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AboutSince 2002
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Gypsum plaster,
explained.

58 questions that contractors, engineers and home owners ask about gypsum powder, bonding agent and gypsum board, with short answers. Each figure of ours is measured.

Updated 6 October 2026 · Sai India Gypsum, Panvel

27 sq ft
SIG-MR
from one 25 kg bag at 13 mm, measured on site
20 sq ft
PlastoPlus
from one 20 kg bag at 13 mm: one kilo, one square foot
15 min
setting time
in the test; IS 2547 allows 10 to 30 minutes
1 year
shelf life
in the closed bag, in a dry store

01

The basics

What is gypsum plaster?

Gypsum plaster is a white powder made from the mineral gypsum. You mix it with water and it sets hard on the wall in minutes.

The powder is calcium sulphate hemihydrate (CaSO₄·½H₂O). A factory makes it when it heats gypsum rock and grinds it. On site the powder takes up water again and turns back into gypsum (calcium sulphate dihydrate). This reaction makes the plaster hard.

Gypsum plaster goes on the inside walls and ceilings of a building, in one coat, with a smooth white finish.

Is gypsum powder the same as gypsum plaster?

In the building trade, yes: “gypsum powder” is the usual name for gypsum plaster in a bag.

In strict terms, gypsum powder is ground gypsum rock, and gypsum plaster is that powder after heating, with small additives that control the setting time. The bags of SIG-MR and PlastoPlus carry the words “Gypsum Powder”, because that is the name that contractors use.

What is the difference between gypsum plaster and plaster of Paris (POP)?

Both come from gypsum. Plaster of Paris sets in a few minutes and is used for thin finishing and mouldings. Gypsum plaster has a controlled setting time and is made for a full plaster coat on a wall.

Gypsum plaster for walls must meet IS 2547 (Part 1), which asks for a setting time of 10 to 30 minutes. That time lets a crew mix, apply and level a coat of 6 to 20 mm.

Which Indian Standard applies to gypsum plaster?

IS 2547 (Part 1) is the specification for gypsum building plaster. IS 2542 (Part 1) gives the test methods.

The limits of IS 2547 that our reports are checked against:

PropertyIS 2547 limitWhat it tells you
Setting time10 to 30 minutesThe time that you have to apply and level the mix
Bending (transverse) strengthAt least 0.49 N/mm²The strength of the set plaster
Left on a 150 µm sieveNot more than 5%How fine the powder is
Expansion on settingNot more than 0.2%How little the plaster moves as it sets
Surface hardness (ball indentation)3.0 to 4.5 mm for a final coatHow hard the finished surface is

An NABL laboratory tests SIG-MR against this standard. You can read the reports on the Downloads page.

How does gypsum plaster set, and why does it become warm?

It sets by a chemical reaction with water, not by drying. The reaction gives off heat, so the plaster becomes warm as it sets.

In our tests SIG-MR reaches a peak of 48 to 53 °C while it sets. Because the plaster sets by reaction, it needs no water curing afterwards.

Safety: never let plaster set around a hand, a finger or another part of the body. The heat can cause severe burns.

Does gypsum plaster burn?

No. Gypsum is non-combustible: it does not burn.

This is a property of the mineral gypsum itself. It is not a test result for a wall or a ceiling: that needs a test of the full construction.

02

Gypsum plaster and sand-cement plaster

What is the difference between gypsum plaster and sand-cement plaster?

Gypsum plaster goes on in one coat, sets in minutes, needs no water curing and gives a smooth white surface. Sand-cement plaster needs water curing for several days and usually a finishing coat before paint.

Gypsum plasterSand-cement plaster
Water curingNoneSeveral days
SettingMinutes (IS 2547: 10 to 30)Hours, then days to gain strength
CoatsOne coat, 6 to 20 mmOne or two coats, then often a finishing coat
SurfaceSmooth and white, ready for paint workGrey and rougher
Load on the buildingLessMore
WhereInside walls and ceilingsInside and outside
SupplyReady in the bag: add waterSand, cement and water are mixed on site

Because there is no curing wait, the next trade can start sooner.

