On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape
and thickness - not rectangular concrete slabs). They seem to have
been laid on bare earth, as far as I can see from looking into the
gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder residue
that remains. I'm using ready-mixed mortar from B&Q, with water added
to form a stiff paste which is thick enough to adhere to a palette
knife so I can direct it into the gap (typically 5-20 mm) and then
tamp it down with my fingers (wearing rubber gloves in case the
cement causes skin irritation).

I forgot to say: the mortar is brand new and the bag was only opened a
few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar from
when the patio was first laid (about 10 years, according to neighbours),
it's been a thin crust, in some places only about 5 mm thick, with a
large void below it down to the level of the base on which the slabs
have been laid. Is this normal? I'd have thought the whole depth of the
crack between slabs would have been filled with mortar.


When I laid my patio , about 20 years ago, I put all the pavers / slabs
on a bed of sharp sand / cement mixed at about 7 or 8:1. I have had to
re point the gaps about 3/4 times since and I use a 3:1 mix of builders
sand and cement with just enough water to make it damp and no more. .

That works of for me.

Laying the slabs on bare soil is not a good idea for a start.