On Fri, 9 Nov 2018 09:56:03 +0000
alan_m wrote:

What I've found useful to get a flat surface for filling over
distances of 12 inches is a taping knife which has a long blade and
can be run over the existing wall and the plaster to ensure one is
flush with the other

https://www.toolstation.com/shop/Han...g+Knife/p25000

I just use a plastering trowel, I think the taping knife would be too
flexible to scrape hard enough (the way I do it anyway).