03

Coverage and quantity

How much area does one bag of gypsum plaster cover?

At 13 mm thickness, one 25 kg bag of SIG-MR covers 27 sq ft, and one 20 kg bag of PlastoPlus covers 20 sq ft.

Both figures are from walls on site, with the losses included. For PlastoPlus the sum is easy: one kilo covers one square foot at 13 mm.

ProductBagCoverage at 13 mmWall from one kilo
SIG-MR25 kg27 sq ft1.08 sq ft
PlastoPlus20 kg20 sq ft1 sq ft

How does coverage change with the plaster thickness?

Coverage changes in proportion to the thickness. Half the thickness gives twice the area.

Coverage of one bag, worked out from the figure measured at 13 mm:

ThicknessSIG-MR, 25 kg bagPlastoPlus, 20 kg bag
6 mm58.5 sq ft43.3 sq ft
8 mm43.9 sq ft32.5 sq ft
10 mm35.1 sq ft26 sq ft
13 mm27 sq ft20 sq ft
15 mm23.4 sq ft17.3 sq ft
20 mm17.6 sq ft13 sq ft

The sum: coverage at your thickness = coverage at 13 mm × 13 ÷ your thickness in mm.

How many bags of gypsum plaster do I need?

Divide the wall area by the coverage of one bag, and round up to a whole bag. For 1,000 sq ft at 13 mm you need 38 bags of SIG-MR or 50 bags of PlastoPlus.

Wall area at 13 mmSIG-MR, 25 kg bagsPlastoPlus, 20 kg bags
100 sq ft4 bags5 bags
500 sq ft19 bags25 bags
1,000 sq ft38 bags50 bags
2,000 sq ft75 bags100 bags

For another area or thickness, use the calculator on the SIG-MR page or the PlastoPlus page. You can also enter the coverage of another plaster and compare the number of bags.

Why is the coverage on site lower than the figure on a data sheet?

Many data sheets give coverage under laboratory conditions. On a site, an uneven wall and the losses of mixing and application use more plaster.

We measure coverage on a site wall, with the losses included: 27 sq ft from a 25 kg bag of SIG-MR at 13 mm. When you compare two plasters, ask if each figure is from a laboratory or from a wall, and at which thickness.

What changes the coverage of gypsum plaster?

The thickness of the coat changes it most. An uneven wall, wastage and the mix also change it.

  • Thickness. A wall that is out of line needs a thicker coat in places.
  • Wastage. Plaster that sets in the pan before it is applied is lost.
  • The mix. Keep to the water and plaster ratio of the product.

04

How to apply

On which walls can I apply gypsum plaster directly?

On brick and on AAC or concrete block, apply gypsum plaster directly. On smooth concrete (Mivan, RCC, precast), roll on a bonding agent first.

Smooth concrete is dense and gives plaster nothing to hold. Gypbond Pro gives it a rough, bonded key: roll on one coat, wait 24 hours, then plaster. You can plaster up to 14 days after coating; after that, roll a fresh coat. One kilo covers up to 60 sq ft.

The wall must be free of dust and oil.

How do I mix gypsum plaster?

Add the powder to clean water and mix until smooth. For SIG-MR the ratio is 1 part water to 1.25 parts plaster.

  • Use clean water and clean tools. Set plaster left in the pan makes the next mix set faster.
  • Mix only what the crew can apply in one go.
  • Do not add water to a mix that has started to set.

What is the setting time of gypsum plaster?

IS 2547 allows 10 to 30 minutes. SIG-MR and PlastoPlus set in 15 minutes in the test; SIG-MR is also made with up to 30 minutes, to order.

This is the final set of a test sample. The time on site depends on the water, the batch and the weather. Tell us the setting time that you want with your quantity.

When can I paint over gypsum plaster?

Paint when the plaster is dry. The drying time depends on the thickness of the coat, the weather and the air flow in the room.

A whiter plaster base needs less putty and gives paint a brighter colour. SIG-MR has a whiteness of 93% and above.

05

Quality and tests

How do I check the quality of a bag of gypsum plaster?

Scan the QR code on the bag. It opens the test certificate of that batch.

