I have a single cinder block wall (approx 40') I will fill the holes with ready mix concrete. I want to cap the top with something smooth.

http://i819.photobucket.com/albums/zz111/lacogada/blockcap_zps3430750d.jpg

Do I use plain mortar, mortar mixed with sand, etc ?

Any advise appreciated.

They sell flat 2" cap blocks, easier than filling and contouring. If appearance is the issue, use a sand mix, keep it fairly dry and contour with a float.

Thanks for reply.

Went to loews this morning and saw the 2" cap you mentioned.
They were in a different spot then where I purchased the cinder blocks so was not aware of them till this morning,

But this wall will be walked on and sat on occasionally so I do not want the blocks to move.

So I would have to fill holes and set cap blocks in mortar ?
Or
Fill holes and make my own cap with mortar ?

What you think ?

Just use mortar toset the caps likke you are putting more block or bricks... no filling needed... they won't be going anywhere for a long, long time.

Thanks smoothy, but I don't get it.

What's to keep the mortar from falling into the cinder block holes ?

You put the morar on the ends of the block... in an inverted "V"... just like you are building a brick or block wall. Here is a video clip.

http://www.youtube.com/watch?v=SSnBWMwQXgk

You do the same thing with the cap...

You just put the mortar along the edges like you lay block and set them in it.

Ah ha... thanks guys.