Another wall solution

[chessspy]

Hmmm, I wouldn't have thought so if you dig them deep enough.
you are looking at pressure against the wall which is a turning force.
I wouldn't think it would be enough to push the wall over, particulaly if you brace it with piers, (on your side)
5-1 just means 5 parts soft sand to 1 part cement ( a medium to strong mix which along with concrete blocks forms an incredibly strong wall)
BTW there is no point in mixing the mortar any stronger, (unless you use engineering bricks or similar) as that will only weaken it.(for tecnical reasons we don't need to explore here)
Bear in mind that you should possibly take the precaution of getting a document signed by your neighbour at the other side of the wall which clearly shows the original boundary.

 

[podgeylad]

ok thanks for that

so im going to build 7ft wall 13" thick, foundations will be about 2 1/2 ft deep 27" wide, concrete slab about 1ft deep

does this sound ok ?

 

[chessspy]

Yes, think about bracing it with piers, (pillars) as well.
If you're getting a bricky to build it get him on site for advice about the foundations as well, first.