Indian Patents. 254068:FOAMING PLASTER

Title of Invention	FOAMING PLASTER
Abstract	A method of producing a foamed plaster comprises the following steps: (a) mixing plaster of Paris and calcium carbonate; (b) supplying water; and (c) adding phosphoric acid. The phosphoric acid reacts with the calcium carbonate to release gaseous carbon dioxide. It also reacts with any steel present to form an insoluble iron phosphate coating.

Full Text	FIELD OF THE INVENTION The present invention relates to foaming plaster and a method of manufacture thereof. SUMMARY OF THE INVENTION In accordance with one aspect of the present invention there is provided a method of producing a foamed plaster, the method characterised by comprising the steps of: (a) mixing plaster of Paris and calcium carbonate, the calcium carbonate being between 2% and 12% by weight of the plaster of Paris; (b) supplying water; and (c) adding phosphoric acid, the phosphoric acid reacting with the calcium carbonate to release gaseous carbon dioxide, and the water providing water of hydration to the plaster of Paris to form gypsum. DESCRIPTION OF PREFERRED EMBODIMENTS In a preferred embodiment of the invention a building panel is formed using the following method. A suitable calcium carbonate containing material is ground to a size of under 50 micron. Suitable calcium carbonate containing materials include limestone, marble, lime sands and coral sands. Preferably the material is predominantly calcium carbonate, with low levels of soluble salts of sodium and magnesium. The ground calcium carbonate is added to powdered plaster of Paris in such quantity that the resulting plaster of Paris and calcium carbonate mixture contains about 6% calcium carbonate by weight. Surface sheeting materials, such as steel, aluminium or flbreglass sheets, are held in frames so as to create a cavity therebetween. The ends of the cavity are sealed by known means. The inner surfaces of the sheeting materials are preferably treated with a bonding agent such as an epoxy primer with glass or other fibre to increase the bond between the sheeting and the plaster. The combined plaster of Paris and calcium carbonate mixture is then combined with 4%w/v phosphoric acid solution in a ratio of about two parts by volume piaster of Paris and calcium carbonate mixture to about one part by volume phosphoric acid solution. A frothing agent may also be added. The resulting suspension is then sprayed or poured into the cavity. In an alternative embodiment, water is added to the mixture in the ratio of about two parts by volume plaster of Paris and calcium carbonate mixture to about one part by volume water. The resulting suspension is then sprayed into the cavity, using an appropriately designed spray head, along with concentrated phosphoric acid. Preferably, the acid has a concentration of about 81% to 85% w/v. In both embodiments, the water present adds water of hydration to the plaster of Paris, thus forming gypsum. At the same time, the phosphoric acid reacts with the calcium carbonate in the limestone according the to the equation in order to liberate carbon dioxide gas. The gypsum sets around the bubbles, forming a foamed plaster. It will be appreciated that the above proportions allow for a surplus of calcium carbonate so that when the reaction above is completed no free acid remains. The hard, foamed plaster produced is comprised predominantly of gypsum together with small amounts of calcium phosphate and remaining calcium carbonate. It will be appreciated that calcium phosphate and calcium carbonate are relatively insoluble, thus allowing for a long life for the foamed plaster. One advantage of the present invention is that the phosphoric acid used during formation of the foamed plaster forms an insoluble iron phosphate coating on any steel sheeting or reinforcing used in connection with the foamed plaster. It will be appreciated that the use of other acids may cause degradation of steel in contact with the foamed plaster. A further advantage of this method is that it is anticipated that over time the calcium phosphate will react with fluoride and/or chloride in the resultant foamed plaster to form apatite, making the structure stronger, and with potentially soluble fluoride and chloride converted to relatively insoluble apatite. It will be appreciated that the method described hereinabove may be varied by the addition of stabilising or strengthening elements to the plaster mix, such as cement or other pozzolanic materials or organic polymers, epoxies and the like. It will also be appreciated that the amount of foaming, and the size of the gaseous bubbles, may be controlled by careful selection of the sizing and amount of calcium carbonate, phosphoric acid and frothing agents used in the above process. It is anticipated that a quantity of calcium carbonate between 2% and 12% by weight of the plaster of Paris will yield a useful result. In another embodiment of the invention, foamed plaster blocks may be formed by combining the equivalent of 8% by weight calcium carbonate with plaster of Paris. This mixture is then added in a rati6 of about two td one by volume with about 5%w/v phosphoric acid, and the resulting the mix sprayed into a box mould. The reaction proceeds as above. When the foamed plaster blocks are formed they can then be cut to a required size. It will be appreciated that foamed plaster made according to the present invention is particularly useful in acting as a fire retardant, and in insulating exposed steel beams on columns. Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. I CLAIM: 1. A method of producing a foamed plaster, the method characterized by comprising the steps of: (a) Mixing plaster of Paris and calcium carbonate, the calcium carbonate being between 2% and 12% by weight of the plaster of Paris; (b) Supplying water; and (c) Adding phosphoric acid, the phosphoric acid reacting with the calcium carbonate to release gaseous carbon dioxide, and the water providing water of hydration to the plaster of Paris to form gypsum, characterized in that water and phosphoric acid are supplied together as dilute phosphoric acid having a concentration of about 5 w/v, or the water is combined with the plaster of Paris and calcium carbonate before the phosphoric acid is added and the phosphoric acid has a concentration of about 81% to 85% w/v. 2. A method of producing a foamed plaster as claimed in claim 1, characterized in that the calcium carbonate is 6% by weight of the plaster of Paris. 3. A method of producing a foamed plaster as claimed in claim 1 or claim 2, characterized in that the calcium carbonate is contained within a calcium carbonate containing material. 4. A method of producing a foamed plaster as claimed in claim 3, characterized in that the calcium carbonate containing material is limestone, marble, lime sands or coral sands. 5. A method of producing a foamed plaster as claimed in claim 3 or claim 4, characterised in that the calcium carbonate containing material is ground to a size of less than 50 micron. 6. A method of producing a foamed plaster as claimed in claim, characterised in that the dilute phosphoric acid solution is supplied in a ratio of about two parts by volume plaster of Paris and calcium carbonate solution to one part by volume dilute phosphoric acid solution. 7. A method of producing a foamed plaster as claimed in claim 1, characterized in that the water is supplied in a ratio of two parts by volume plaster of Paris and calcium carbonate solution to one part by volume water. 8. A method of producing a foamed plaster as claimed in any one of claim 1 to characterised in that the combined water and plaster of Paris mixture are sprayed into a cavity together with a phosphoric acid spray. 9. A method of producing a building panel comprising the steps of holding surface sheeting materials in spaced arrangement so as to form a cavity therebetween; producing a foamed plaster according to the method of any one of claims 1 to, and supplying the foamed plaster into the cavity. 10. A method of producing a foamed plaster block, characterized in that a foamed plaster produced according to claim 1 is sprayed into a box mould. 11. A method of producing a foamed plaster block as claimed in claim 10, characterised in that the calcium carbonate is 8% by weight of the plaster of Paris. 12. A method of producing a foamed plaster block as claimed in claims 10 and 11, characterised in that the water and phosphoric acid are supplied together as 5%w/v phosphoric acid solution. 13. A building panel produced according to the method of claim 9. 14. A foamed plaster block produced according to the method of any one of claims 10 to 12. ABSTRACT FOAMING PLASTER A method of producing a foamed plaster comprises the following steps: (a) mixing plaster of Paris and calcium carbonate; (b) supplying water; and (c) adding phosphoric acid. The phosphoric acid reacts with the calcium carbonate to release gaseous carbon dioxide. It also reacts with any steel present to form an insoluble iron phosphate coating.

