Although it is correct to double coat (2 sets) of skimming Plaster onto the surface, knowing when it is time to lay on the second coat of Plaster onto the first one will depend on a few factors to consider before you can apply this second coat, such as, the size of the wall area to Plaster onto, verses the drying time of the first coat of applied Plaster. The surface background & how it is sealed prior to Plastering it in the first place. The room temperature, and even how you mixed your Plaster to name but a few.
Once you have laid your Plaster completely onto your wall for the first coat, immediately clean off your trowel & commence to take out some of the lines & ridges of this first coat, by starting at the very same place on your wall that you began laying on Plaster in the first place, by following the same ‘Plaster application method’ only this time you are Trowelling out some of the ridges & Trowel lines.
Please remember, at this Trowelling up stage, you are not trying to get the perfect finish to your surface, you are just aiding it by making it flatter ready for the second coat of Plaster.
Trowel out, from the top left hand side corner of the wall, nearest the ceiling, that is, if you hold your Trowel in your right hand, remembering to pay attention to your edges & ceiling lines, squashing in excess Plaster, & filling out any voids as you go along, with Plaster that is overlapping onto the wall edge/ceiling next to it, (if it hasn’t too gone solid) moving over towards the far right side corner, and then move back over to start Trowelling out from the centre to bottom left hand corner & finally finishing towards the bottom right hand side of the wall.
Then once you have completed this, you can then mix some more Plaster to apply this second coat onto your reasonably smooth & flat (Plastered) surface.
Ideally, the first coat of Plaster that you have applied, and then Trowelled out some of the marks and lines, should now be reasonably firm to the touch once you have finished Trowelling out, but you should not allow this first coat to become too solid to the touch otherwise when you apply the second coat of Plaster onto it, it will dry into the first coat too rapidly, therefore not adhering, and it will dry too quickly so that you can’t finish it to the required smooth and flat finish.
In summary
1: Apply the first coat of Plaster onto a well sealed surface.
2: Once completed, clean your Trowel and commence to Trowel out some of the ridges and lines.
3: Once completed, touch the Plastered surface and check it is firm to the touch, but don’t allow it to dry out too soon.
4: Mix up a fresh bucket of Plaster and commence to apply Plaster onto the surface to second coat it and follow the same procedures listed above to Trowel out any ridges and lines.
But once the first coat is applied, and then Trowelled out for the first time, if you should find that the Plaster has dried too rapidly to work it further, you can always apply another coat of (mixed) PVA sealer, mixed into cold water, average 50 percent PVA and 50 percent water, coat this onto the surface, let it become tacky to the touch, then apply your second coat of skimming Plaster onto this.
Dale Ovenstone 2009
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