I will use Garden lime to make up a 1:1:6 mortar for a not too high garden wall. Any comment??

Hi. A 1:1:5 mix Would probably be better as it is a stronger mix. Good luck.

Apart from using lime as a plasticiser to make the mortar workable, lime does nothing else but make the "cement/sand mortar a weaker mix As said 4 sand 1 cement plus feb is fine for a concrete block wall. You can place ½ lime in the mix ratio to make it more workable but it's unnecessary and makes the mortar weaker. Garden lime is not the same as the lime you purchase from a builders merchants

4 sand / 1 cement with some feb.

Hi. It depends what material you are using for your wall. If its a newer brick then use 5 sand and 1 cement, if its a reclaim or hand made brick you could use 5 sand, 1 cement and 1 lime and if its stone use 3 sharp sand, 3 sand, 1 cement and 1 lime (you should expose aggregate in the stone wall hence using some sharp sand). You should also put some plasticiser (febmix) in any mix that doesnt contain lime to aid the playability of the mix. Hope this helps, Rick