Plastering Masonry

Filed Under: Do it yourself, Hardware, Remodeling    by: ITC

To plaster a newly built wall you will not have to do any preparation work to it at all before you fix wooden grounds or metal lath in place.

Then the masonry should be dampened by splashing on clean water with a paintbrush. This will help slow down the rate at which the wall absorbs moisture from the plaster, preventing it from drying out too quickly and possibly cracking.

It is a good idea to practice scooping plaster from the hawk and applying it to the wall before you attempt the job for real. Set the loaded trowel against the wall so that the bottom corner of the blade rests on the ground or bead and the blade is at an angle of about 30° to the wall surface. Move the blade upwards to spread a vertical strip of plaster next to the thickness guide, keeping the blade resting on the guide and gradually reducing its angle as the plaster spreads.

Apply more strips of plaster in the same way, working upwards from the bottom and across the bay adding a good thickness of plaster to the wall.

When the bay is finished, use the long wooden rule to strike it off level with the thickness guides. Place it across the guides and draw it upwards, moving it from side to side in a sawing motion as you go. This will level off the high spots and accentuate the dips. Add more plaster and repeat the process until level.

Before it sets, key the surface for the finishing coat by passing a wooden float, with nails knocked through its face, over the plaster to leave score lines.

When the floating coat has hardened (it should take about two hours), you can apply the finishing coat. This is done in exactly the same way as plastering wallboard, applying two thin coats of Finish plaster to produce a polished, flat and hard surface.

Directions:

1. Scooping plaster from the hawk; put the trowel into the plaster and scoop forwards and upwards.

2. Practising applying paster to the wall; work upwards from waist-height, starting with the trowel at 30 degrees to the wall.

3. As you apply the plaster, tilt the trowel more parallel to the wall surface; keep the hawk close to the wall to catch droppings.

4. Applying the plaster in vertical strips; at the end of each stroke, press the lower edge of the trowel to firm the plaster onto the wall.

5. Ruling off the completed bay; use a straight-edge with a sawing motion to lower any high spots and to show up areas with too little plaster.

6. Scoring the surface to provide a key for the finishing coat; the nails should protrude in through the float.

7. Filling the gap left after taking off the ground batten; level off with the trowel, flush with the hardened plaster on each side.

8. Applying the finishing coat; work from bottom to top and cover the floating coat with a thin layer; apply a second coat. 9 Polishing the finishing coat; wet the surface sufficiently to remove ridges and marks and polish firmly with a perfectly clean, flat trowel.

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