How to repair plaster walls and ceilings
March 15, 2012
Although plaster is known to be rigid and susceptible to cracks and stress, it is still chosen for interior wall and ceiling decoration because it is more visually stunning when finished compared to the drywall material commonly applied in home decoration. Another more important reason is that should a crack form on the plaster decoration, in most cases it is relatively easy to repair without the need for a plastering expert.
The steps involved in repairing a plastered wall and/ or ceiling are:
- Step 1) The old, chipped plaster is removed from the substrate before any repair is to be done. Ensure that debris is removed thoroughly. Note: if the stress lines appear to run in a diagonal direction, then there is no need to chip away the old, ruined plaster but instead immediately repair the plastering surface by application of drywall plastering compound with drywall tape added to seal holes and stress lines ( see Fig. 1 for what a drywall tape looks like). If the stress lines appear to run in a horizontal direction, it shows this is a serious problem because it is thought that the cause of this is due to the lathe (the lathe is a platform made up of horizontal strips of wood stuck together to support the plaster when it is being applied to the substrate (see Fig.2 for a pic of a lathe)).
Fig.1 Drywall tape Fig.2 Lathe
- Step 2) Drywall setting compounds are applied to the area where the stress is found. Drywall setting compounds. The time taken for the compound to dry can range from 20 minutes to 90 minutes. (See Fig. 3 for a pic of a fast drying setting compound). The drywall setting compound is mixed with water until it has a consistency that is not too runny or too thick. The drywall setting compound is applied smoothly and evenly over the cracks/lines.
Fig.3: drywall setting compound
- Step 3) The drywall tape is now applied to the setting compound to cover the cracks or stress lines. A 4″ or 6″ drywall taping knife is used to press the tape into the setting compound. Note: there should be setting compound wetting both sides of the tape. Excess setting compound is removed by wiping it away with the drywall knife. (See Fig. 4 for an example of a drywall tape and Fig.5 for an example of a drywall taping knife.)
Fig.4: drywall tape Fig.5: drywall taping knife
- Step 4) Make sure the tape is embedded in the mud well because this is so important. Once this is done allow time for drying. When the setting compound has dried, sand the edges lightly. Apply a second coat of drywall setting compound using a 8″ or 10″ drywall floating knife. Spread the second coat evenly and if necessary, sand down any uneven surfaces.
- Step 5) In this final step, apply a final coat of drywall setting compound using a 12″ or 14″ drywall taping knife. Note: this last coat should have thinner consistency than the previous coats and should be applied in such a way as to achieve the smoothest texture.
How to Apply Plaster
February 15, 2012
The one thing that all “professional” plasters have in common is that they are difficult to apply. They come in large unwieldy bags and have to be mixed with water; they normally set more quickly than the do-it-yourself enthusiast can cope with; it is easy to drag them off the wall when you are applying them; you need a lot of practice to obtain a smooth, even finish; and generally they can be put on only in thin layers.
Do-it-yourself plasters have been specifically designed to overcome all these problems. Two grades are available, repair and finish, and are usually available ready-mixed in small tubs, although sometimes as a powder for mixing with water.
Repair or one-coat plaster is much easier to apply than conventional undercoat plaster and can be used in thicknesses up to 50mm (2in). It can be employed either for filling deep holes – the kind you might be left with when a waste pipe has been removed from a wall – or to provide a base for the finish plaster, although do-it-yourself repair plasters are often smooth enough on their own as a basis for wall tiles and many wallpapers.
Do-it-yourself finish plaster, also known as plaster skim, can be applied up to 3mm thick. As well as providing a finish over repair plaster, it can also be used for smoothing a rough surface and for covering over plasterboard.
How to apply plaster
All types of plaster can be applied with a plasterer’s trowel. Carry the plaster to the wall on a hawk, a square flat board mounted on a short handle, and lift a small quantity of plaster off the hawk on to the wall using the plasterer’s trowel. Spread it out with a sweeping motion. Always keep the trowel blade at an angle to the wall and allow the plaster to squeeze out through the gap between the bottom blade edge and the wall. When the plaster is starting to dry, it can be smoothed over, holding the trowel at an angle.
To ensure that a plaster repair is flush with the surrounding plaster, use a straight-edged length of wood and smooth over with a side-to-side motion, resting the ends on the nearby dry plaster surface.
Finish plaster is applied in the same way, but is polished with a flat trowel when almost dry. Some finishing plasters are applied with a brush, although a plastic spreader will be needed to give it a final smoothing.
Plasterboard
In a timber-framed house, the inner surfaces of exterior walls will be plasterboard (gypsum board), which is solid plaster contained by paper, as will the surfaces of all internal dividing walls. These may be given a skim coat of plaster to cover up the joints between adjacent sheets of plasterboard, or they can have the joints and nail holes filled before painting or papering. Some interior dividing walls in masonry walled houses may comprise plasterboard mounted on timber frames.