AN IMPROVED PLASTER ADAPTED FOR CASTS OR MOULDINGS, THE COATING OF WALLS, AND FOR ANALOGOUS PURPOSES
Year: 1882

page_text: LETTERS PATENT to Philip Middleton Justice, of 14, Southampton Buildings,
in the County of Middlesex, Patent Agent, for an invention of "AN IMPROVED
PLASTER ADAPTED FOR CASTS OR MOULDINGS, THE COATING OF WALLS, AND
FOR ANALOGOUS PURPOSES."-A communication from abroad by Melvin
Batchlor Church, of Grand Rapids, County of Kent, State of Michigan,
United States of America.
PROVISIONAL SPECIFICATION left by the said Philip Middleton Justice at
the Office of the Commissioners of Patents on the 4th April 1882.
PHILIP MIDDLETON JUSTICE of 14 Southampton Buildings, in the County of
Middlesex Patent Agent. "AN IMPROVED PLASTER ADAPTED FOR CASTS OR MOULDINGS,
THE COATING OF WALLS, AND FOR ANALOGOUS PURPOSES." A communication from
abroad by Melvin Batchlor Church, of Grand Rapids, County of Kent, State of
Michigan, United States of America.
This Invention is an improved plaster adapted for casts or mouldings and for
coating and finishing the walls of rooms and other surfaces. The principal
ingredient of this improved plaster is calcined gypsum in a very finely divided
condition, and in connection with the gypsum a small quantity of glue is also
used. Glue has heretofore been used in connection with finely pulverized calcined
gypsum as a covering for walls, in which the principal office of the glue was to
retard the setting process while the compound was held in liquid form during the
process of covering the walls, the glue also serving in addition to this to harden the
gypsum. The object of this invention is to improve the compound of gypsum and
glue, as it has been applied to walls, and at the same time to render the same
compound practically applicable to the formation of casts or other moulded forms."
First in respect to the compound as heretofore used for covering walls or other
surfaces, the absorption of the glue by the gypsum was never perfect and varied
greatly with varying differences of the temperature, so that often by reason of the

page_text: non absorption of the glue, the compound would have the imperfect texture of a
glue mixed with an inert powder, such as whiting or Paris white, in which no
chemical change or combination ensues, by which the glue ceases to exist in its
original form and nature. A further difficulty has also been experienced in
covering the walls of rooms with a number of coats, arising out of the retarding
action of the glue continuing after the material has been spread upon the wall.
This is such that several days must be allowed to clapse after applying the first
coat, before the second can be applied in order to give the first coat time to harden,
and prevent it from being cut through by the brush in applying the second coat,
by which a rough and uneven surface would be produced. This composition of
glue and gypsum bas been found practically useful for the purpose for which it was
intended, but under certain circumstances, principally of differences of temperature,
these defects have impaired the usefulness of the article It has been impracticable
to use the plaster and glue in a plastic form for making moulded articles, for the
reason that the plaster would not set with sufficient readiness In order to remedy
all these difficulties I have found that some substance should be added to the
gypsum and glue, which upon exposure to the atmosphere would cause the glue to
be absorbed more readily by the gypsum and would neutralize to some extent the
retarding effect of the glue in respect to the setting of the plaster I have discovered
after much study and experiment, that these desired results can be accomplished
by adding to the compound of gypsum and glue, a small proportion of sulphate of
zinc It will be understood that the gypsum and the glue must be in a very finely
divided condition, and that the sulphate of zinc must be thoroughly and uniformly
mixed with these ingredients The substance may be mixed in a dry condition,
and any suitable colouring matter may be mixed therewith. The proportions 1
use are from five to eight pounds of the best glue with from one to one and a half
pounds of sulphate of zinc, to each hundred pounds of the plaster.
As before stated the materials may all be mixed in a dry and powdered
condition, or the glue and sulphate of zinc may be dissolved in water and the
gypsum subsequently added.
This composition when applied to walls, or like surfaces will set in suitable time
to leave the whole in a good condition, that is to say, not so soon as to include
unabsorbed water which would give a dark appearance, but with sufficient rapidity
to allow the workman to proceed as soon as it has dried (ordinarily in an hour or
two) to apply another coat Any number of coats may be applied to the same
surface, and the whole will assume a perfectly homogeneous condition throughout
solid and free from any tendency to scale, and free from any unabsorbed glue. As
the sulphate of zinc serves the double purpose of neutralizing the retarding effect
of the glue upon the setting of the plaster, and of adding to the hardness of the
material when set, it will be apparent that when the material is to be used in a
plastic state for formning casts or any moulded forms, where a very hard and quick
setting cement is required, the proportions of the sulphate of zine must be varied.
Although no very exact limits need be set about twice the relative amount hereto-
fore specified of the sulphate of zine may be used in connection with the plaster
and glue The workman can vary the amount as he desires it to set faster or
slower without material variation in the product. Some variation may also be
made in the proportion of the glue. In applying this material to walls by means of
a brush under ordinary conditions of temperature I take four measures of the three
specified materials mixed and in a loose condition. This I dissolve in three measures
of very hot water and to the solution add two measures of cold water when the
material is ready to be applied to the wall. Only so much should be dissolved at
a time as is needed for use for the day and the material after being mixed should
not be allowed to stand more than an hour without stirring.
:
In extremely hot weather for the first coat the two measures of cold water
should be omitted and the mixture applied to form the first coat. The second coat
may be the same as that first described.