Full Text

FIELD OF THE INVENTION
The present invention relates to foaming plaster and a method of manufacture thereof.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention there is provided a method of
producing a foamed plaster, the method characterised by comprising the steps of:
(a) mixing plaster of Paris and calcium carbonate, the calcium carbonate being
between 2% and 12% by weight of the plaster of Paris;
(b) supplying water; and
(c) adding phosphoric acid,
the phosphoric acid reacting with the calcium carbonate to release gaseous carbon
dioxide, and the water providing water of hydration to the plaster of Paris to form
gypsum.
DESCRIPTION OF PREFERRED EMBODIMENTS
In a preferred embodiment of the invention a building panel is formed using the
following method.
A suitable calcium carbonate containing material is ground to a size of under 50
micron. Suitable calcium carbonate containing materials include limestone, marble,
lime sands and coral sands. Preferably the material is predominantly calcium

carbonate, with low levels of soluble salts of sodium and magnesium. The ground
calcium carbonate is added to powdered plaster of Paris in such quantity that the
resulting plaster of Paris and calcium carbonate mixture contains about 6% calcium
carbonate by weight.
Surface sheeting materials, such as steel, aluminium or flbreglass sheets, are held in
frames so as to create a cavity therebetween. The ends of the cavity are sealed by
known means.
The inner surfaces of the sheeting materials are preferably treated with a bonding
agent such as an epoxy primer with glass or other fibre to increase the bond between
the sheeting and the plaster.
The combined plaster of Paris and calcium carbonate mixture is then combined with
4%w/v phosphoric acid solution in a ratio of about two parts by volume piaster of
Paris and calcium carbonate mixture to about one part by volume phosphoric acid
solution. A frothing agent may also be added. The resulting suspension is then
sprayed or poured into the cavity.
In an alternative embodiment, water is added to the mixture in the ratio of about two
parts by volume plaster of Paris and calcium carbonate mixture to about one part by
volume water. The resulting suspension is then sprayed into the cavity, using an
appropriately designed spray head, along with concentrated phosphoric acid.
Preferably, the acid has a concentration of about 81% to 85% w/v.
In both embodiments, the water present adds water of hydration to the plaster of Paris,
thus forming gypsum. At the same time, the phosphoric acid reacts with the calcium
carbonate in the limestone according the to the equation

