plaster falling down from window reveals

by a
(louth)

hi can you help how do you plaster window reveals outside....the plaster keeps falling down from the top of the window.....what am i doing wrong

Answer
Put a very thin smear of plaster on first to make sure it sticks. Then you can build up the thickness - but do it in layers (in quick succession) rather than all in one go. Only if it slumps off due to the thickness may you need to let the previous layer dry off a bit.