page_text: When the material is to be used in a plastic condition sufficient water only is
required to reduce the material to that condition and in that case the water should
all be hot. Other mineral salts may be used instead of the sulphate of zinc, that
is to say those of like character but I believe the sulphate of zinc to be the best
I have tried copperas with good results, except that the colour which it imparts is
objectionable.
For the best results I use a pulverized gypsum carefully reground and reduced
not only to great fineness but also to uniformity of fineness. Calcined gypsum
ground by the ordinary methods and bolted, is liable to be made up of particles of
different size, and these different grades of particles constantly tend to arrange
themselves according to their gravity and the larger settle to the bottom, which
interferes with the perfect uniformity of work.

page_text: SPECIFICATION in pursuance of the conditions of the Letters. Patent filed
by the said Philip Middleton Justice in the Great Seal Patent Office on the
31st August 1882.
PHILIP MIDDLETON JUSTICE of 14 Southampton Buildings in the County of
Middlesex Patent Agent "AN IMPROVED PLASTER ADAPTED FOR CASTS OR
MOULDINGS, THE COATING OF WALLS, AND FOR ANALOGOUS PURPOSES
A coin-
munication from abroad by Melvin Batchlor Church of Grand Rapids County
of Kent, State of Michigan United States of America
This Invention relates to an improved plaster adapted for casts or mouldings and
for coating and finishing the walls of rooms and other surfaces. The principal
ingredient of this improved plaster is calcined gypsum in a very finely divided
condition and in connection with the gypsum a small quantity of glue is also added.
Glue has heretofore been used in connection with finely pulverized calcined gypsum
as a covering for walls in which the principal office of the glue was to retard the
setting process, while the compound was held in liquid form during the process of
covering the walls the glue also serving in addition to this to harden the gypsum.
The object of this invention is to improve the compound of gypsum and glue, as it
has been applied to walls and at the same time. to render the same compound
practically applicable to the formation of casts or other moulded forms. First in
respect to the compound as heretofore used for covering walls or other surfaces the
absorption of the glue by the gypsum was never perfect and varied greatly with
varying differences of the temperature so that often by reason of the non absorption
of the glue the compound would have the imperfect texture of a glue mixed with
an inert powder such as whiting or Paris white in which no chemical change or
combination ensues by which the glue ceases to exist in its original form and
nature. A further difficulty has also been experienced in covering the walls of
rooms with a number of coats arising out of the retarding action of the glue
continuing after the material has been spread upon the wall. This is such that
several days must be allowed to elapse after applying the first coat before the
second can be applied in order to give the first coat time to harden and prevent it
from being cut through by the brush in applying the second coat, by which a rough
and uneven surface would be produced This composition of glue and gypsum has
been found practically useful for the purpose for which it was intended but under
certain circumstances principally of differences of temperature these defects have
impaired the usefulness of the article It has been impracticable to use the plaster
and glue in à plastic form for making moulded articles, for the reason that the
plaster would not set with sufficient readiness In order to remedy all these
difficulties I have found that some substance should be added to the gypsum and
glue, which upon exposure to the atmosphere would cause the glue to be absorbed
more readily by the gypsum and would neutralize to some extent the retarding
effect of the glue in respect to the setting of the plaster. I have discovered after
much study and experiment that these desired results can be accomplished by
adding to the compound of gypsum and glue a small proportion of sulphate of zinc
It will be understood that the gypsum and the glue must be in a very finely divided
condition and that the sulphate of zinc must be thoroughly and uniformly mixed
with these ingredients The substance may be mixed in a dry condition and any
suitable colouring matter may be mixed therewith The proportions I use are from
five to eight pounds of the best glue with from one to one and a half pounds of
sulphate of zinc to each hundred pounds of the plaster As before stated the
materials may all be mixed in a dry and powdered condition, or the glue and

