Machine Plastering (Application)

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Applying plaster by machine requires preplanning so the operation will go smoothly. The plaster pump should be placed adjacent to the mixer and have sufficient hose attached to the pump to allow quick and easy pumping of plaster from the mixer to the surfaces to be plastered. Hose lengths should be relatively straight and no longer than necessary. Normally, rigid pipe is used to accommodate the high pressures near the pump. Rigid pipe also offers less friction than a rubber hose. Reducing friction and subsequent pressure in the line helps reduce sand packing. Note that aluminum pipe or fittings should not be used to convey plaster. The pipe is coupled to a flexible rubber hose attached to the discharge nozzle. To ease the work effort demanded of the nozzle man, a light flexible whip line hose is used between the flexible rubber hose and the nozzle. The nozzle unit at the end of the pump contains valves that give the operator remote control of the pressurized-air and pump.

Before pumping plaster, the hose should be pre-wetted and lubricated to ensure unimpeded flow of plaster through the hose. Enough water is added to the pump holding tank to partially fill it. The pump is started and begins to move this water through the hose. The pump is stopped, the hose is disconnected at the pump, and a wet sponge is inserted in the hose. Safety considerations dictate that the whip line and nozzle not be connected to the hose at this time. The hose is reattached and the pump is started again. Water under pressure forces the web sponge through the hole. A neat cements slurry ( cement and water without sand) then is poured into the nearly drained pump holding tank. As pumping continues, the neat cement paste is forced through the hose, lubricating all the hose surfaces. When the sponge emerges from the hose at the discharge end, the nozzle man stops the pump, attaches the whip line and nozzle and sprays the remaining water and neat cement paste into a waste container. Since the neat cement paste is intended as lubrication for the hose, the operations involving line changes and nozzle additions should be completed as quickly as possible so the paste does not dry out or harden. The plaster mix is placed in the pump holding tank, pumped through the hose and detected at the nozzle by the presence of sand. When the mixture is uniform in appearance, it is applied to the surface to be plastered.

Good pumping practices require preconditioning, proper maintenance before and during pumping, and good cleanup and preventive maintenance of the hose upon completion of the work. Hose stoppages may occur during work due to poor mixtures or leakage at quick couplers located between pump and pipe, pipe and hose, hose and nozzle. A stoppage requires immediate removal of the obstruction and, if necessary, repair or replacement of equipment. Excessive line pressure will activate the pumps safety valve or possibly rupture a hose. Regular preventive maintenance of the pump should be an established procedure. When pumping is completed, the pump and hoses should be immediately cleaned. Water used to cleanse the mixer is discharged into the pump hopper, and the nozzle is removed from the hose. Water is then added to the hopper while it is cleansed. The fresh water is then pumped through the hose until the hopper is emptied. A sponge is inserted at the pump end of the hose, clean water is added to the pump hopper, and both sponge and water are pumped through the hose to complete the cleaning operation

During pumping applications, the nozzle man holds the nozzle approximately 12 in. from the surface. Plaster is applied to the desired, or slightly greater thickness. The nozzle man can vary the spray pattern and pattern size by adjusting the air pressure, changing the nozzle orifice size, varying the distance between the end of the air stem and orifice, increasing or decreasing pump speed, or calling for a change in water content to adjust the consistency of the plaster mix. Through proper selection of these options, the nozzle man can control the plaster application.

Machine application eliminates lap and joint marks, produces a more uniform appearance in color and texture, and produces, in color finish coats, deeper, darker, and more uniform colors then can be obtained by hand application.

For scratch and brown coats, the nozzle should be moved with a steady even stroke, laying on the proper thickness with one pass and overlapping successive strokes. The angle of the nozzle to the surface should be uniform. Around door bucks and window frames the nozzle should moved close, to within a few inches of the surface.

The same rodding, floating and finishing procedures used after hand application are used after machine application. Manufacturers of plastering machines publish instructions regarding their use, care and maintenance. These instructions should be carefully followed.

There are quite a few plasters but two main types:

• gypsum based and
• cement based.

The latter are used mainly for outdoors, generally for rendering

Cement based plasters can be used indoors for areas that are susceptible to damp and areas that require a greater thickness of cover.

Gypsum based plasters are used indoors only - damp will attack a gypsum based plaster and cause it to crumble.

The most common gypsum plasters are browning, bonding, and metal lathing plaster. Modern plasters come already mixed with perlite, vermiculite and several other additives. These additives provide a greater degree of insulation and fire resistance. Other ingredients slow down the setting time and generally make the mixture more workable.

Today the only additive we need to add is good clean water. When plastering materials with differing absorption, it is a good idea to key the surfaces to be plastered with a PVA bonding sealer. This prevents the plaster 'going off' (setting) at different speeds.

Surface Guide

• Browning plaster (perlite) - Brickwork, Coke breeze, Clay tile partitions, Thermalite blocks, Concrete bricks.
• Bonding plaster (vermiculite) - Concrete, Stonework, Cork slabs, Surfaces treated with PVA.
• Metal lathing plaster (perlite with vermiculite & rust inhibitor) - Expanded metal lathing, wood wool slabs.
• One Coat Plaster - Used for any surface as undercoat and finish.

