Finishing Plasterboard

Filed Under: Do it yourself, Home repair, Remodeling    by: ITC

Finishing an Imperial ceiling with a coat of plaster is carried out in a similar manner to finishing off a drywall partition. However, when working above your head (which often presents difficulties of its own) it is best to apply small amounts of plaster at a time to avoid tiring your arms.

Deal with the joints first, spreading a thin layer of plaster down the center of each one and pressing lengths of 2in wide nylon mesh or paper tape into the wet plaster with your trowel. Lightly trowel over the tape then apply another thin layer of plaster on top.

Divide into handy bays; fill in each bay with a thin layer of plaster, but not over the joints. Hold the trowel blade at 30° to the surface of the ceiling; the back edge about 1/Gin clear of the board to provide an even layer. Reduce the blade angle as the plaster spreads and pinch the back edge in as you complete the stroke to stop the plaster falling off. Work away from you to avoid flicking plaster into your face.

When you have filled in all the bays, go over the entire ceiling with another thin layer of plaster. Rule it off with a long metal straightedge to remove the high patches and show up the low spots, which should be filled with a thin coat of plaster.

How you treat the angle between the ceiling and walls depends on whether you are replastering the walls at the same time or not. If not, simply run the corner of the trowel blade along the angle from the ceiling and wall sides to cut out the angle neatly. If you are replastering the wall as well, lay on the floating coat then tape the joint between the wall and ceiling before applying the finish coats. Finish the corner as normal.

Finally, polish the hardened plaster with a clean, wetted trowel blade.

If you intend papering or painting directly over the drywall, the joints must first be made to “disappear”. For this you will need drywall joint compound, paper jointing tape and joint finish (see below).

First spread a layer of compound down the seam and, with a taping knife, press the tape into it. Apply another layer of compound over the top, feathering the edges by going over them with a damp sponge.

When the compound has dried, apply a finishing layer, feathering its edges in the same way. Treat the nail head depressions with compound and finish in the same manner.

At the angles between wall and ceiling, fill large gaps with compound; then apply compound to both wall and ceiling and press a creased length of tape into it. Apply two more layers of compound to wall and ceiling, feathering the edges of each one.

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