Ashtech Gypsum Plaster
By :- CA UMESH KUMAR BANGUR
The word gypsum is derived from the Greek word gypsos, i.e. "chalk" or "plaster". Because gypsum from
the quarries of the Montmartre district of Paris have long furnished burnt gypsum (calcined gypsum)
used for various purposes, this hemihydrate gypsum became known as PLASTER OF PARIS .
Upon addition of water, after a few tens of minutes plaster of Paris becomes regular gypsum (dihydrate)
again, causing the material to harden or "set" in ways that are useful for casting and construction. It can be
used as a fertilizer , is the main constituent in many forms of plaster and is widely mined.
There are four different varieties of Gypsum, all are composed of Calcium sulfate dihydrate (meaning 2
molecules of water. Its Chemical formula is CaoSo4 2H2O.
Gypsum occurs in nature as flattened
and often twinned crystals and
transparent cleavable masses called
significant selenium; rather both
substances were named from the
Ancient Greek word for the Moon.
Selenite may also occur in a silky,
fibrous form, in which case it is
commonly called satin spar.
• In India, Rajasthan is the greatest
producer of Gypsum minerals.
The state also accounts for 94% of
gypsum, Rajasthan has the highest
number of mine leases in India 1,324 leases for major minerals.
• The following table shows the share of
Rajasthan in terms of reserve and
production of the Gypsum minerals:-
District Wise Distribution
Mineral Deposits Distribution
Phosphogypsum is a the primary byproduct of the wet-acid process for producing phosphoric acid
from phosphate rock. The production of each ton of phosphoric acid is accompanied by the
production of 4½ tons of the by-product calcium sulfate, also known as phosphogypsum.
Phosphogypsum is a radioactive waste product that results from processing phosphate ore to
make phosphoric acid that is later used in fertilizer. Because the phosphate ore contains uranium
and radium, phosphogypsum also contains these radionuclides. The radium is of particular
concern because it decays to form radon, a cancer-causing, radioactive gas. Phosphogypsum has
few uses and is disposed of in large, aboveground stacks.
Phosphate rock, which is processed to make phosphoric acid, contains concentrations of naturally
occurring radioactive elements (radionuclides). Even high grade ores, which contain about 70%
calcium phosphate, also contain a large number of impurities, such as calcium fluoride, chlorides,
chromium, rare earths, and radionuclides. At the end of the production process, the radionuclides
end up in the phosphogypsum.
Manufacturing Process Phosphogypsum
Rock phosphates used for production of phosphoric acid contain small
concentrations of radioactive nuclides, viz., Uranium-238 and Radium-226.
Phosphogypsum contains activity concentration of U-238 typically in the range
0.1-0.2 Bq/g and Ra-226 typically in the range 0.5-1.3 Bq/g.(Bq is a unit of
Radioactivity is in the phosphogypsum?
The concentrations of uranium-238 and radium-226 in phosphogypsum samples
taken in were about 10 times the background levels in soil for uranium and 60
times the background levels in soil for radium 226.
The radium-226 concentration in phosphogypsum varies significantly at different
sampling locations on a single stack and also in phosphogypsum from different
stacks within the same geographical area.
People exposed to the radiation from Phosphogypsum?
Radionuclides that are small particles (i.e., radionuclide dust) can become airborne as wind-blown
dust. The Radionuclides, uranium 238 and radium-226, are present in the phosphogypsum and can
become airborne. Once these radionuclides are in the air, people and animals can breathe them and
they can settle out onto ponds and agricultural areas. Radon-222, a decay product of radium-226, is a
gas and so may become airborne by diffusing into the air ( a cancer-causing, radioactive gas)
Based on the principal followed internationally , the Atomic Energy Regulatory Board (AERB) has issued a
safety directive on the use of phosphogypsum.
However some of the manufacturers of Gypsum Plaster fails to follow the same .
• Gypsum rocks are sedimentary rocks
made up of sulfate mineral and formed
as the result of evaporating sea water in
massive prehistoric basins
Imported Gypsum (Rock Gypsum) are
High Quality White Gypsum, more pure
and its crystals are more prismatic than
mining Gypsum .
When mixed with water, form a much stronger and harder Gypsum plaster.
Microstructure – High Strength Gypsum Plates
Gypsum Application Area
Benefits Of Gypsum Plaster
FOR BUILDERS & DEVELOPERS:
1. Green material
2. Shrinkage crack free surfaces - smooth finish
3. High productivity – faster work (Reducing plastering time by 70% when compared to conventional Sand
cement plaster + POP method) so time saving
4. Performance – Durability, light weight (Reduces dead load on structure)
5. Cleaner sites - direct application bagged product – requires no water curing
FOR END CUSTOMERS:
1. No shrinkage cracks on walls and ceilings
2. Reduction in the time required for plastering and this helps in timely possession of homes
3. Perfectly lined, leveled, smooth walls
4. Saving on electricity used for air conditioning as gypsum has very low thermal conductivity.
Advantages of One Coat Gypsum Plaster
Direct Application: One coat application directly on brick, block & concrete walls
No water curing required
Free of shrinkage cracks and better resistance to water
Time saving: Results in substantial time saving as compared to conventional
Easy to apply: Simple mixing of water to the product is required
Superior heat and sound insulation properties due to special additives
The Value Proposition
Line & Level
Sand Cement Plaster
One Coat Plaster
Ashtech’s High Graded Gypsum Plaster
Looking to the huge demand of the Gypsum plaster for internal walls & celling, the Ashtech
(India) Pvt. Ltd have introduced a high graded Gypsum plaster namely:VEGA GYPSUM PLASTER-IMPORTED
Ashtech Vega gypsum is super white high grade Gypsum confirming to international standard.
