Laying flags to front of retaining wall

[andyste1]

I'm looking to pave an area that is bounded by a low retaining wall that drops down to a lawn, and would like the finished paving to be flush with the front face of the wall (or perhaps jutting over by an inch or so).

Do I just need to ensure that the sub base is level with the top of the wall or is a different approach called for? My concern is that even a tiny amount of "settling" of the sub-base is going to cause issues to the flags that will be sitting partially on the wall and partially on the sub-base.

[seanandruby]

Your sub base can't be that high, you need to allow for bedding, so keep sub base down 40ml. I would finish at back of wall and place a coping stone. As you say differential settlement would pose a problem.

[Tony McC]

Make sure the sub-base is properly and thoroughly compacted, then allow for a 10-12mm mortar joint between top of wall and underside of flag, but 30-40mm mortar bed between sub-base and underside of flag.

If there is any minor settlement of the sub-base (1-3mm), the mortar bed should be able to carry the flag without too much of a problem, but if you do get significant settlement (>3mm) then look to re-lay the flags at the wall edge.