"RobH" wrote in message
...
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.

"Just enough water to make it damp and no more" sounds similar to the
consistency I've used. I found that any more runny was very difficult to
direct into the gap without it dribbling over the surface of the slabs and
having to be wiped off afterwards; it also led to patches of golden sand in
the wet mixture, rather than the grains of sand remaining coated in grey
cement.

There seems to be no rhyme or reason to which parts set like stone and which
remain the consistency of damp sand. The very first batch I made was partly
used to fill a couple of holes in the rendering on the brick wall of the
house (and that has set solid), but the rest of the same batch has set hard
in places but there are patches which haven't set -- and that's for the same
batch, all used within about 30 minutes.

I'm getting a success rate of about 1/3 ie 2/3 of what I've done will have
to be gouged out with a screwdriver and washed out so I can redo it .

How long does mortar remain workable after it has been made? I presume if it
was starting to set before I'd finished using it, it would get noticeably
more stiff and lumpy, rather than remaining a smooth paste. I'm sure I'm
getting each batch used within about 30 minutes of adding water to the dry
mix.

Is the porosity of the base that the slabs are laid on relevant? Am I right
in wondering if the "just enough water to make it damp and no more" mortar
is drying out by water leaching into the ground (or evaporating from the
surface on a hot day) before the water has had chance to react with the
cement to make it set around the sand?


The ready-mix is made by Tarmac (ie it's not B&Q's own brand of dubious
quality) and the label says "cement 15% aggregates 85%". That's a ratio of
about 5.5:1 - quite a bit less cement than the figure of between 3:1 and 4:1
that I've seen mentioned everywhere. Surprisingly the mixture ratio is not
advertised in large letters - I had to search the various paragraphs of
small print to find the 15%/85% figure.


A lot of what I see when I google "grouting/filling gaps in patio slabs"
makes it sound very easy, so there's obviously something I'm not doing
right!