lost nearly 44 per cent. of its
weight; it may now be easily reduced to a powder, when it is called quick lime, in which state it shows a
great disposition for water, upon applying which it instantly swells and
cracks, producing a considerable degree of heat (it will absorb one-fourth of
its weight in water, and yet appear dry), it then falls into a fine white
powder, when it is called slaked lime,
having about double its former bulk.
Stone lime is
generally used in extensive buildings, and the quality of the lime is supposed
by many to be in proportion to the hardness of the stone from which it is
produced. Brown stone lime is said to be the best for all kind of cements,
although blue lias lime is considered by some to be superior, as it withstands
the action of water exceedingly well; it was used by Mr. Smeaton
in building the Eddystone lighthouse, where it succeeded after all
other descriptions of lime had failed. Good chalk lime, although said to be
inferior to stone, is yet much esteemed. Lime should always be kept under an
enclosed shed, particularly chalk lime, as it suffers particularly from
exposure to the air: the efficacy of lime also depends on being well burnt,
after which process it should be used as soon as possible.
LIME AND HAIR, a
mixture of lime and hair, and employed with the plaster in first coats and
floating; a greater quantity of hair is used in the latter than in the former.
It is also sometimes called coarse stuff.
LIME CORE, the
coarse lumps of extraneous matter and inefficiently burnt stone lime, which do
not pass through the screen in the operation of screening.
Lime core is unfit
for making cement and mortar, but it is very serviceable as dry filling at the
backs of walls and under floors and paving.
LIME KILN, a kiln
employed in burning limestone, shells, and other calcareous matter.
The most simple kind
of lime kiln consists of a hole dug in the ground in the shape of an inverted
cone, and situated on the top of a high bank, in order to admit of the
materials being put in at the top, and taken out at the bottom. The sides may
be built up in bricks or sods, or left naked, according to the nature of the
ground. The limestone properly broken is spread in alternate layers with coal
of furze, the top being covered with sods, and 1 bushel of coals produces about
3 of lime. The fire is lighted at the bottom, where a door is left to remove
the lime and admit a draught to the interior. The better sort of lime kilns are
formed in the shape of a hogshead or an egg broken off square at each end, and
compressed a little at the base to an oval shape, with an eye, or draft-hole,
at each end of it. There is an inside and outside wall, a layer of clay, 2 feet
in thickness, being interposed between them. A metal plate below receives the
materials, admits the draught, and facilitates the discharging. These are
constantly burning, and are distinguished by the name of draw-kilns.
LIME STONE, the
stone from which lime is produced; the most crystalline marble, all calcareous
stone, as well as chalk, being composed of lime. Every stone, in fact, which
will ferment with an acid (as aqua fortis) is capable of being burnt into lime,
and the harder the stone the better will be the lime. Limestone is of various
colours, as brown, blue, grey, red, yellow, and green. When any of these are
combined, it is called marble. The
limestones found in this country are mostly either of a yellowish red or
blueish cast.
The limestones used
for building are classified into three, - 1st, the pure limestone, which
contain from 79 to 93 of carbonate of lime; 2ndly, the oolite, containing about
the same quantity; and 3rdly, the magnesian limestone. The Balsover,
[Anston
stone from grid ref. SK 5282] of which the new Houses of Parliament
are built, is at the head of this class, and contains 51.1 of carbonate of
lime, 40.2 of carbonate of magnesia, and 3.6 of silica. The cohesive powers of
the Balsover are upwards of five times as great as the
pp. 284-5
MORTAR, a cement
used for building purposes, composed of lime, sharp coarse sand, and the hair
of cattle, which should be thoroughly mixed together in a pug mill, or well
tempered with wooden beaters, with a small portion of water, in the proportion
of 1 of lime to 2 of sand, well chafed. The lime should be used as fresh and
stiff as possible, and it ought to be kept under an enclosed shed. The bricks
or stones should, if possible be well saturated with water, particularly in hot
weather.
Twenty-seven cubic
feet make 1 load of mortar, which contains a hundred of lime, and a
proportionate quantity of sand; and a hod is 9 inches by 9 inches, and 14
inches long; 2 hods of mortar make nearly 7 bushels.
No more than about a
bushel of lime should be slaked at one time, and no more water should be
employed than is required to reduce it to powder, when it ought to be
immediately covered with sand to prevent the gas escaping, which constitutes
its indurating quality. The mortar should be beaten three or four times over,
so as to incorporate the lime and sand together, and to break any pieces of
lime that may have passed through the sieve, the operation being performed with
scarcely any water. This improves the strength of the mortar considerably. If
the mortar is laid by for any time, it ought to be beaten up again before being
used, to save the time of the bricklayer, and is should be used soft in summer,
and rather stiff in wintry weather.
The ruins found at
When a small drop of
water is exposed to the air, the calcareous matter contained in it begins to
separate from the water, and to reassume its native form of limestone or
marble, and upon the calcareous matter being perfectly crystalized, it becomes,
in fact, limestone or marble, of the same consistence as before. The perfection
of the cement must, therefore, depend entirely upon the perfection of the
crystals. That the crystalization may be more perfect, it has been recommended
to mix the ingredients well together with a large quantity of water, and allow
the drying to be as slow as possible/ The middle of the old Roman walls was
composed of pebbles thrown in at random, and some think that the mortar must
have been liquid, so as to have been poured in among them. This would have the
effect of dissolving a large quantity of the lime, and thus render the
crystalization very perfect, so that the mortar would become as hard as the
stones themselves.
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