Every bag of SIG-MR and PlastoPlus has this code. The certificate shows the setting time, the whiteness and the other results of the batch. The laboratory reports of SIG-MR are on the Downloads page.

What do the test figures of gypsum plaster mean?

Whiteness tells you how bright the base is. Setting time tells you how long you can work. Bending strength tells you how strong the set plaster is. The sieve test tells you how fine the powder is.

TestSIG-MRPlastoPlusIS 2547
Whiteness93% and aboveAbove 93% in every batchNo limit
Setting time15 minutes (up to 30 to order)15 minutes10 to 30 minutes
Bending strengthOver 8 times the minimumOver 11 times the minimumAt least 0.49 N/mm²
Left on a 150 µm sieveUnder 2%Inside the limitNot more than 5%
Tested byAn NABL laboratoryOur laboratory at the Panvel factory

The full list is on each product page: twelve properties for SIG-MR and fourteen for PlastoPlus.

What is an NABL test report?

NABL is the National Accreditation Board for Testing and Calibration Laboratories of India. An NABL report comes from a laboratory that the board has accredited, and it carries a ULR number.

An NABL laboratory tests SIG-MR against IS 2547. Each report on our Downloads page shows its report number and its ULR number.

06

Storage and safety

What is the shelf life of gypsum plaster?

The shelf life of SIG-MR and PlastoPlus is 1 year in the closed bag, in a dry store.

Keep the bags off the floor and away from damp walls. Gypbond Pro also has a shelf life of 1 year, in the closed bucket.

How do I store gypsum plaster on site?

Store the bags closed, in a dry and covered place, off the floor.

  • Put the bags on a pallet or on planks, not on the bare floor.
  • Keep them away from damp walls and from rain.
  • Use the oldest bags first. The batch and the date are printed on the bag.

If the powder in a bag has hard lumps, it has taken up water. Do not use it.

Is gypsum plaster safe to handle?

Yes, with normal site care. Keep the dust out of your eyes and do not breathe it, and never let plaster set around a part of the body.

Wear a dust mask and eye protection when you open bags and mix. Wash the powder off the skin with water. The safety data sheet of each product is on the Downloads page.

07

Choosing and buying

SIG-MR or PlastoPlus: which one do I choose?

Both are one-coat gypsum plasters from our Panvel factory. SIG-MR covers 27 sq ft from a 25 kg bag. PlastoPlus covers 20 sq ft from a 20 kg bag: one kilo, one square foot.

SIG-MRPlastoPlus
Coverage at 13 mm27 sq ft from a 25 kg bag20 sq ft from a 20 kg bag
Wall from one kilo1.08 sq ft1 sq ft
Setting time15 minutes, or up to 30 to order15 minutes
Packs25 kg, 20 kg and 15 kg bags20 kg bag
TestsNABL laboratory reportsFactory laboratory, each batch

Ask for both in one quotation.

What is the price of gypsum plaster?

We do not print prices on this site. Send your site, the product and the quantity, and we reply with a quotation.

To compare two plasters, compare the cost of the wall, not the cost of the bag: a bag that covers more wall needs fewer bags. The calculators on the product pages do this sum with the prices that you were quoted.

08

Gypbond Pro bonding agent

What is a bonding agent for gypsum plaster?

A bonding agent is a thin coat that goes on smooth concrete before the plaster. It gives the plaster a rough surface to hold.

Mivan, RCC and precast concrete are dense and smooth, and they give plaster nothing to hold. Gypbond Pro is a green, water-based coat with fine grit, made with German polymers and formulation. The grit gives the key and the polymer gives the bond.

Where do I use Gypbond Pro, and where is it not needed?

Use Gypbond Pro on smooth concrete before gypsum plaster: Mivan, RCC and precast. It is not needed on brick or AAC block.

It goes on walls, columns, beams and slab ceilings. Plaster keys to brick and block directly.

Gypbond Pro is not a waterproofing product. Do not use it on a wall with seepage: stop the leak first.

Do I still need hacking when I use Gypbond Pro?

Gypbond Pro is made to take the place of hacking. The coat gives smooth concrete a rough, bonded key without a chisel.

