On 30/05/2021 17:48, NY wrote:

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, Some of the mortar "grouting" between the slabs has cracked and
disintegrated,
Wait until it's been dry weather for a few days, then tip a good mortar
mix, dry, onto the slabs, and brush it around until it goes into the
cracks. Then go round bashing the slabs with a big lump of wood to
vibrate them, then brush some more in. Then leave it alone for a couple
of weeks, unless you're in a very dry area, in which case sprinkle a bit
of water gently all over and cover it with polythene.

Bill