page_text: sulphate of zinc may be dissolved in water and the gypsum subsequently added
This composition when applied to walls or like surfaces will set in suitable time to
leave the whole in a good condition, that is to say not so soon as to include
unabsorbed water, which would give a dark appearance but with sufficient rapidity
to allow the workman to proceed as soon as it has dried (ordinarily in an hour or
two) to apply another coat Any number of coats may be applied to the same
surface and the whole will assume a perfectly homogeneous condition throughout,
solid and free from any tendency to scale and free from any unabsorbed glue.
As the sulphate of zinc serves the double purpose of neutralizing the retarding
effect of the glue upon the setting of the plaster and of adding to the hardness of
the material when set, it will be apparent that when the material is to be used in a
plastic state for forming casts or any moulded forms, where a very hard and quick
setting cement is required, the proportions of the sulphate of zinc must be varied.
Although no very exact limits need be set about twice the relative amount
beretofore specified of the sulphate of zinc may be used in connection with the
plaster and glue The workman can vary the amount as he desires it to set faster
or slower without material variation in the product Some variation may also be
made in the proportion of the glue In applying this material to walls by means of
a brush under ordinary conditions of temperature I take four measures of the
three specified materials mixed and in a loose condition This I dissolve in three
measures of very hot water and to the solution add two measures of cold water
when the material is ready to be applied to the wall. Only so much should be
dissolved at a time as is needed for use for the day and the material after being
mixed should not be allowed to stand more than an hour without stirring.
In extremely hot weather for the first coat the two measures of cold water
should be omitted and the mixture applied to form the first coat The second coat
may be the same as that first described When the material is to be used in a
plastic condition sufficient water only is required to reduce the material to that
condition and in that case the water should all be hot Other mineral salts may be
used instead of the sulphate of zinc that is to say those of like characters, but I
believe the sulphate of zinc to be the best I have tried copperas with good results
except that the colour which it imparts is objectionable For the best results
I use a pulverized gypsum carefully reground and reduced not only to great
fineness but also to uniformity of fineness Calcined gypsum, ground, by the
ordinary methods and bolted is liable to be made up of particles of different size
and these different grades of particles constantly tend to arrange themselves
according to their gravity and the larger settle to the bottom which interferes with
the perfect uniformity of work. Having thus described the invention of my
foreign correspondent What I claim and desire to secure by Letters Patent is
The described compound consisting of pulverized calcined gypsum, glue, and
sulphate of zinc or its equivalent in substantially the proportions specified.
In Witness whereof I the said Philip Middleton Justice have hereunto set
my hand and seal this thirty first day of August in the year of Our Lord
one thousand eight hundred and eighty two.
Signed sealed and delivered
in the presence of
ALLEN PARRY JONES
53 Chancery Lane
London W.C.
PHILIP M. JUSTICE. (L.S.)