In our site tests the coat held up to 3.3 MPa, and with gypsum plaster over it, the plaster broke before the bond in five of six cores. We have not tested the coat against a hacked wall, so we give no figure for that comparison.

How do I apply Gypbond Pro?

Stir it, and roll on one coat with a roller or a brush. Do not add water.

  • Clean the concrete: no oil, no dust and no release agent.
  • Stir until the grit is even.
  • Apply one coat. The green colour shows which wall is coated.
  • Let it dry for 24 hours, then plaster.

The product is ready to use. Do not dilute it.

How much area does Gypbond Pro cover?

One kilo of Gypbond Pro covers up to 60 sq ft in one coat. A rough or dusty wall can need more.

BucketCovers up to
1 kg60 sq ft
5 kg300 sq ft
10 kg600 sq ft
20 kg1,200 sq ft

For 1,000 sq ft you need about 17 kg: one 20 kg bucket. The calculator on the Gypbond Pro page gives the buckets for your wall.

How strong is the bond of Gypbond Pro?

The pull-off strength of the coat is up to 3.3 MPa, tested on site walls.

An NABL-accredited laboratory glued a disc to the dry coat on site walls and pulled it off (test method ASTM D7234). With gypsum plaster over the coat, the plaster broke before the bond in five of six cores (ASTM C1583).

09

Gypsum board

What is gypsum board?

Gypsum board is a flat sheet with a gypsum core between two papers. It makes false ceilings, partitions and wall linings inside a building.

The boards are screwed to a frame of galvanised steel sections. Only the joints are finished wet, so the work is quick and clean. Pro Max is our imported gypsum board, made on German machinery.

What is the size and the weight of a Pro Max board?

A Pro Max board is 1220 × 1830 mm and 12 mm thick: 4 ft by 6 ft, or 24 sq ft. One board weighs 15.3 kg.

The long edges are tapered and wrapped in paper, for a flat, hidden joint. The face paper is ivory and smooth. The back paper is brown and carries our logo.

How many gypsum boards do I need for a ceiling?

Divide the area in square feet by 24, round up, and add for cuts and waste. A 1,000 sq ft ceiling needs 42 Pro Max boards before waste.

For a partition, count both faces. Sections, screws, tape and joint compound are separate. The calculator on the Pro Max page does the sum.

How strong is a Pro Max board?

A Pro Max board carries more than 660 N along the board and more than 280 N across it before it breaks. IS 2095 (Part 1) asks 500 N and 180 N of a 12.5 mm board.

The figures are minimums from the supplier’s test certificate, for a 12 mm board. They are test loads on the board, not loads that you can hang from it.

Why does the weight of a gypsum board matter?

A lighter board is easier for two people to lift, and it puts less weight on the ceiling frame.

One Pro Max board weighs 15.3 kg. The unbranded boards of the same size that we see in the market weigh 17 to 18 kg. On a 1,000 sq ft ceiling of 42 boards, that is about 640 kg of Pro Max, and about 90 kg more with the heavier boards. Choose the frame from the span table of the section maker.

What frame does a gypsum board ceiling or partition need?

A frame of galvanised steel: ceiling sections for a ceiling, and studs in a floor and a ceiling channel for a partition.

Common practice for a 12 mm board:

PartSpacing
Intermediate channels of a ceiling1220 mm
Ceiling sections457 mm
Partition studs610 mm
Board screws230 mm, and 150 mm at the edges

The span and the load set the final spacing: use the span table of the section maker. A flat ceiling starts with a level frame. We make Metal-Max steel sections at Panvel.

How do I cut and fix a gypsum board?

Score the face paper with a knife along a straightedge, snap the board, and cut the back paper. Fix the board with drywall screws into the steel sections.

  • Lay the boards across the ceiling sections, and stagger the end joints from row to row.
  • Keep screws 10 mm from a paper-bound edge and 13 mm from a cut edge.
  • Set each screw head just under the paper. Do not break the paper.

How do I store gypsum boards?

Store the boards flat, off the floor and under cover. Do not stand them on edge.

