Steve wrote:
I am redesigning the back garden of a house I moved in to a few years
ago and as part of the new design I need to move a good sized patio. To
keep things simple I plan to re-use the existing 60 slabs. The problem
is that these slabs are much heavier than the normal purpose made garden
paving slabs I have used in the past.

I have laid a couple of patios over the past 20 years, using slabs up to
450mm square and maybe 30mm thick and I remember it as being hard work,
particularly when it came to positioning and levelling each slab. It was
fine if the slab could be tapped level, first time, but if it needed
relifting and relaying it was really hard on my back.

The slabs I am now about to use are 600mm square and 50mm thick and
therefore weigh about 3 times what the others did. In the past I laid a
full bed of sand over the whole area, then 5 blobs of mortar under each
slab. I'm thinking that this time I should lay, level and mechanically
compact a full sand bed and just lay the slabs straight on to that.

Does anybody have any experience of laying slabs like these? Any advice
or tips to help me survive this job would be very welcome.

TIA

Steve

Funny you should ask because I laid exactly this type of slab last
weekend and it was blinking hard work. I would suggest you get yourself
a friend into help (there was two of us) because lifting and re-laying
the slabs to get them level on a dry mix is really hard work.

We laid the slabs on a dry mix using a couple of spades a spirit level
and a big rubber mallet.

First use a piece of wood to get the dry mix about level (I'm assuming
you have laid hardcore if you need / want it) and then lay the slab on
it as gently as you can. We found the best way to lower the slab was to
place a foot against one side of the slab to act as a pivot and then
lower the slab. It digs in along the side your foot is on but that's
easy to fix in a minute. Mind your fingers though it's really easy to
trap a finger.

Aim to get the slab a couple of millimetres high on the side opposite
your foot. If that's the case hit it with the mallet until it's level.
This compacts the sand and seats the slab.

Check the slab with a spirit level. If the foot side is a little low
(probably will be) _gently_ lift the edge with the tip of a spade and
use the mallet to compact dry mix under the slab (this is best done with
two people).

One thing to watch out for is getting material trapped between the slabs
(only a problem if you are laying them flush) which forces them apart.
To fix that just run a finger along the edge of the already laid slabs
so that you create a _small_ (5 to 10 mm deep) trench by the slab. The
small amount of spare material falls in that gap and allows the tiles to
be push firmly together.

Final points: Don't try compacting the dry mix - it's a complete dead
loss. You just damage it while you lay the slabs and sets solid anyway
The two slabbed areas I built following the above method hold 5500 litre
water tanks and they've not moved a mm. If I had to do it again I would
probably try blobs of cement.