Baz wrote:
My Son is decorating our front room for us.

Stripped wall paper.
Filled and sanded.
Washed down with Sugar Soap.
Put on a thinned coat of white vinyl matt.
Put on a coat of vinyl matt finish coat.
This coat has dried leaving cracks and crazing, even worst where he cut in
with a brush.
What caused this? paint not thinned enough??

There's still wallpaper paste on the wall. Very careful work with
a low-quality scouring pad (the sort that doesn't help with the
washing up very much!), to avoid scratching the plaster, with
lots of clean warm water will get it off, but you've got to
get the wall *clean* - if you slide your hand over the wet
surface, and the wall feels slippery (even in patches)
then there's more work to do. You could line it,
and then paint on that.... however, I prefer
paint on plaster!