Pro Max boards come in pairs. One tape closes each pair at the two short ends. To open a pair, start the tear at one end of the tape: it opens along its middle, and you need no knife.

What is the difference between a gypsum board ceiling and a POP ceiling?

A gypsum board ceiling is made of factory-made boards that are screwed dry to a steel frame. A POP ceiling is made with plaster of Paris on site.

With boards, the thickness and the surface are the same from board to board, and only the joints need wet work. That makes the work quick to fit and to paint.

10

Straight answers

Why should I buy your gypsum plaster?

Because you can check each figure before you buy. Our coverage is measured on a site wall, an NABL laboratory tests SIG-MR, and the QR code on every bag opens the test certificate of that batch.

  • More wall from a bag. 27 sq ft from a 25 kg bag of SIG-MR at 13 mm; 20 sq ft from a 20 kg bag of PlastoPlus.
  • A whiter base. Whiteness of 93% and above.
  • Proof. Laboratory reports on the Downloads page, and a certificate for each batch.
  • Supply. Ex-factory from Panvel to any place, with no minimum order.
  • A coupon in every bag of ₹5 to ₹100, for the Quick Cash app.

I get gypsum powder much cheaper than yours. Why should I pay more?

A cheaper bag is not a cheaper wall. Divide the price of the bag by the square feet that it covers: that is what your wall costs.

The unbranded plasters that we see in the market cover 14 to 15 sq ft from a 20 kg bag. One 25 kg bag of SIG-MR covers 27 sq ft at 13 mm, measured on site.

1,000 sq ft at 13 mmBagsWeight to buy and carry up
SIG-MR, 25 kg bag, 27 sq ft38 bags950 kg
A plaster with 15 sq ft from a 20 kg bag67 bags1,340 kg
A plaster with 14 sq ft from a 20 kg bag72 bags1,440 kg

Put the two prices that you were quoted into the calculator on the SIG-MR page. It shows the cost of the same wall with each plaster. Add the transport and the labour for the extra bags.

Why should I care about whiteness, when I will paint over the plaster?

Because paint does not fully hide a grey base. A whiter base needs less putty and gives paint a brighter colour.

This is what we see on site. SIG-MR and PlastoPlus have a whiteness of 93% and above. The unbranded plasters that we see in the market are at 65 to 85%. On a greyer base, the painter uses more putty to get the same colour.

I am happy with my present supplier. Why should I choose you?

Do not change on our word. Plaster one wall with our plaster, measure it, and compare it with what you use now.

There is no minimum order, so you can buy a few bags for the test. Measure the area that one bag covers at your thickness. Look at the colour of the base beside your present plaster. Scan the QR code and read the certificate of the batch. Then decide.

Every maker says that its product is the best. Are you the same?

We do not ask you to believe that. We give figures that you can check: coverage measured on a site wall, laboratory reports with their numbers, and a test certificate for each batch.

The calculators on our product pages let you enter your own plaster and your own prices. If your plaster is cheaper for the wall, the calculator shows that too.

Is all gypsum powder the same?

No. Two bags can look the same and differ in coverage, whiteness, setting time and fineness.

IS 2547 sets the limits for setting time, strength and fineness, but it sets no figure for coverage or whiteness. Ask each supplier for the coverage at a stated thickness, for the whiteness, and for a test report. See what the test figures mean.

How can I check the coverage of a gypsum plaster myself?

Plaster a measured area with one full bag, and note the thickness.

  • Mark an area on one wall and measure it in square feet.
  • Mix and apply one full bag at an even thickness. Check the thickness at a few points.
  • Measure the area that the bag covered.
  • To compare two plasters, bring both to the same thickness: coverage at 13 mm = area covered × thickness in mm ÷ 13.

Is a 25 kg bag better value than a 20 kg bag?

Not by itself. Compare the wall that each kilo covers, not the weight of the bag.

SIG-MR comes in 25 kg, 20 kg and 15 kg bags, and each kilo covers 1.08 sq ft at 13 mm. PlastoPlus comes in a 20 kg bag, and each kilo covers 1 sq ft.

Is your question not here?

Ask us. We answer, and we add the answer to this page.

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