Compressive Strength 12.2 Mpa .
REVA GYPSUM PLASTER-DOMESTIC
Ashtech REVA gypsum is high grade domestic Gypsum Plaster confirming to Indian standard, IS
2547(part I & part II ).
Compressive Strength 10.7 Mpa .
Ashtech Gypsum gives excellent strength and Bonding due to its high compressive strength.
It has Good aesthetics finish due to better fineness.
More durable & long lasting due to high purity.
Very economical due to ease in workability and less wastage.
Strength properties of Gypsum Plaster
•Strength properties of hardened Gypsum Plaster is measured as
Transverse Strength and Compressive strength.
•As per IS 2547 (part-I) minimum transverse strength of Gypsum
Plaster required to be 5 kg/cm2.
•Compressive strength of Gypsum Plaster is its indexing property as
Plaster has its maximum strength against compression.
•As per IS 2547(part-II) minimum compressive strength for under
coat plaster required to be 1 N/ mm2
•1 N/ mm2 = 1 Mpa and
•1 kg/cm² = 0.098 Mpa (Source: theunitconverter.com)
•Therefore higher the compressive strength of Gypsum Plaster,
higher the Transverse /shear/ bonding strength .
Test Lab Certificates
Lower the Compressive strength -Lower the Transverse /Shear / bonding Strength
Higher the Compressive strength –Higher the Transverse / Shear / bonding Strength.
Traditional Method of Gypsum
•In this process Gypsum is heated to 60-80°C only,
looses only 1/3rdof its water, this low burning process
named as incomplete calcinaion and POP is obtained.
•POP containaits higher level of impurites such as
MgO, Al2O3, Fe2O3, SiO2, CaCO3, MgCO3...
•POP is therefore higher on dry bulk density .
•Lower setting time .
•Lower compressive strength
Hopper-fed furnace-heated batch kiln
Cracks in Plaster due to inferior
Quality of Gypsum
Ashtech Production Precess
A. Gypsum is stored by purity and color. It is then sent
to stock plies for processing
B. Crushing and screened
C. Several different processes of Controlled Heating or
calcinations to 180-190°C
D. Grinding ,mixing , quality check and packing
Controlling the Compressive Strength Profile of Gypsum Plaster :Higher Compressive strength /bending strength of the Gypsum Plaster can be
achieved by Gypsum-Polymer composites.
The table below shows the change in the compressive/Bending strength of
Plaster by adding percentage of Vinyl Based polymers by weight of Dry Plaster
Controlling the Setting Profile of Gypsum Plaster
•When applying gypsum plaster on the wall by hand a series of working steps are required to obtain the desired
•That makes it very Labor intensive. The five to six application steps are done within a time span of about 2 – 3
hours for final smooth finishing.
•The setting process of gypsum during this process is a very important quality characteristic. It must be well
balanced and has to compensate as well for gypsum raw material variations.
•The setting of the Gypsum product can be controlled by manufacturers particular formulation. The desired setting
profile of gypsum plaster can be adjusted using an optimized composition of several different retarders and
additional dosage of accelerators.
•There is rising demand of internal plastering with Gypsum on one hand, whereas there is acute shortage of
applicators on other hand.
•This situation requires to be reviewed seriously.
•Applying gypsum Plaster on the wall by spray machine is the alternate remedy
Plastering machine V/S Manual Work
Automatic Spray Machine
450 m2 /8 hours
Less than 30m2 /8 hours
Mirror finishing in horizontal and vertical level
Rely on Experience of workers
Formulation of Gypsum spray plaster (GSP)
•The use of different retarders and accelerators is state-of-the-art in the gypsum industry for the production
of gypsum spray plaster and of other gypsum based products. The use of these additives allows influencing
the start and finishing of the gypsum setting reaction and the slope of the setting curve. The setting process
can be very well adjusted to the specific application needs. This adjustment is also required to homogenize
the effect of gypsum raw material variations which have a strong impact on the setting process
•ASHTECH formulated a gypsum spray plaster using a basic GSP compound and a number of additives.
The gypsum consisted mainly of natural gypsum blended with Starch ether, cellulose ether, airentraining
agent and retarder/accelerator system were added.
ASHTECH ASSURES YOU THE BEST
QUALITY & SERVICES AT A VERY