NGfL CYMRU GCaD FLOOR SCREEDING, PLASTERING AND RENDERING.

NGfL CYMRU GCaD

www.ngfl-cymru.org.uk

FLOOR SCREEDING, PLASTERING AND RENDERING

FLOOR SCREEDING, PLASTERING AND

RENDERING

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A mixture of water, sand and cement forms floor screed – also known as ‘semi-dry.’ The minimum thickness required is 50mm. Once screeding is complete, walls can be rendered and plastered.


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Render is used to cover building walls. It can be used externally to repel driving rain, or to provide a decorative surface.

Pigment (colour) may be added to render, so that painting is not needed once the render has set.

Render can also be used internally.

Render is formed by mixing water, sand and cement. Other types of render, including lime render also exist. In ancient times, horsehair was mixed with lime render to add strength. It is still used today in specialist building conservation work, such as in restoring old churches.


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www.ngfl-cymru.org.ukRender, ready to be applied to a wall.


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Water is sprayed onto the wall to prevent moisture from being absorbed too quickly.


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Render is applied evenly to the surface.


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It is then ‘combed’ to provide a ‘key’ for the plaster coat.


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Plastering is an ancient craft which dates back at least 4,000 years.

Examples of gypsum plaster work can be found in the pyramids of Egypt.

Plastering requires few tools, but needs skilled labour to carry out the work.


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Plaster can be applied to either stud and plasterboard walls, or masonry walls. Stud walls are built from timber, to which plasterboard is fixed using plasterboard nails.


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www.ngfl-cymru.org.ukPlasterboard is measured with a steel rule.


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It is then marked and cut using a straight edge and craft knife.


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Correctly sized plasterboard sheets can then be fitted to timbers to form a stud wall.


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Stud wall built, awaiting plastering. Insulation is sometimes placed in the wall cavity to either reduce sound transmission, or to help retain heat.


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Once water is mixed with plaster, the plaster will set. Raw materials should be stored in dry areas, where there is no risk of damage by water.


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Tools should be cleaned after use, and stored correctly. If looked after properly, tools will last many years.


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Plaster is mixed with water to form a smooth paste.

All dry plaster is scraped off the side of the bucket, and put back into the mix.


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Plaster is mixed using a propeller mixer with the blades at an angle of 75º from the surface of the mix.

The water should be clean with no contaminants, and the plaster should be mixed until a smooth, lump-free consistency is reached.


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Where right angles are formed, angle beads are fixed to plasterboard with nails. Angle beads should be made from either plastic or stainless steel to prevent corrosion.


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When masonry walls are built, angle beads are fixed using plaster ‘dabs.’


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Before plastering begins, a mixture of PVA glue and water is brushed on to existing plaster. This stops it drawing moisture from new plaster, which would cause cracks if the new plaster dried out too quickly.


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Plaster is spread evenly using a plastering trowel. Fresh plaster is contained in a bucket, and is held on a plasterer’s ‘hawk.’ These are shown on the next slide.


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www.ngfl-cymru.org.ukPlasterer’s hawk and trowel.


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Plasterers sometimes have to work around obstructions, such as power sockets.


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Other items, such as ceiling roses for light switches also need to be worked around.


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Plasterboard will sometimes need repairing. A water and PVA glue mix is used to damp down the existing surface.


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Holes are the filled with plaster until a smooth finish is formed.


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Walls can be built from metal stud as an alternative to timber. Plywood may be fixed behind plasterboard to provide fixing points for fittings. Metalwork can be fixed to either concrete floor slabs and soffits (ceilings,) or directly to block walls as shown on the next slide.


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Large open areas can quickly be made into several individual areas using metal stud partitioning.


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‘Tape and jointing’ provides an alternative to wet plaster.

Plasterboard sheets are fixed to metal studs, and a tape forms a joint where the two sheets meet. The tape is held in place with a compound which is smoothed once dry.


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A second coat of compound is then applied. Once dry, the surface is painted.


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Large areas can be covered quickly using the tape and jointing method.


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Mouldings are sometimes used between walls and ceilings. A mitre is placed on the moulding to form a 45º angle, and the mould is cut to the required length.


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Once fixed, the moulding providing a finish between walls and ceilings.


NGfL CYMRU GCaD FLOOR SCREEDING, PLASTERING AND RENDERING.

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