Plaster - Flow Sheet
Sand, technically known as fine aggregate, used for cement plaster works can be natural river sand or crushed stone sand. The plastering is done on almost all building structures – internal walls, external walls, ceilings, etc. The quality of sand is very important for achieving the desired results, namely, a durable protective cover, a smooth finish and architectural style as may be desired, in all buildings.
The quality norms for a good plaster sand dictate that its particles should be granular, should be clean and particle distribution should fall within grading limits of specified micro-fraction zones.
With depleting natural resources and ban on mining of river sand, which had been the primary source for all our concrete and plaster sands, we have no other choice but crush hard rock to produce both concrete and plaster sands. It is, however, a great task for any kind of crusher to crush hard rock to the size of sand particles that would meet the required product grading. It is more arduous for any crusher to produce plaster sand equivalent that would meet gradation as per the code (refer above table).The Vertical Shaft Impact (VSI) crushing was undisputedly found to be the best of all crushing techniques for producing fine aggregates.
The principle of breaking by impact energy induced in VSI to break the rock in its fault lines, is very conducive to make crushed sand of required gradation and specifications. Presently VSI crusher is deployed all over the world in tertiary or quaternary stage crushing of hard rocks for producing manufactured sands.VSI crushing technologies have been innovated in the last few decades to process very abrasive rocks down to less abrasive rocks. VSI model with ‘Rock-on-Rock’ impact-breaking is used for processing abrasive rocks. In less abrasive quarry zones, ‘Rock-on-Steel/Anvil’ models do find greater preference for its higher yield with lower per-ton energy cost.
Fine aggregate conforming to Grading Zone IV of IS: 383 – 1970 is meant to be suitable for plaster sand. However, IS 1542: 1992 – SAND FOR PLASTER exclusively covers the requirements of natural sands and crushed stone sands used in cement mortars for plastering works. The particle size grading of sand for plaster work as per IS 1542: 1992 is produced below:
| IS Sieve Designation | Percentage Passing |
|---|---|
| 2.36 mm | 100 |
| 1.18 mm | 90 – 100 |
| 600 microns | 80 -100 |
| 300 microns | 20 – 65 |
| 150 microns | 0 – 15 |
Note: For crushed stone sands, the permissible limit on 150 microns is increased to 20%
YES possesses specialist knowledge of aggregates crushing and screening. Its portfolio includes VSI crushing technologies, of both versions, Rock-on-Rock and Rock-on-Steel/Anvil. The present effort is to provide to our customers a well-designed, compact and composite crushing & screening circuit to produce quality plaster sand with Rock-on-Steel/Anvil model VSI and a horizontal screen. The plant is designed to process hard rock with low to medium abrasive index.
The above flow-sheet and plant layout are developed for producing 30 TPH of dry plaster sand from low to medium abrasive materials. The feed to the plant will be 5-40 mm of secondary-crushed product or a combination of 5 - 10 mm and 20 - 40 mm excess produced coarse aggregates. The crushing is accomplished in a proven VSI crusher of 760 mm rotor diameter with a rock-on-anvil crushing chamber, which produces cubicle and well graded finer particle steams. All minus 2.36 mm fraction produced will meet the specified IS standards.
The VSI crusher works in a closed circuit with a high-performance horizontal screen (H. Screen), which aides to convert all feed material to < 2.36 mm. The H. Screen with elliptical vibratory motion with slow material travel is the best suited screening device for high-efficiency separation of 0 - 2.36 mm as final product. A provision can be made in the bottom deck to separate excess micro-fines, 200 microns or 150 microns and below, depending upon the need to limit the percentage of this fraction within specified IS code for plaster sands.
The VSI and H. Screen are mounted on a composite, compact and sturdy steel fabricated skid-frame. The material feeding arrangement will be designed to suit to the existing plant disposition or owner’s preferences. What is shown in the enclosed layout is a typical feeding arrangement consisting of a ground level hopper fed by a front-end-loader. A belt conveyor below the hopper extracts and feeds the material to VSI crusher. A set of scissor conveyors are deployed to collect, transport, and deliver the VSI-crushed material to H. Screen. The product fraction, 0-2.36 mm, from the screen is delivered on to a stockpile conveyor. The oversize material is fed back to VSI crusher through screen discharge chute arrangement for further crushing.
VSI crushing is a proven method to generate manufactured sands (M-Sand) that fall within the gradation loop of IS codes. VSI-generated M-Sands have gained acceptance by the civil engineering fraternity around the globe as the right substitute for natural sands. In fact, the M-Sands produced by VSI crushers are preferred in concrete works and in cement mortar preparations because of its particle diversity, cubicle shape, clean and free from impurities.
It is to be noted that VSI crusher with ‘rock-on-steel/anvil’ crushing chamber is recommended for producing M-Sands from less to medium abrasive rock zones only. The concrete sands (0-4.75 mm) and plaster sands (0-2.36 mm) produced by ‘rock-on-steel/anvil’ VSI crushers are known for well-defined cubical shape, consistent gradation and lesser generation of unwanted micro-fines. In addition, ‘rock-on-steel/anvil’ VSI will produce higher percentage passing in a single pass, thereby contributing to lesser re-crushing loads for a given crushing task.
The expected gradation of Plastering M-Sand derived from the discharge of a ‘rock-on-steel/anvil’ VSI and H. Screen circuit (refer Flow-Sheet) will be as follows:
| IS Sieve Designation | IS 1542: 1992 (Percentage Passing) | Plaster M-Sand (Percentage Passing) |
|---|---|---|
| 2.36 mm | 100 | 100 |
| 1.18 mm | 90 – 100 | 80 – 90 |
| 600 microns | 80 -100 | 70 – 80 |
| 300 microns | 20 – 65 | 30 – 40 |
| 150 microns | 0 – 15 | 10 – 20 |
| 75 microns | – | 5 – 9 |
Note: For crushed stone sands, the permissible limit on 150 microns is increased to 20%
The skid-module can produce 0-5.0 mm concrete sands by blending both fractions, namely, 0 - 2.36 mm and 2.36 - 5.0 mm, from H-Screen. The discharge chute of H-Screen will have provision for a metered-tapping of 2.36-5.0 mm fraction on to the same conveyor that collects finer fraction and stockpiles it.
