Improvements in Plaster for Building Purposes.
Year: 1892

page_text: COMPLETE SPECIFICATION.
Improvements in Plaster for Building Purposes.
I, THOMAS JONES, of East Ravenswood Park, Chicago, Illinois, United States
of America, Manufacturer, do hereby declare the nature of this invention and in
what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement :-
The unsatisfactory results obtained by the use of common lime mortar for covering
wooden surfaces are too well known to need specific mention.
It is the object of my invention to avoid the defects of such plaster and to
produce a material which will attain the utmost hardness and possess great
tenacity at such moderate cost as to make it available generally as
covering.
a wall
In a former U.S. Patent No. 451,560, dated May 5, 1891, I have specified the
use of granite as an active and important ingredient in a wall plaster; but the
difficulty of procuring granite in some localities and the cost of reducing it to a
suitable condition for use tend to limit is usefulness and availability for the
purpose.
An object of my present invention is to produce a wall plaster equal if not
superior to the plaster described in said Patent at a less cost.
I therefore employ a material in lieu of the granite which is more extensively
distributed and in most places easily accessible, and by means of which I attain
the necessary hardness and tenacity in the plaster when said new ingredient is
treated and compounded with other ingredients as herein described.
To this end I first take gypsum rock and calcine it in a suitable kiln or oven,
at a bright red heat, for one hour or thereabouts, to destroy its quick-setting
properties; when cool it is ready for mixture with the other ingredients of my new
plaster.
I take aluminous shale or alkaline clay, of the coal measures, selecting those
containing the least percentage of iron and the largest percentage of alkali
(potash). These I calcine at a low red heat until they assume a light color, and
until the carbonaceous matter contained therein is destroyed. I then grind these
to a fine powder which is placed in a suitable vessel and to every 100 pounds of
said powder I add about 33 pounds of sulphuric acid, of ordinary commercial
quality, and dilute with four or five times its bulk of water. I then boil the
mixture for ten or twelve hours or longer, adding water from time to time to
supply that lost by evaporation. It is then removed from the vat and allowed to
dry, when it is fit for mixing with the over calcined plaster or gypsum. If, however
the shale or clay contains less than six per cent. of alkali (potash) I add enough of
a salt of that substance (crude potash preferred) before withdrawing from the
tank, to supply the deficiency and bring it up to that standard of strength; and
I then stir up the mixture until the potash is thoroughly incorporated with and
diffused through the mass, which is then withdrawn from the tank and allowed to
dry, as before described. I then grind up together the over calcined gypsum and
the mixture of shale or clay powder treated with sulphuric acid as described, in
the proportion of 15 to 20 parts by weight of the shale mixture to 100 parts by
weight of the gypsum, and when thoroughly mixed together and bolted it is ready
for use.
To apply the plaster to walls or ceilings I mix the plaster with an equal bulk
of sand, and add water sufficient to make it plastic and then apply in the usual
way. It may be finished in one or more coats. If two coats are intended, I allow
the first coat to become dry and then mix my plaster with an equal bulk of lime
putty, and add enough water to bring the mass to a proper consistency, then apply
in all respects in the same manner as ordinary plaster "finish."

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. As a composition of matter, a plaster composed of shale or clay, potash,
sulphuric acid and gypsum, in about the proportions stated.
2. The herein described process for the production of plaster, consisting in
mixing together shale or clay, (containing or having added thereto potash) which
has been treated with dilute sulphuric acid and over calcined gypsum, in about the
proportions stated.
Dated this 11th day of October 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.