Replastering Walls and Ceilings
For replastering walls or ceilings you will need the following tools:
• Spot board and suitable support,
• An old firm box of suitable height will do,
• Metal float,
• Angled trowel,
• Gauging trowel,
• Wooden float,
Two-knot stock or a distemper brush,
• Scratcher; one can be simply made from Nails, with their heads removed, driven into a piece of wood.
Prepare the wall by removing any loose materials and lightly brush down with a wet brush.
When patching, there is the benefit of surrounding plaster which limits the area covered and, at the same time, acts as a guide for plaster thickness when ruling off.
When plastering a whole wall there is no such guide and the first operation is to make one.
Mix up a small quantity of backing coat and apply a 150mm2 ‘dot’ of this about 150mm from a side wall and the same distance from the ceiling. Make the dot about 12mm thick and keep it as even as possible.
Repeat with another dot 1.3m below this, using a rule and spirit level to check that the surfaces are vertical. Repeat once more just above floor level.
Check with a line-help will be needed here-that the three dots are in the same plane and amend them as necessary. Now repeat this whole process at the other end of the wall.
This done, place dots intermediately at about l.3m centres across the wall.
Once you have checked that the surfaces of the dots are in the same plane the next step is to join them up with screeds, first vertically and then horizontally.
Mix up a quantity of backing coat and, with the steel laying on trowel, screed between the dots from the floor right up to the ceiling. This done, rule off, preferably using a straight-edge rule about l.8m long, and again check for verticals.
Repeat this process across and then up the wall so that the wall is divided up into convenient working areas.
The remaining areas of brickwork can now be treated in exactly the way as for applying a floating coat on a patched area.
Go over the whole wall with the devil float, wash down any adjacent surfaces and leave to dry out.
If a sanded floating coat is being used. Allow at least 24 hours, but if a lightweight plaster is used, four to six hours is sufficient.
Before applying the finish plaster, test the surface for suction. This is extremely important if the floating coat has been left for longer than the times given. Brush water on to the surface; if it is sucked straight in there is too much suction which can not only weaken the final coat, but make it difficult to apply.
Dampening the wall well should overcome this problem, but if this fails, brush on a bonding coat of PVA or wood(one part PVA to six parts water by volume). This should be done immediately before laying up the finish plaster.
Mix up the finish and skim on another coat with the laying trowel. Start with a band, about trowel width, immediately below the ceiling, then continue, with a vertical movement, over the whole wall, working from left to right if you are right handed or from the other direction if left handed.
Once the wall is covered, repeat the process with the wooden float. Then with the wooden float, apply a third thin coat horizontally. Make sure that any seams are well consolidated.
Apply the final coat of finish plaster with the steel trowel using long, firm, vertical strokes. Finally, polish the plaster using a sprinkling of water as a lubricant.
The angle trowel (or twitcher) should be used between operations to consolidate the corners.
After polishing, clean up adjacent walls and floor before the plaster sets hard.
Ceilings and walls, in older properties, may consist of lath and plaster. Once a ceiling has deteriorated badly it may be necessary to remove it completely rather than trying to do a patch-up job.
Stripping a ceiling is never a clean job, so before starting clear the room completely. Hang dust sheets over the doors to prevent dust travelling to other rooms, and cover the floor.
Use a club hammer and chisel to remove the old ceiling, taking care to clean the joists thoroughly. Punch down, or remove any projecting. – Modern ceilings usually consist of decorative plasterboard or plasterboard covered with a finish plaster coat. Plasterboard is composed of a gypsum core, sandwiched between paper lining.
It is available in various-sized sheets, but for most purposes l.2m x 2.4m is a convenient size. There are two thicknesses – 10mm which should be used at standard 450mm centres – and 13mm for more widely spaced joists.
10. November 2011 by admin
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