I currently have a 4 and a half feet concrete block retaining wall that was unfinished when we moved in to our home. I would like to know if adding another three levels of concrete blocks is a DIY project or it this would need to to be done by professionals.

What's your skill level? Mason here asking. Can walk you through if your skill level is GOOD.

Signed 21 Boat

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I have no skill level. I have never tried building anything before.

Hear one way of looking at it. Since the wall is unfinished it doesn't really matter how smeary the wall gets you could try it.

If that's going south then stop and call a mason and at least the block is there.

What is the finial thoughts on the finish of the wall?/

Retaining walls over a certain height generally require an engineer and a permit. I think you old wall is already over this height.