Tiling on Gypsum

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO. 2H2O. It is widely mined and is used as a fertilizer, and as the main constituent in many forms of plaster, blackboard chalk and wallboard. Gypsum is used for making Plaster of paris, Hard wall plaster, Flooring plaster, Gypsum boards, GFRG(Glass Fibre Reinforced Gypsum) walls, Plaster blocks, Gypsum based self levelling screed, etc.

6 mm coat of gypsum plaster (termed as POP punning) is usually applied on the top of cement plaster to give a smooth finish to it before painting. This is a two stage process and involves various elements like sand, cement and water which has to be mixed onsite. This process is slowly being replaced by a direct application of single coat of gypsum plaster. In gypsum plaster, readymade POP powder is mixed with water and applied directly on the wall.

Gypsum plaster cannot be used for outside walls since they retain dampness. Also gypsum plastering cannot be done in areas which are continuously damp such as bathroom etc.,

• Gypsum plaster is costlier than traditional cement mortar plaster (cement and sand) for same thickness of plaster. But in areas where natural/river sand is not available for construction, cement mortar plastering would require a 6 mm gypsum layer to finish it making cement plaster more costly.

Gypsum surface is a relatively weak material in terms of surface tensile strength in comparison to wood, block work, concrete and metals.

Gypsum plaster is classified as follows:

a) Plaster of paris,
b) Retarded hemihydrate gypsum plaster
               Type I – Under coat:
a) Browning plaster b) Metal lathing plaster
               Type II-Final coat plaster
a) Finish plaster b) Board finish plaster,
c) Anhydrous gypsum plasters are for finishing only, and
d) Keene’s plaster is for finishing only.

Both Indian and Imported gypsum usually comply with IS 2547-1.
1. Loss on Ignition (should be >4 and <9)
2. Insoluble residue
3. SO3 by mass (Min 35% as per IS 2547)
4. CaO by mass (Min 2/3 of SO3)
5. Soluble Mgo (Min 0.3%)
6. Soluble Sodium Salt (Na2o - Max 0.3%)

Gypsum surface is water sensitive and is therefore not good to use in wet areas such as bathrooms, showers, kitchens or wet rooms and at exposed situations.

Gypsum surface can be very dusty or, it can be very dense and shiny.

When cement based / dispersion / reaction adhesive used on gypsum surface, the bonding will be weak.

Tiling can be done on Gypsum surface by adopting the following procedures:

1. Remove the surface dust, weak layer and other contaminants.

2. Check with the manufacturer of Gypsum material for its surface strength, how much it can bear the load, accordingly chose the tiles.

In general, maximum weight of tiling acceptable on a dry, well-adhered gypsum background is of 20 kg/Sqm.

3. Apply sealer coat / waterproofing coat by taking the advice of tile adhesive manufacturer.

4. Install the tiles using specified adhesive.

5. Maintain minimum tile joints of 2mm in walls and 3mm on floor.

4. Grout the tile joints using cement based adhesive in non-wet area and epoxy based grout in wet areas.
Know more details regarding different type of putty and POP: https://gharpedia.com/pop-white-cement-acrylic-wall-putty/ Courtsy of Gharpedia.com