On 17/04/2021 14:35, NY wrote:
Our house is brick built, with mortar rendering over this. The mortar
has been painted with white paint - I can't tell whether it's plain
paint or whether it has sand in it to give it a texture. That was done
by the previous owners before we bought the house two years ago.

Large areas (patches of several square feet) of the paint has suddenly
started flaking off the mortar - it seemed to begin at the same time
(late last year / early this year) in various parts of the wall. The
flakes are several inches square and quite thick as if many coats of
paint had been applied. It is the lower parts of the wall (up to about 6
feet from the ground) which have flaked, although on the higher parts of
the wall, the paint looks to be cracking and bubbling.

The mortar underneath is sound - that has not started to crack off the
bricks.

What is the best way to repaint it? Is it just a case of using a wire
brush to get off any loose paint, and then painting with Sandtex or some
other outside emulsion paint? Or do I need to first paint the mortar
with some sort of primer and then paint that with the white paint?
We had the same problem on some roughcast render. Wire brush and/or
pressure washer, followed by fungicide (which is the bit I suspect the
previous owners neglected) before painting.