Explain POP or Plaster of Paris board

POP [PLASTER OF PARIS] SHEET

            Plaster of Paris is a white powder obtained by heating Gypsum. Gypsum {CaSO4.2H2O} is a calcareous stone available in Gujarat, Rajasthan and many other parts of India and the world. When gypsum is heated to a temperature of 150º C, it gets to a hemi-hydrate state. The reaction is as below

            (CaSO4.2 H2O) + heat  = (CaSO4.½ H2O) + 1.5 H2O

              Gypsum       +   heat  =  Plaster of Paris  +  steam

            To the Plaster of Paris thus obtained, if water is added to form a paste, it becomes hard. In fact, it again goes back gypsum stage. The time taken by this paste to harden depends upon the quality of POP powder and the impurities therein. It can be anything from 2 minutes to half an hour. Manually made POP boards are made with the POP which hardens in about 10 minutes and those made on the machine harden in about 3 minutes.

            Manually, the plain POP boards are made by casting/moulding the paste on a simple plain glass; say of 8mm thickness. A glass of adequate size is kept on the table and has 4 wooden battens fixed at the edges to serve as arresters. The width of these arresters is about 25mm and the height is equal to the desired thickness of the sheet. This tackle is then half filled with POP paste. Then, adequate quantity of jute or plastic fibres is spread on this half filled mould. Immediately on spreading the fibres, the balance paste is filled. The excess POP is removed by a strike, the strike being a teak wood batten long enough to slide on the arresters. The mold thus made, is then allowed to dry for about 10 minutes. The board is then removed from the tackle and allowed to weather for about 4 days in order let excess water evaporate. The pop boards are reinforced by jute fibres or plastic fibres in order to prevent these from crumbling to small dissociated pieces on accidental impacts. The thickness of these manually made boards is normally 12mm, but 15mm or 18mm boards are also used occasionally.

            Plaster of Paris [POP] boards are prepared on machine, adopt a similar process and due to mechanisation, production rate is much faster. Also on machine, larger size boards unto 1.22m x2.44m are made. The machine-made-boards have thicknesses 12mm, 15mm, 18mm and 25mm.

            The POP boards are used for false ceiling, panelling and partitioning. POP boards are cheaper than most of the other boards. These are fire retardant and termite proof. Textured or half-perforated boards serve as good acoustic surface material. POP boards can be painted, laminated or veneered.