"RobH" wrote in message
...
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.

Not very well tho given that you have had to redo the mortar 3/4 times.

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