in order to liberate carbon dioxide gas. The gypsum sets around the bubbles, forming
a foamed plaster.
It will be appreciated that the above proportions allow for a surplus of calcium
carbonate so that when the reaction above is completed no free acid remains. The
hard, foamed plaster produced is comprised predominantly of gypsum together with
small amounts of calcium phosphate and remaining calcium carbonate. It will be
appreciated that calcium phosphate and calcium carbonate are relatively insoluble,
thus allowing for a long life for the foamed plaster.
One advantage of the present invention is that the phosphoric acid used during
formation of the foamed plaster forms an insoluble iron phosphate coating on any
steel sheeting or reinforcing used in connection with the foamed plaster. It will be
appreciated that the use of other acids may cause degradation of steel in contact with
the foamed plaster.
A further advantage of this method is that it is anticipated that over time the calcium
phosphate will react with fluoride and/or chloride in the resultant foamed plaster to
form apatite, making the structure stronger, and with potentially soluble fluoride and
chloride converted to relatively insoluble apatite.
It will be appreciated that the method described hereinabove may be varied by the
addition of stabilising or strengthening elements to the plaster mix, such as cement or
other pozzolanic materials or organic polymers, epoxies and the like. It will also be
appreciated that the amount of foaming, and the size of the gaseous bubbles, may be
controlled by careful selection of the sizing and amount of calcium carbonate,
phosphoric acid and frothing agents used in the above process. It is anticipated that a

quantity of calcium carbonate between 2% and 12% by weight of the plaster of Paris
will yield a useful result.
In another embodiment of the invention, foamed plaster blocks may be formed by
combining the equivalent of 8% by weight calcium carbonate with plaster of Paris.
This mixture is then added in a rati6 of about two td one by volume with about 5%w/v
phosphoric acid, and the resulting the mix sprayed into a box mould. The reaction
proceeds as above. When the foamed plaster blocks are formed they can then be cut to
a required size.
It will be appreciated that foamed plaster made according to the present invention is
particularly useful in acting as a fire retardant, and in insulating exposed steel beams
on columns.
Modifications and variations as would be apparent to a skilled addressee are deemed
to be within the scope of the present invention.

I CLAIM:
1. A method of producing a foamed plaster, the method characterized by comprising the
steps of:
(a) Mixing plaster of Paris and calcium carbonate, the calcium carbonate being between
2% and 12% by weight of the plaster of Paris;
(b) Supplying water; and
(c) Adding phosphoric acid,
the phosphoric acid reacting with the calcium carbonate to release gaseous carbon
dioxide, and the water providing water of hydration to the plaster of Paris to form
gypsum, characterized in that water and phosphoric acid are supplied together as dilute
phosphoric acid having a concentration of about 5 w/v, or the water is combined with the
plaster of Paris and calcium carbonate before the phosphoric acid is added and the
phosphoric acid has a concentration of about 81% to 85% w/v.
2. A method of producing a foamed plaster as claimed in claim 1, characterized in that the
calcium carbonate is 6% by weight of the plaster of Paris.
3. A method of producing a foamed plaster as claimed in claim 1 or claim 2, characterized
in that the calcium carbonate is contained within a calcium carbonate
containing material.
4. A method of producing a foamed plaster as claimed in claim 3, characterized in that the
calcium carbonate containing material is limestone, marble, lime sands or
coral sands.
5. A method of producing a foamed plaster as claimed in claim 3 or claim 4, characterised
in that the calcium carbonate containing material is ground to a size of less than 50
micron.
6. A method of producing a foamed plaster as claimed in claim, characterised in
that the dilute phosphoric acid solution is supplied in a ratio of about two parts
by volume plaster of Paris and calcium carbonate solution to one part by
volume dilute phosphoric acid solution.

7. A method of producing a foamed plaster as claimed in claim 1, characterized
in that the water is supplied in a ratio of two parts by volume plaster of Paris
and calcium carbonate solution to one part by volume water.
8. A method of producing a foamed plaster as claimed in any one of claim 1 to
characterised in that the combined water and plaster of Paris mixture are
sprayed into a cavity together with a phosphoric acid spray.
9. A method of producing a building panel comprising the steps of holding
surface sheeting materials in spaced arrangement so as to form a cavity
therebetween; producing a foamed plaster according to the method of any one
of claims 1 to, and supplying the foamed plaster into the cavity.
10. A method of producing a foamed plaster block, characterized in that a foamed
plaster produced according to claim 1 is sprayed into a box mould.
11. A method of producing a foamed plaster block as claimed in claim 10,
characterised in that the calcium carbonate is 8% by weight of the plaster of
Paris.
12. A method of producing a foamed plaster block as claimed in claims 10 and
11, characterised in that the water and phosphoric acid are supplied together
as 5%w/v phosphoric acid solution.
13. A building panel produced according to the method of claim 9.
14. A foamed plaster block produced according to the method of any one of
claims 10 to 12.

ABSTRACT

FOAMING PLASTER
A method of producing a foamed plaster comprises the following steps: (a) mixing plaster of
Paris and calcium carbonate; (b) supplying water; and (c) adding phosphoric acid. The
phosphoric acid reacts with the calcium carbonate to release gaseous carbon dioxide. It also
reacts with any steel present to form an insoluble iron phosphate coating.

FOAMING PLASTER

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