Plastering: Essential Information
To achieve a smooth, well-plastered surface needs care and patience. Sometimes, the remedy for a badly cracked wall or ceiling area is to hack off the old plaster and start again. Alternatively, the surface may only need simple patching. Textured finishes can present an attractive ‘face’ and make a pleasant ceiling surface.
Repairing larger cracks is slightly more involved than repairing minor cracks. To repair larger cracks in walls or ceilings, you need a proprietary, medium-grade glasspaper, a glasspaper block, a filling knife or scraper, an old paint brush and a spot board or hawk.
Use the scraper or filling knife to scrape out the old plaster then brush out the dust. Open out the crack, making an under or V-cut, which will help to key the new plaster in place. Brush out any further dust.
The replacementcan be a proprietary type; use a cellulose-based filler for large cracks that have to withstand stress or heat. Mix the filler on the plasterer’s hawk with a little water to a workable consistency. If the mix is too wet, it will not stay in place. Mix enough for only an hour’s work.
Use the brush to dampen the area around the crack and, with a pliable filling knife, press the plaster into the crack, leaving it slightly proud of the sound surface. This can be rubbed down when dry.
On deep cracks, apply the filler in layers, allowing each layer to harden before the next is applied. Level off the final layer with a broad filling knife.
On an emulsioned ceiling, mix a little of the colour with the filler. This will help to make the crack disappear when the area is repainted.
A filled surface crack can also be. Painted with a dilute coat of the emulsion before the area is repainted.
Where damage is extensive, the filler should be mixed with equal parts of clean sand. Fill in a layer at a time, allowing each layer to harden and dry out before the next is applied. Only the surface layer should consist of proprietary filler.
Small, shrinkage cracks often appear in the angle between the walls and ceiling of new buildings. This type of shrinkage is not normally serious but is unsightly.
Use a scraper to open up the crack to 2mm wide. Dampen the plaster along the crack with clean water. Mix the filler to a creamy consistency and use the finger to press the mix into the gap. Allow this to set slightly and then, using a damp brush, clean off the excess. Do not paint for at least 24 hours.
Where the ceiling is plastic surfaced, use a filler formulated for use with this for repair. Use a sharp cutting knife to cut back all the loose surface paper. If the plaster core of the plasterboard is exposed, dampen this and then apply a thin layer of a cold-water mix formulated for use on plastic surfaces.
Special scrim paper tape should be soaked, and then laid, using a paint scraper, in strips over the damaged area. Allow to dry for at least 12 hours. Next, apply a second coat of filler evenly.
Use an applicator, which may be a proprietary type or simply made from a piece of laminate 200mm x 115mm in size secured between two pieces of40mm x 13mm and 200mm long.
Damp round the repair area and apply, with a brush, an even coat of filler. To match the textured surface of the surrounding area, use a texturing tool.
This is a block of, about 150mm x 100mm with a handle. A sponge is fitted to the block and covered with polythene sheet secured round the handle with an elastic band. The pad, which is textured, is then applied to the ceiling to match in the new surface with the old. Excess can be removed with a damp brush.
How to Use Lining Paper
It is possible to disguise hair line cracks particularly on ceilings. The simplest and cheapest way is to cover the area with a lining paper and then paint the surface. If the surface is particularly uneven, embossed, chipwood or pebble-dash paper might be used, their textures camouflaging any irregularities.
More permanent finishes are the plastic type of textured finish. These are applied with special tools but are quite within the scope of the home handyman.
Polystyrene, either inor tile form, also makes an attractive cladding material. It also has the added bonus of raising the surface temperature and helping in the battle against condensation.
10. November 2011 by admin
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