Some advice please

[Polchraine]

I wanted to get a little advice on the final laying of the flags (600x600 textured concrete) for my patio. It will NOT have any vehicle traffic just feet and tables.


There is a two brick high retaining wall for the foundations - the slabs will just overhang.

So far the ground had a skim taken off and what remained is fairly solid and had not been touched for 20,30,40,50 years. About 100 to 120mm of MOT type1 was applied and compacted and then a semi-dry mix was added at around 75mm deep. This has now gone off and is fairly solid.

I am planning to lay the flags on a mortar mix probably using sharp sand. Different advice has suggested sharp or building or mix. I have also had advice on the mix; 10:1, 6:1, 4:1 and 3:1 as well as thickness. Some as thick as 60 or 70mm and some as low as 10mm.

Which sand would you advise and which sand:cement ratio?

What thickness too? It will be a full bed (or as near as possible) with a slope towards the garden (away from the house).

Also, is it necessary to leave a small gap against the house - there is a DPC against the house wall and the finished level is 150mm below DPC.


Thanks in advance

[Pablo]

Sharp sand with a 6:1 ratio just wet enough to make it sticky lay right up to the house no need for a gap. Mortar bed should be approx 40mm. Good luck my only other advice would be to use tight string lines to make it easy to lay each course.

[Polchraine]

Thanks Pablo, the person doing the laying is a very good brickie! - some but not much experience with slabs though. We have plenty of his lines to use along with a 4m straight edge and he is pretty particular about getting straight edges!

[lutonlagerlout]

i prefer a line to a straight edge any day
as most slabs/flags are riven a straight edge is worthless
the mix i use (have laid 70m2 of sandstone this week with it)
is 10 flooring sand 2 soft sand 1/2 bag of cement and 200 ml of SBR
water to suit the mix but when its going round it would look similar to block laying mortar (i lay with wetter than most paviors but i am a brickie too)
after 3 days of laying not 1 rocker with that mix
LLL