Skimming plasterboard

Skimming is a term used for applying a thin coat of plaster to a wall or ceiling to provide a smooth uniform surface. The plaster used is generally called 'board finish' and comes in a variety of pack sizes. The amount needed can be worked out by area/weight. 10kg should be sufficient to cover about 5 sq m at a thickness of 3mm. Only buy plaster when you need it, as the shelf life is minimal, and ensure it is kept in a dry room.

Before starting, you should clear out the room and dust down the plasterboard. The idea is to get rid of as much dust as possible since, oddly enough, surfaces need to be kept as clean as possible. Dirt and dust can cause untold problems later and the short time spent cleaning up will pay dividends. A useful tip is, when sweeping up sprinkle a little water on the area to be swept, this keeps the dust to a minimum.

	Plaster Mixing and Conveying Pumps         PFT G5 Mixing Pump The PFT G5 is the most popular mixing pump from the PFT range. It will mix and pump most factory blended dry pre-mixed mortars with water to a homageneous ready to use wet mortar. Being only 65cm wide and having a modular design makes the G5 very transportable and easy to manouver around the building site.   Full specification here...                   PFT MONOJET Mixing Pump The Monojet mixing pump mixes and pumps most factory blended dry and wet pre-mixed mortars and plasters.   Full specification here...                   PFT MULTIMIX Batch Mixer The Multimix batch mixer mixes special mixtures which can be emptied via the rack and pinion gate.   Full specification here...                   PFT Swing II Mobile Conveying Pump The Swing II mobile conveying pump continuously pumps liquid plasters up to a grain size of 3mm along with dispersion paints, primers, etc.   Full specification here...                   PFT Generator The PFT Generator is a petrol powered electrical generator capable of powering any of the PFT plaster and screed equipment.   Full specification here...
Traditionally plastering has been a labour intensive task. The raw materials are measured and mixed in small quantities on site and then the mix is picked up by the tradesman and laid onto the wall prior to floating and trowelling. It is a process often fraught with the possibility of waste and error. The mixture to be applied, whether it be plaster, render, mortar, grout or floor screed, is very sensitive to variations in water content. The skill of the plasterer is not just in the finishing but in the gauging the wetness of the mixture to be applied.  Technology has helped improve the quality and consistency of mixtures through the use of pre - mixed bagged materials ensuring the dry element of the equation is correct. However, the mixtures still require careful wetting. Water ratio, water quality and mixing times all vary according to the product and require skill and time on site to ensure good work. Contractors have now taken a different approach, one which started about 1972, when a machine which accurately wetted and mixed the material was first designed. The aim was not to reduce labour but to make labour more productive enabling skilled workers to have a controllable supply of accurately mixed material ready to be applied. Since then machines have been developed according to job required and the mixtures used, The most popular machine (G5) provides a good example of how the system works. It is a mixing pump which uses a rotor / stator pumping system and which can be used for mortar, projection plaster, textured render, floor screed, concrete repair and with traditional sand and cement mixes. Dry pre - mixed material is fed into the hopper and is transported into the mixing chamber. A constant supply of water, adjustable according to the mixture required, is fed into the chamber to produce a continuous consistent mix. The mixing shaft transforms the dry powder into smooth wet plaster, render, mortar, grout or floor screed in seconds, also drives a rotor / stator pump which conveys the always fresh mixture to the work area. There is a very wide range of machines available which enable contractors to work with all pre - mixed and bagged dry material in a variety of site conditions. The most popular machines are combined mixers and pumps, they offer great flexibility as they can be used with a wide variety of materials. PFT G5 PLASTERING MACHINES PFT G5 Super Plastering Machines have been used in Ireland for over eight years and are becoming more popular  as speed and high quality of finished render is easily achieved. This is due to the fact that machine application is least three times faster than traditional methods as the G5 machine eliminates the hardship of applying material by producing material from powder form to consistent wet mix ready for screeding regardless of the height of the building. ADVANTAGES TO THE ARCHITECT The key benefit of mixing and pumping plastering machines to architects is that of consistent quality, helping to ensure that colour and finish are as envisaged at the design stage. Architects and specifiers also have the facility to select modern materials such as fast flowing, fast drying, self levelling floor screeds and other liquid mortars with the benefit of greater performance, physical properties relevant to their location and reduced drying times. ADVANTAGES TO THE CONTRACTOR For the contractor the key benefit is also that of higher consistent quality, resulting in lesser correction, no hacking off and so reducing the likelihood of rectification costs. Costs are further reduced as construction can proceed more quickly and importantly there is less risk of damage to materials on site. Other advantages to the contractor include early removal of scaffolding, less waste on site and low maintenance cost. But the key benefit is that using a machine enables an accurate account of the material used. For further information on pumping and mixing machines please check out the PFT webpage on: www.pftcentral.co.uk