Question
I am looking to have a mortared chopped block border with Oklahoma stone installed around my flower bed.  This border will be 1 to 2 blocks high.  Should there be rebar installed in the mortar base under the block?  I'm sure it would provide more strength but is it necessary?  Also how deep should the mortar base be?
Thanks!

Answer
I am not familiar with Oklahoma Stone. However, I will assume that this is simply a local name for a common material that I am familiar. Assuming you are in a zone where it freezes regularly then any wall or border where stone will be affixed in mortar should be built using a 'footing' that extends below the frost depth. The footing should be built of 3000 psi concrete (not mortar). The footing should probably have steel in it if you want to be certain of reduced movement and cracking. Also, depending on the length of the wall/border you may need expansion and or contraction joints. The depth of the base or footing is determined by the load of the wall and the local frost depth. Consult a local builder or engineer for exact specifications or recommendations for your area. But for general needs, if the wall or border is not retaining or load bearing and is less than 2 feet high then 8" deep by 12" wide with 2, #3 steel bars continuously run through the footing should be good. All steel should be 2" min from concrete surfaces.
Honestly though, no one goes through this much effort for a border. Most people dig a shallow trench, fill it with a few shovels full of type M or S mortar and press the stones into the stone. This will crack sooner or later but is good enough for most.
Good Luck on your project.


Sean J Murphy, LA,ISA, LEED AP
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